Chemistry Part I Chapter 7 Equilibrium
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    NCERT Solution For Class 11 Chemistry Chemistry Part I

    Equilibrium Here is the CBSE Chemistry Chapter 7 for Class 11 students. Summary and detailed explanation of the lesson, including the definitions of difficult words. All of the exercises and questions and answers from the lesson's back end have been completed. NCERT Solutions for Class 11 Chemistry Equilibrium Chapter 7 NCERT Solutions for Class 11 Chemistry Equilibrium Chapter 7 The following is a summary in Hindi and English for the academic year 2021-2022. You can save these solutions to your computer or use the Class 11 Chemistry.

    Question 1
    CBSEENCH11006300

    What is equilibrium?

    Solution
    It may be defined as a state in all changes or reactions carried in a closed vessel, where the measurable properties of the system such as colour, density, vapour pressure, concentration, temperature etc. do not show any further noticeable change.
    Question 2
    CBSEENCH11006301

    Give two examples of physical equilibrium.

    Solution

    (i) Evaporation of water in a closed vessel.

    (ii) Dissolution of a gas in a liquid under pressure in a closed vessel.

    Question 3
    CBSEENCH11006302

    What kind of molecules in a liquid can evaporate?

    Solution
    The molecules having high kinetic energies can evaporate.
    Question 4
    CBSEENCH11006303

    Name the factors on which vapour pressure of any liquid depends.

    Solution
    Factor at which vapours pressure of a liquid depends on:(i) Temperature (ii) Nature of liquid.
    Question 5
    CBSEENCH11006304

    Under what condition solid rightwards harpoon over leftwards harpoon liquid, equilibrium can exist?

    Solution
    At the melting point or freezing point.
    Question 6
    CBSEENCH11006305

    Which property becomes constant in the following equilibria:
    left parenthesis straight i right parenthesis space Solid space rightwards harpoon over leftwards harpoon space space Solution space equilibrium
left parenthesis ii right parenthesis space Gas space rightwards harpoon over leftwards harpoon space space space Solution space equilibrium ?

    Solution

    The following property becomes constant in the equilibria.
    (i) A solubility of the solid
    (ii) Mass of the gas dissolved.

    Question 7
    CBSEENCH11006306

    Which measurable property becomes constant in water vapour equilibrium?

    Solution
    Vapour pressure becomes constant in water-vapour equilibrium.
    Question 8
    CBSEENCH11006307
    Question 10
    CBSEENCH11006309

    How a reversible reaction is expressed?

    Solution
    A reversible reaction is expressed by showing two half arrows in opposite directions in between the reactants and the products
    left parenthesis straight R space rightwards harpoon over leftwards harpoon space straight P right parenthesis.
    Question 11
    CBSEENCH11006310
    Question 12
    CBSEENCH11006311
    Question 13
    CBSEENCH11006312

    What is a forward reaction?

    Solution

    A forward reaction is a reversible reaction in which reactants produce products, and a reverse reaction turns those products into their original reactants.

    Question 14
    CBSEENCH11006313

    What condition favours a reversible reaction?

    Solution
    The reaction should be carried out in a closed vessel.
    Question 15
    CBSEENCH11006314

    What is a backward reaction?

    Solution
    In a reversible reaction, the reaction that proceeds from right hand side to the left hand side is called backward reaction.
    Question 16
    CBSEENCH11006315
    Question 17
    CBSEENCH11006316

    What is meant by a system at dynamic equilibrium?

    Solution

    It is a system, in which the forward and backward reactions proceed at the same rate and the respective quantities remain unaltered.

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    Question 18
    CBSEENCH11006317

    discuss the effect of a catalyst on equilibrium ? 

    Solution
    The presence of catalyst does not change the position of equilibrium. It simply fastens the attainment of equilibrium.
    Question 19
    CBSEENCH11006318

    At equilibrium, the mass of each of the reactants and products remains constant. Does it mean that the reaction has stopped? Explain.

    Solution
    No, the reaction does not stop. It continues to take place in the forward as well as backwards directions but at equal speeds.
    Question 20
    CBSEENCH11006319

    What is the effect of a catalyst on the position of equilibrium?

    Solution
    A catalyst does not affect the position of equilibrium because it increases the rate of the forward and backwards reactions equally.
    Question 21
    CBSEENCH11006320

    Under what condition, a reversible process becomes irreversible ?

    Solution
    When one of the product (gaseous) is allowed to escape out (i.e. in an open vessel).
    Question 22
    CBSEENCH11006321

    Give two important characteristics of the equilibrium constant.

    Solution

    Characteristics of equilibrium constant:
    (i) It changes with temperature.
    (ii) It does not change with concentration.

    Question 23
    CBSEENCH11006322

    Give the equilibrium constant for the following equilibrium in terms of partial pressures:

    straight N subscript 2 left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space 2 NH subscript 3 left parenthesis straight g right parenthesis.

    Solution

    Equilibrium constant in terms of partial pressures:
    straight K subscript straight p space equals space fraction numerator straight p subscript NH subscript 3 end subscript superscript 2 over denominator straight p subscript straight N subscript 2 end subscript space cross times space straight p cubed subscript straight H subscript 2 end subscript end fraction

    Question 24
    CBSEENCH11006323

    What is the relation between Kp and Kc?

    Solution

    Kp = Kc (RT)∆n, where Kp is the equilibrium constant in terms of partial pressure.
    Kc is the equilibrium constant in terms of concentration, R is gas constant, T is kelvin temperature and ∆n = No. of moles of the gaseous products – No. of moles of the gaseous reactants.

    Question 25
    CBSEENCH11006324

    Under what condition in a reversible reaction is Kp = Kc?

    Solution
    Kp = Kc when the moles of gaseous reactants and product are same e.g.
    straight H subscript 2 left parenthesis straight g right parenthesis space plus space straight I subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space 2 HI left parenthesis straight g right parenthesis
    Question 26
    CBSEENCH11006325

    Predict which of the following reaction will have appreciable concentration of reactants and products:
    left parenthesis straight a right parenthesis space Cl subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space 2 Cl left parenthesis straight g right parenthesis comma space space straight K subscript straight C space equals space 5 space cross times space 10 to the power of negative 39 end exponent
left parenthesis straight b right parenthesis space Cl subscript 2 left parenthesis straight g right parenthesis space plus space 2 NO left parenthesis straight g right parenthesis space space space leftwards harpoon over rightwards harpoon space 2 NO subscript 2 Cl left parenthesis straight g right parenthesis comma space space straight K subscript straight c space equals space 3.7 space cross times space 10 to the power of negative 8 end exponent
left parenthesis straight c right parenthesis space Cl subscript 2 left parenthesis straight g right parenthesis space plus space 2 NO subscript 2 left parenthesis straight g right parenthesis space leftwards harpoon over rightwards harpoon space space 2 NO subscript 2 Cl left parenthesis straight g right parenthesis comma space space straight K subscript straight c space equals space 1.8


    Solution
    For reaction (c), as Kc is neither high nor very low, reactions and products will be present in comparable amounts.
    Question 27
    CBSEENCH11006326

    PCl5, PCl3 and Cl2 are at equilibrium at 500K and having concentration 1·59M PCl3, 1·59M Cl2 and 1·41 M PCl5. Calculate Kc for the reaction:
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    Solution
    Applying the law of chemical equilibrium, we have
                                straight K subscript straight c space equals space fraction numerator open square brackets PCl subscript 3 close square brackets space open square brackets Cl subscript 2 close square brackets over denominator open square brackets PCl subscript 5 close square brackets end fraction space space space space space space space space... left parenthesis 1 right parenthesis
    Putting the values in expression (1), we have
                                straight K subscript straight c space equals space fraction numerator 1.59 space cross times space 1.59 over denominator 1.41 end fraction space equals space 1.79
    Question 29
    CBSEENCH11006328

    At equilibrium, the concentration of N2 = 3·0 × 10–3 M, O2 = 4·2 × 10–3 M and NO = 2·8 × 10–3 M in a sealed vessel at 800K. What will be Kc for the reaction:
    straight N subscript 2 left parenthesis straight g right parenthesis space plus space straight O subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space 2 NO left parenthesis straight g right parenthesis

    Solution

    We have given,
    N2 = 3·0 × 10–3 M,
    O2 = 4·2 × 10–3 M
    NO = 2·8 × 10–3 M
    Applying the law of chemical equilibrium. We have
                         straight K subscript straight c space equals space fraction numerator open square brackets NO close square brackets squared over denominator open square brackets straight N subscript 2 close square brackets space open square brackets straight O subscript 2 close square brackets end fraction space space space space space space... left parenthesis 1 right parenthesis
    Putting the values in expression (1), we have
    straight K subscript straight c space equals space fraction numerator left parenthesis 2.8 space cross times space 10 to the power of negative 3 end exponent straight M right parenthesis squared over denominator left parenthesis 3.0 cross times 10 to the power of negative 3 end exponent straight M right parenthesis thin space left parenthesis 4.2 space cross times space 10 to the power of negative 3 end exponent straight M right parenthesis end fraction space equals 0.622

    Question 30
    CBSEENCH11006329

    The following concentrations were obtained for the formation of NH3 from N2and H2 at equilibrium at 500K. [N2] = 1·5 × 10–2 M, [H2] = 3·0 × 10–2M and [NH3] = 1·2 × 10–2 M. Calculate the equilibrium constant.

    Solution
    The reaction is
    space straight N subscript 2 left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space 2 NH subscript 2 left parenthesis straight g right parenthesis
    We have given,
    [N2] = 1·5 × 10–2 M
    [H2] = 3·0 × 10–2M
    [NH3] = 1·2 × 10–2 M
    Applying the law of chemical equilibrium, we have
    straight K subscript straight c space equals space fraction numerator open square brackets NH subscript 3 close square brackets squared over denominator open square brackets straight N subscript 2 close square brackets space open square brackets straight H subscript 2 close square brackets cubed end fraction space space space space... left parenthesis 1 right parenthesis
    Putting the values in expression (1), we have
        straight K subscript straight c space equals fraction numerator left parenthesis 1.2 space cross times space 10 to the power of negative 2 end exponent right parenthesis squared over denominator left parenthesis 1.5 space cross times space 10 to the power of negative 2 end exponent right parenthesis thin space left parenthesis 3.0 space cross times space 10 to the power of negative 2 end exponent right parenthesis cubed end fraction
space space space space equals space 0.106 space cross times space 10 to the power of 4 space equals space 1.06 space cross times space 10 cubed
    Question 31
    CBSEENCH11006330

    Why do we sweat more on a humid day?

    Solution
    On a humid day, there is a large amount of water vapours in the air around us. Therefore, evaporation of water from the skin does not occur quickly. Hence, water vapours do not dry up easily causing sweating.
    Question 33
    CBSEENCH11006332

    What happen when some product is removed from a system at equilibrium?

    Solution
    The rate of the forward reaction increases and the equilibrium shifts towards the products side.
    Question 34
    CBSEENCH11006333

    How does magnitude of equilibrium constant tell about the extent of reaction?

    Solution
    The Greater value of K indicates the greater extent of reaction in the forward direction.
    Question 35
    CBSEENCH11006334

    The value of equilibrium constant is less than zero. What does it indicate?

    Solution
    This indicates that the forward reaction has proceeded only to a small extent before the equilibrium is attained.
    Question 36
    CBSEENCH11006335

    What is the effect of temperature on the equilibrium state of a system at equilibrium?

    Solution

    In exothermic reactions, increase in temperature decreases the equilibrium constant, K, whereas, in endothermic reactions, increase in temperature increases the K value.

    Question 37
    CBSEENCH11006336

    What happens to the equilibrium state of a reversible reaction if the pressure is varied ?

    Solution
    If the pressure is increased, the equilibrium shifts to that side with a lower volume and if the pressure is decreased, the equilibrium shifts to that side with larger volume.
    Question 38
    CBSEENCH11006337

    What is the effect of change of concentration on the rate of reaction?

    Solution
    The rate of the forward reaction increases, if the concentration of the reactants is increased.
    Question 39
    CBSEENCH11006338

    CaO space plus space straight H subscript 2 straight O space space rightwards harpoon over leftwards harpoon space space space Ca left parenthesis OH right parenthesis subscript 2 space plus space kJ
    What is the effect of temperature over the solubility of CaO?

    Solution
    This is an exothermic reaction. If the temperature is increased, the rate of the backwards reaction increases and the solubility of CaO decreases.

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    Question 40
    CBSEENCH11006339

    What is the effect of pressure on the following system?

    PCl subscript 5 space rightwards harpoon over leftwards harpoon space space space PCl subscript 3 space plus space Cl subscript 2

    Solution
    PCl subscript 5 space rightwards harpoon over leftwards harpoon space space PCl subscript 3 space plus space Cl subscript 2
1 space mol space space rightwards harpoon over leftwards harpoon space space 1 space mol space space space 1 space mol
    The increase of pressure favours the backward reaction, where there is a decrease in volume.
    Question 41
    CBSEENCH11006340

    straight N subscript 2 left parenthesis straight g right parenthesis space plus space straight O subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space 2 NO left parenthesis straight g right parenthesis semicolon space increment straight H space equals space plus ve
    What is the effect of temperature over this equilibrium?

    Solution
    This is endothermic reaction. Increase of temperature favours the forward reaction.
    Question 42
    CBSEENCH11006341

    The reaction
    straight N subscript 2 left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space 2 NH subscript 3 left parenthesis straight g right parenthesis is at equilibrium, NH subscript 3 formed is absorbed in sulphuric acid, what happens to the equilibrium?

    Solution
    Since the NH3 is absorbed in sulphuric acid, thus, the equilibrium shifts to the right side.
    Question 43
    CBSEENCH11006342

    What happens when pressure is applied on ice?

    Solution
    Ice begins to melt.
    Question 44
    CBSEENCH11006343

    Define Le-Chatelier's principle ?

    Solution
    Le-Chatelier’s principle state that when a stress is applied to a chemical system at equilibrium, the equilibrium will shift to relieve the stress.
    Question 46
    CBSEENCH11006345

    What is a physical equilibrium? What type of equilibria are involved in physical equilibrium?

    Solution
    Physical equilibrium: When two or more than two phases of a substance exist in equilibrium with each other, it is called physical equilibrium. In such equilibrium, there are only physical changes in the system. For example:
    (i) Solid-liquid equilibrium: Here, solid form of a substance remains in equilibrium with its liquid form.
    straight H subscript 2 straight O left parenthesis straight s right parenthesis space space rightwards harpoon over leftwards harpoon space space straight H subscript 2 straight O left parenthesis l right parenthesis
    A solid and liquid form of a pure substance remain in equilibrium only at a fixed temperature which is called melting point of solid or freezing point of a liquid form of the substance.
    (ii) Liquid-gas equilibrium: Here liquid and gaseous phase of the substance are in equilibrium.
    straight H subscript 2 straight O left parenthesis l right parenthesis space space rightwards harpoon over leftwards harpoon space space straight H subscript 2 straight O left parenthesis straight g right parenthesis
    The equilibrium state is reached when the rate of vaporisation becomes equal to the rate of condensation of vapour to liquid in a closed container. At equilibrium state, even though molecules still move from liquid to vapour and from vapour to liquid state, there is no change in the quantity of the substance in each state because the two processes viz evaporation and condensation take place at the same rate. Thus, physical equilibrium is dynamic in nature.
    (iii) Solid-vapour equilibrium : Solid and gaseous forms of a substance remain in equilibrium.
    straight l subscript 2 left parenthesis straight s right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space straight l subscript 2 left parenthesis straight g right parenthesis
    When solid is changed directly into vapour form, the process is called sublimation.
    Question 47
    CBSEENCH11006346

    What is the effect of pressure on the solubility of a gas in a liquid?
    Or
    State Henry's Law.

    Solution
    The effect of pressure on the solubility of a gas in the liquid was studied by Henry. This law states that the mass of a gas dissolved in a given mass of solvent at any temperature is directly proportional to the pressure of the gas above the solvent, i.e.
                                      straight m proportional to space straight p
    or                                straight m space equals space straight K subscript straight p
    where K is constant of proportionality and called Henry's constant. 
    As the pressure of the system (liquid and gas above the liquid surface in the container) increases, the gas above the liquid surface undergoes a contraction in volume. In other words, the volume of the gas per unit area will decrease. As a result, the gas molecules have a greater tendency to get condensed and get absorbed by the liquid. Hence solubility of gas increases with the increase of pressure.
    Question 48
    CBSEENCH11006347

    Explain why the gas fizzes out (bubbles out) when a soda water bottle is opened?

    Solution
    In soda water bottle, CO2 gas is dissolved in water only under pressure. As soon as the bottle is opened, the pressure inside the bottle tends to decrease the atmospheric pressure, so the solubility decreases. The dissolved gas escapes from the bottle all of a sudden resulting in fizz. 
    Question 49
    CBSEENCH11006348

    A liquid is in equilibrium with its vapour in a sealed container at a fixed temperature. The volume of the container is suddenly increased.
    (i) What is the initial effect of the change on vapour pressure?

    (ii) How do rates of evaporation and condensation change initially?

    (iii) What happens when equilibrium is restored finally and what will be the final vapour pressure?

    Solution

    (i) Vapour pressure will decrease initially.
    (ii) The rate of evaporation remains constant at a temperature in a closed vessel. However, the rate of condensation will be low initially due to the presence of lesser molecules per unit volume in the vapour phase and hence the number of collisions per unit time with the liquid surface decreases.
    (iii) When equilibrium is restored finally, then the rate of evaporation becomes equal to the rate of condensation. The final vapour pressure will be the same as it was initial.

    Question 50
    CBSEENCH11006349

    What are the general characteristics of equilibria involving physical process?

    Solution

    (i) In case of liquid  rightwards harpoon over leftwards harpoongas equilibrium, the vapour pressure of the liquid becomes constant at a given temperature. 
    (ii) In case of solid rightwards harpoon over leftwards harpoon   solution equilibrium, the concentration of solute in solution becomes constant at a given temperature.
    (iii) In the case of gas rightwards harpoon over leftwards harpoonsolution equilibrium, the pressure of the gas above liquid becomes constant at a given temperature. 
    (iv) In the case of solid rightwards harpoon over leftwards harpoon  liquid equilibrium, there is only one temperature (melting point) at which two phases can co-exist i.e. temperature remains constant at a given pressure.

    Hence the common characteristics of physical equilibrium are:
    1. Equilibrium can be established only in case of a closed system.
    2. The equilibrium is dynamic in nature i.e. the process does not stop after the establishment of equilibrium but the rate of the forward reaction becomes equal to the rate of backward reaction.
    3. The measurable properties of the system such as melting point, boiling point, vapour pressure and solubility remain constant since the concentration of the substances remains constant.
    4. When equilibrium is attained there exists an expression involving the concentration of reacting substances which acquire a constant value at a given temperature.
    5. In the case of a gas dissolving in a liquid, the increase of pressure always increases the solubility of the gas in the liquid.

     

    Question 51
    CBSEENCH11006350

    Can equilibrium be achieved between water and its vapour in an open vessel? Explain your answer and say what happens eventually.

    Solution
    We know that equilibrium cannot be achieved in an open vessel. This is because in the case of an open vessel, water vapours will keep on escaping into the atmosphere and reverse process i.e. condensation of vapours back to water cannot take place. Equilibrium can be achieved only if in the system, two opposing processes take place simultaneously. Eventually, slowly and slowly, the whole of the water will change to vapours which escape out of the vessel and the vessel will become dry.
    Question 52
    CBSEENCH11006351

    A vessel has two compartments connected at the top. In one compartment (B), radioactive methyl iodide (CH3I) is placed and in the other (A) normal methyl iodide (CH3I) is placed. Will the vaporus over (A) and (B) become radioactive?
    Will the radioactivity spread to the liquid in the compartment A? Discuss in terms of dynamic nature of the equilibrium between vapours and its liquid.

    Solution
    (i) Yes, the vapours over both the compartments A and B will become radioactive. This is because the vapours formed over A and B can diffuse into each other.

    (ii) Yes, the radioactivity will also spread to the liquid in the compartment A. This is because equilibrium is dynamic in nature i.e. processes of evaporation and condensation continue at equal rates even after the attainment of equilibrium as the space above the compartments A and B contains vapours of both radioactive CH3I and nonradioactive CH3I. Now the vapours of radioactive CH3I will condense in compartment A, thereby making the liquid in compartment A radioactive.
    Question 53
    CBSEENCH11006352

    A liquid is in equilibrium with its vapours in a sealed container at a fixed temperature. The volume of the container is suddenly increased.

    (i) What is the initial effect of the change on the vapour pressure?

    (ii) How do the rates of evaporation and condensation change pressure?

    (iii) What happens when equilibrium is restored finally and what will be the Final vapour pressure?

    Solution

    (i) The initial effect on the vapour pressure of increasing the volume of the container will be that the vapour pressure is lowered. This is because the same amount of vapours now occupy large space.
    (ii) Due to a sudden increase in volume, the pressure inside the sealed container suddenly decreases. According to Le-Chatelier’s principle for the equilibrium,
    stack Liquid left parenthesis l right parenthesis with left parenthesis less space volume right parenthesis below space space space leftwards harpoon over rightwards harpoon space space stack Vapour space left parenthesis straight g right parenthesis with left parenthesis more space volume right parenthesis below
    A decrease in pressure will shift the equilibrium in the forward direction. Thus the rate of evaporation will increase initially. The rate of condensation decreases initially because vapour pressure per unit volume decreases. However, due to increase in the rate of evaporation, the amount of vapour begins to increase and so the rate of condensation also begins to increase.
    (iii) When the equilibrium is again reached, the rate of evaporation becomes equal to the rate of condensation. The final vapour pressure will remain the same as vapour pressure before increasing the volume of the container. This is because the vapour pressure of a liquid does not depend on upon the amount of the liquid or the space above it but depends on only upon temperature.

    Question 54
    CBSEENCH11006353

    What are reversible and irreversible reactions? Give examples.

    Solution

    Reversible reactions: Reactions which proceed in both directions are called reversible reactions. In a reversible reaction, the reactants are changed into products and simultaneously the products are changed into reactants. A reversible reaction is shown by using two half arrows in opposite direction open parentheses leftwards harpoon over rightwards harpoon close parentheses.  In a reversible reaction, the reaction proceeding from left to right (reactants that give the products) is called forward reaction. The reaction proceeding from right to left (products that give back the reactants) is called a backwards reaction. The reversible reaction generally proceeds in a closed vessel. This prevents the escape of the products. Example of reversible reaction are:
    left parenthesis straight i right parenthesis space straight H subscript 2 plus straight I subscript 2 space space rightwards harpoon over leftwards harpoon space space 2 HI
left parenthesis ii right parenthesis space straight N subscript 2 plus 3 straight H subscript 2 space rightwards harpoon over leftwards harpoon space space 2 NH subscript 3
left parenthesis iii right parenthesis space 2 SO subscript 2 plus straight O subscript 2 space rightwards harpoon over leftwards harpoon space space 2 SO subscript 3
left parenthesis iv right parenthesis space space space PCl subscript 5 space rightwards harpoon over leftwards harpoon space space space space PCl subscript 3 plus Cl subscript 2
    Irreversible reactions: A chemical reaction is said to be irreversible if reactants are changed into products (proceeds only in the forward direction) but the products do not combine to form the reactants. These reactions are indicated by a single arrow left parenthesis rightwards arrow right parenthesis in a chemical equation. Examples of irreversible reactions are:
     (i) Burning of magnesium
               2 Mg space plus space straight O subscript 2 space space rightwards arrow space space 2 MgO
    (ii) Decomposition of potassium chlorate. 
    (iii) The reaction between hydrogen and oxygen to form water vapours. 
    2 straight H subscript 2 straight O space plus space straight O subscript 2 space space rightwards arrow from room space temp to Electric space spark of space 2 straight H subscript 2 straight O

    Question 55
    CBSEENCH11006354

    Write a short note on the concept of chemical equilibrium.

    Solution
    Consider a general reversible reaction
    straight A plus straight B rightwards harpoon over leftwards harpoon straight C plus straight D
    (reaction carried out in a closed vessel).
    In the beginning (i.e. at time t = zero), the concentrations of A and B are maximum and concentrations of C and D are equal to zero (as C and D are not formed). Hence at t = 0, the rate of forward reaction is maximum whereas the rate of backward reaction is minimum (almost equal to zero).

    As the time passes, A and B are consumed whereas more and more of C and D are formed. Hence, the concentration of A and B decreases while that of C and D increases. Since the reaction is carried out in a closed vessel, therefore, the products C and D also react back among themselves to give back the reactants. This means that the chemical reaction proceeds both ways and is called reversible reaction. Therefore, the rate of forward reaction falls off with time while the rate of the backward reaction gradually increases.
    Ultimately, a stage comes when the rate of the forward reaction becomes equal to the rate of backward reaction. The reaction is then said to be in a state of chemical equilibrium Thus, at equilibrium state, Rate of the forward reaction (Rf) = Rate of the backward reaction (Rb). The attainment of chemical equilibrium can be seen both in physical and chemical processes.
    Question 56
    CBSEENCH11006355

    How will you recognise the equilibrium state?

    Solution

    A reversible reaction is said to be in a state of equilibrium when the rate of the. forward reaction is equal to the rate of backward reaction. At equilibrium, the concentrations of the reactants and products remain constant provided the conditions under which the reaction is performed are not changed. Some observable properties (colour, concentration, partial pressure or density) of the reactants or products may be used to indicate the concentration of the reaction at equilibrium.
    For example, the colour of nitrogen dioxide (NO2) may be used in recognising the equilibrium state when the reaction takes place between carbon monoxide and nitrogen dioxide. During the reaction, the reddish brown colour of nitrogen dioxide slowly fades as it is changed to colourless nitric oxide. After some time, the intensity of the colour decreases and there will be no further change in colour. Then we can say that the equilibrium state is reached.
    stack NO subscript 2 with brown below space plus space CO space leftwards harpoon over rightwards harpoon space space NO plus CO subscript 2
    In the case of dissociation of calcium carbonate, the attainment of equilibrium is recognised by observing the constant partial pressure of carbon dioxide in the manometer.

    Question 57
    CBSEENCH11006356

    A reversible reaction attains equilibrium of dynamic nature. Explain.

    Solution
    A reversible reaction attains equilibrium of dynamic nature and not of static nature. The fact that the properties of a system become constant at the equilibrium stage may give the impression that both the forward and backward processes stop altogether. This, however, is not true. At equilibrium, the forward and backward reaction go at equal speeds, but do not stop. The rate of formation of the products exactly equals to the rate of formation of reactants again. As a result, the concentration of the reactants and products and other properties of the system remain unchanged. Thus the equilibrium is dynamic in nature.
    Question 58
    CBSEENCH11006357

    How will you demonstrate the dynamic nature of equilibrium state?

    Solution
    Take a vessel with a hole in it. 

    Plug the hole and fill it half with water from a water tap. Now remove the plug and simultaneously adjust the run in the tap so that the rates of out-flow and in-flow of water are equal. The level of water inside the vessel remains constant though water is flowing into and out of the vessel. This is a state of dynamic equilibrium.
    Question 59
    CBSEENCH11006358

    Comment on the statement: Equilibrium can be approached from either direction.

    Solution
    This can be proved experimentally by considering the equilibrium between nitrogen tetraoxide N2O4 ( a colourless gas) and nitrogen dioxide NO2 (a reddish brown gas).
    stack straight N subscript 2 straight O subscript 4 with Colourless with left parenthesis At space 273 space straight K right parenthesis below below space space space leftwards harpoon over rightwards harpoon space space space space stack 2 NO subscript 2 left parenthesis straight g right parenthesis with stack Reddish space brown with left parenthesis At space 373 space straight K right parenthesis below below
    It is observed that:
    (i) At 298K, the two gases exist as an equilibrium having a pale brown colour. 
    (ii) At 273K, N2O4 is stable and only exists as a colourless gas.
    (iii) At 373K, N2O4 decomposes completely into NO2 which is reddish brown in colour.
    Take two identical bulbs A and B with equal amounts of NO2 gas and seal them. Place bulb A in an ice bath and bulb B in boiling water. After some time, the gas in bulb A (placed in an ice bath) becomes colourless showing complete conversion of NO2 into N2O4. The gas in bulb B (placed in boiling water) has reddish brown colour showing completely NO2 gas.
    Now take out the bulbs A and B and transfer them to a water bath at 298K (at room temperature). The colour of the gas in bulb A starts changing into brown colour indicating the gradual conversion of N2O4 into NO2.
    straight N subscript 2 straight O subscript 4 left parenthesis straight g right parenthesis space space rightwards arrow space space space 2 NO subscript 2 left parenthesis straight g right parenthesis space space space space space space space space left parenthesis Bulb space straight A right parenthesis
    On the other hand, the colour of the gas in bulb B beings to fade and becomes pale indicating the gradual change of NO2 to N2O4.
    2 NO subscript 2 left parenthesis straight g right parenthesis space rightwards arrow space space space straight N subscript 2 straight O subscript 4 left parenthesis straight g right parenthesis space space space space space left parenthesis Bulb space straight B right parenthesis
    After some time when both the bulbs attain the temperature of the water bath (i.e. 298K), the colour in the two bulbs become identical and no further change in colour takes place. 

    This consistency of colour shows that the equilibrium has been attained in both the cases and both the bulbs contain a mixture of NO2 and N2O4 having the same composition. Thus, equilibrium can be approached from either direction.
    Question 60
    CBSEENCH11006359

    Describe in brief the characteristics of chemical equilibrium.

    Solution

    The important characteristics of chemical equilibrium are as follows:
    (i) At the equilibrium state, all the measurable properties such as concentration, colour, density, partial pressure become constant.
    (ii) Chemical equilibrium is dynamic in nature i.e. reaction does not stop but proceeds in both the directions with the same rate.
    (iii) Free energy change ∆G = 0.
    (iv) Chemical equilibrium can be approached from either direction (either from the reactants or products side).
    (v) Equilibrium can be reached only in a closed system.
    (vi) The equilibrium state is not affected by the presence of a catalyst as it lowers the same magnitude of activation energy by speeding up both forward and backward reactions to the same extent. However, a catalyst helps to reach the equilibrium state in a shorter period of time.


    Question 61
    CBSEENCH11006360

    Vapour pressures of water, acetone and ethanol at 293K are 2.34kPa, 12.36kPa and 5.85 kPa respectively. Which of these has the lowest and the highest boiling point? At 293K which of these evaporates least in a sealed container before equilibrium is established?

    Solution

    We know that when the temperature increases, the vapour pressure of a liquid also increases and at the boiling point, vapour pressure becomes equal to the atmospheric pressure. A liquid with lower vapour pressure will require a higher temperature for it to attain its vapour pressure equal to the atmospheric pressure. Therefore, the liquid with the highest vapour pressure will have the lowest boiling point. Acetone has the lowest boiling point and water has the highest boiling point.
    At 293K, water evaporates least in the sealed container before equilibrium is established.

    Question 62
    CBSEENCH11006361

    State and explain the law of mass action.

    Solution

    The law of mass action (Guldberg and Waage) may be stated as:
    The rate at which a substance reacts is directly proportional to its active mass (molar concentration) and the rate of chemical reaction is proportional to the product of active masses of the reacting substances.
    By the term active mass, we mean molar concentration or number of moles per litre. The active mass of A is denoted as [A].
    Consider a simple reaction A rightwards arrow Product
    According to the law of mass action,
    Rate of reaction proportional to open square brackets straight A close square brackets space equals space straight k open square brackets straight A close square brackets
    where [A] represents the active mass of A, k is proportionality constant known as velocity constant. The velocity constant is also called velocity co-efficient or rate constant or specific reaction rate.
    For space the space reaction semicolon space space straight A space plus space straight B space rightwards arrow space space space Products
    According to the law of mass action,
    Rate of the reaction proportional to space open square brackets straight A close square brackets space open square brackets straight B close square brackets space equals space straight k open square brackets straight A close square brackets space open square brackets straight B close square brackets
    For space straight a space reaction space 2 straight A plus straight B space rightwards arrow space space Products
or space space space space space straight A plus straight A plus straight B space rightwards arrow space space space Products
Rate space of space the space reaction space equals space straight k open square brackets straight A close square brackets space open square brackets straight A close square brackets space open square brackets straight B close square brackets
space space space space space space space space space space space space space space space space space space space space space space space space space space space equals straight k open square brackets straight A close square brackets squared open square brackets straight B close square brackets space space space space space space space space space space space space space space space space space space
    For a general reaction,
    aA plus bB plus cC space plus rightwards arrow space space Products
    According to the law of mass action, 
    Rate of the reaction = equals space straight k open square brackets straight A close square brackets to the power of straight a space open square brackets straight B close square brackets to the power of straight b space open square brackets straight C close square brackets to the power of straight c
    Hence the law of mass action may also be stated as the rate of the reaction is proportional to the product of the active masses (or molar concentration) of reactants with each active mass raised to the power equal to the number of molecules of the respective reactants participating in the reaction.

    Question 63
    CBSEENCH11006362

    Apply the law of mass action to a reversible reaction and state the law of chemical equilibrium.

    Solution
    Let us consider a simple reversible reaction in the state of equilibrium
                         straight A plus straight B rightwards harpoon over leftwards harpoon space space straight C plus straight D
    According to the law of mass action.
    Rate of the forward reaction open parentheses straight r subscript straight f close parentheses space proportional to space space open square brackets straight A close square brackets space open square brackets straight B close square brackets
    or         straight r subscript straight f space equals space straight k subscript straight f open square brackets straight A close square brackets open square brackets straight B close square brackets
    where kf is the rate constant for the forward reaction, [A] and [B] are molar concentrations of reactants A and B respectively.
    Rate of the backward reaction (rb) ∝ [C] [D] or rb = kb [C] [D]
    where kb is the rate constant for the backward reaction, [C] and [D] are molar concentrations of the products C and D respectively.
    At equilibrium:
                          Rate of the forward reaction open parentheses straight r subscript straight f close parentheses
                     = Rate of the backward reaction open parentheses straight r subscript straight b close parentheses
                              space space straight k subscript straight f open square brackets straight A close square brackets open square brackets straight B close square brackets space equals space straight k subscript straight b open square brackets straight C close square brackets open square brackets straight D close square brackets
    or                       straight k subscript straight f over straight k subscript straight b space equals space fraction numerator open square brackets straight C close square brackets space open square brackets straight D close square brackets over denominator open square brackets straight A close square brackets space open square brackets straight B close square brackets end fraction
                             straight K subscript straight c space equals space straight k subscript straight f over straight k subscript straight b fraction numerator open square brackets straight C close square brackets space open square brackets straight D close square brackets over denominator open square brackets straight A close square brackets open square brackets straight B close square brackets end fraction
    The constant straight K subscript straight c is called equilibrium constant and has a constant value at a given temperature. Similarly, for a reaction 2 straight A plus 2 straight B space rightwards harpoon over leftwards harpoon space space straight C plus straight D
    straight K subscript straight c space equals space fraction numerator open square brackets straight C close square brackets open square brackets straight D close square brackets over denominator open square brackets straight A close square brackets squared open square brackets straight B close square brackets cubed end fraction
    the above represents the complete expression for the law of chemical equilibrium. It may be defined as: For a reversible reaction at equilibrium, the ratio of the products of molar concentration of the products (substance formed) to the products of molar concentration of the reactants with each concentration term raised to a power equal to the number of moles of that substance in the balanced equation is constant at a given temperature.
    Question 65
    CBSEENCH11006364

    How is equilibrium constant expressed when the reaction is carried in the gaseous phase ?

    Solution
    When the reaction is carried in the gaseous phase, the equilibrium constant is expressed as To illustrate this, let us consider a purely gaseous reaction
    mA left parenthesis straight g right parenthesis space plus space nB left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space xC left parenthesis straight g right parenthesis space plus space yD left parenthesis straight g right parenthesis
    In this case, we shall consider the partial pressure of the gases to indicate their concentrations. The equilibrium constant (Kp) is expressed as
    straight K subscript straight p space equals space fraction numerator left parenthesis straight p subscript straight C right parenthesis to the power of straight X space cross times space left parenthesis straight p subscript straight D right parenthesis to the power of straight y over denominator left parenthesis straight p subscript straight A right parenthesis to the power of straight m space cross times space left parenthesis straight p subscript straight B right parenthesis to the power of straight n end fraction
    where PA, PB, PC and PD denote partial pressures of the respective gases.
    Question 66
    CBSEENCH11006365

    Derive the relation between Kp and Kc.

    Solution
    Consider a gaseous reaction in a state of equilibrium.
    aA plus bB space rightwards harpoon over leftwards harpoon space space cC left parenthesis straight g right parenthesis space plus space dD left parenthesis straight g right parenthesis
    Let PA, PB, Pc and pD be the partial pressures of A, B, C and D respectively at equilibrium, then
              straight K subscript straight p space equals space fraction numerator straight p subscript straight C space end subscript superscript straight c straight p subscript straight D superscript straight d over denominator straight p subscript straight A superscript straight a space cross times space straight p subscript straight B superscript straight b end fraction space space space space space space... left parenthesis 1 right parenthesis
    and  
      straight K subscript straight c space equals space fraction numerator open square brackets straight C close square brackets to the power of straight c space open square brackets straight D close square brackets to the power of straight d over denominator open square brackets straight A close square brackets to the power of straight a space open square brackets straight B close square brackets to the power of straight b end fraction    ...(2)
    We know that for an ideal gas,
                       PV = nRT
    or space space straight P space equals space straight n over straight V RT space equals space Molar space concentration space cross times space space RT
therefore space space space space space space space space straight p subscript straight A space equals space open square brackets straight A close square brackets space space RT
space space space space space space space space space space space straight p subscript straight B space equals open square brackets straight B close square brackets space RT
space space space space space space space space space space straight p subscript straight C space equals space open square brackets straight C close square brackets space RT
space space space space space space space space space space straight p subscript straight D space equals open square brackets straight D close square brackets space RT
    Substituting the value of partial pressure in equation (1),
      straight K subscript straight p space equals space fraction numerator open square brackets straight C close square brackets to the power of straight c space left parenthesis RT right parenthesis to the power of straight c space open square brackets straight D close square brackets to the power of straight d space left parenthesis RT right parenthesis to the power of straight d over denominator open square brackets straight A close square brackets to the power of straight a space left parenthesis RT right parenthesis to the power of straight a space open square brackets straight B close square brackets to the power of straight b space left parenthesis RT right parenthesis to the power of straight b end fraction
space space space space equals fraction numerator open square brackets straight C close square brackets to the power of straight c space open square brackets straight D close square brackets to the power of straight d space left parenthesis RT right parenthesis to the power of straight c plus straight d end exponent space over denominator open square brackets straight A close square brackets to the power of straight a space open square brackets straight B close square brackets to the power of straight b space left parenthesis RT right parenthesis to the power of straight a plus straight b end exponent end fraction
therefore space space space straight K subscript straight p space equals space straight K subscript straight c left parenthesis RT right parenthesis to the power of left parenthesis straight c plus straight d right parenthesis minus left parenthesis straight a plus straight b right parenthesis end exponent
                                                 
    [From equation (2)]
       or space space space straight K subscript straight p space equals space straight K subscript straight c left parenthesis RT right parenthesis to the power of increment straight n end exponent
where space increment straight n space equals space left parenthesis Total space number space of space moles space of space gaseous space products right parenthesis
space space space space space space space space space space minus left parenthesis Total space No. space of space moles space of space gaseous space reactants right parenthesis
straight R space equals space Gas space constant space left parenthesis 0.831 space litre space bar space straight K to the power of negative 1 end exponent space mol to the power of negative 1 end exponent right parenthesis
straight T space equals space Kelvin space temperature

    Question 67
    CBSEENCH11006366
    Question 68
    CBSEENCH11006367

    Write the expressions for equilibrium constant for the reactions:
    left parenthesis straight i right parenthesis space straight H subscript 2 left parenthesis straight g right parenthesis space plus space space straight I subscript 2 left parenthesis straight g right parenthesis space space space space space rightwards harpoon over leftwards harpoon space space 2 HI left parenthesis straight g right parenthesis
left parenthesis ii right parenthesis space straight N subscript 2 left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space 2 NH subscript 3 left parenthesis straight g right parenthesis
left parenthesis iii right parenthesis space PCl subscript 5 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space PCl subscript 3 left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis

    Solution

    Expression for equilibrium constant for the reactions:
    left parenthesis straight i right parenthesis space straight K subscript straight c space equals space fraction numerator open square brackets HI close square brackets squared over denominator open square brackets straight H subscript 2 close square brackets space open square brackets straight I subscript 2 close square brackets end fraction
left parenthesis ii right parenthesis space straight K subscript straight c space equals space fraction numerator open square brackets NH subscript 3 close square brackets cubed over denominator open square brackets straight N subscript 2 close square brackets space open square brackets straight H subscript 2 close square brackets cubed end fraction
left parenthesis iii right parenthesis space straight K subscript straight c space equals space fraction numerator open square brackets PCl subscript 3 close square brackets space open square brackets Cl subscript 2 close square brackets over denominator open square brackets PCl subscript 5 close square brackets end fraction

    Question 76
    CBSEENCH11006375

    Explain why pure liquids and solids can be ignored while writing the equilibrium constant expression?

    Solution

    The concentration of pure liquids and solids in the equilibrium expression for heterogeneous reactions are ignored because their concentrations remain constant. By convention, the concentration of all pure solids and pure liquids is taken as unity, i.e.
    [solid] = 1, [liquid] = 1.

    Question 77
    CBSEENCH11006376

    What is concentration quotient? Under what condition does it become equal to the equilibrium constant?

    Solution
    Concentration coefficient: The ratio of the product of concentrations of substances produced to that of reactants is known as concentration quotient. It is denoted by Q. For example, for a reversible reaction.
    straight A plus straight B rightwards harpoon over leftwards harpoon space straight C plus straight D
straight Q space equals space fraction numerator open square brackets straight C close square brackets space open square brackets straight D close square brackets over denominator open square brackets straight A close square brackets space open square brackets straight B close square brackets end fraction
    At equilibrium, Q becomes equal to K (equilibrium constant).
    Question 78
    CBSEENCH11006377

    What are the characteristics of equilibrium constant?

    Solution

    (i) The equilibrium constant has a definite value for every chemical reaction at a given temperature. However, it varies with the change in temperature.
    (ii) Its value is not influenced by the change in the concentration of reactants and products.
    (iii) It is not affected by the presence of a catalyst.
    (iv) The equilibrium constant for the forward reaction is the inverse of the equilibrium constant for the backward reaction.
    For    straight A plus straight B space rightwards harpoon over leftwards harpoon space straight C plus straight D
                   straight K space equals space fraction numerator open square brackets straight C close square brackets space open square brackets straight D close square brackets over denominator open square brackets straight A close square brackets space open square brackets straight B close square brackets end fraction
    and for
     straight C plus straight D space space rightwards harpoon over leftwards harpoon space space space straight A plus straight D
     straight K apostrophe space equals space fraction numerator open square brackets straight A close square brackets space open square brackets straight B close square brackets over denominator open square brackets straight C close square brackets space open square brackets straight D close square brackets end fraction
    Clearly  
        straight K equals space fraction numerator 1 over denominator straight K apostrophe end fraction

    (v) The value of K tells us the extent to which the forward or backward reaction has taken place. The Greater value of Kc and Kp means that the reaction has proceeded to a greater extent in the forward direction.
    (vi) The value of K changes if the coefficient of various species in the equation representing equilibrium are multiplied by the same number.
    For example,
      straight H subscript 2 space plus space straight I subscript 2 space space space rightwards harpoon over leftwards harpoon space space space 2 HI
    straight K subscript 1 space equals space fraction numerator open square brackets HI close square brackets squared over denominator open square brackets straight H subscript 2 close square brackets space open square brackets straight I subscript 2 close square brackets end fraction space equals space 49 space at space 711 straight K
    However, if we write 1 half straight H subscript 2 space plus space 1 half space leftwards harpoon over rightwards harpoon space HI
    Then straight K subscript 2 space equals space fraction numerator open square brackets HI close square brackets over denominator open square brackets straight H subscript 2 close square brackets to the power of 1 divided by 2 end exponent space open square brackets straight I subscript 2 close square brackets to the power of 1 divided by 2 end exponent end fraction
space space space space equals space square root of straight K space equals space square root of 49 space equals space 7

    Sponsor Area

    Question 80
    CBSEENCH11006379

    What are the units of equilibrium constant (Kc)?

    Solution
    The units of Kc vary from reaction to reaction.
    (i) Kc has no units when there is no change in a number of moles in a reaction.
    For space example comma space straight N subscript 2 plus straight O subscript 2 space rightwards harpoon over leftwards harpoon space space 2 NO
straight K subscript straight c space equals space fraction numerator open square brackets NO close square brackets over denominator open square brackets straight N subscript 2 close square brackets space open square brackets straight O subscript 2 close square brackets end fraction space equals space fraction numerator left parenthesis mol space straight L to the power of negative 1 end exponent right parenthesis squared over denominator left parenthesis mol space straight L to the power of negative 1 end exponent right parenthesis space left parenthesis mol space straight L to the power of negative 1 end exponent right parenthesis end fraction
    i.e. it is unitless.
    (ii) Kc has units when the number of moles in the reaction differs, e.g.
    straight N subscript 2 left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space 2 NH subscript 3 left parenthesis straight g right parenthesis
space straight K subscript straight c space equals space fraction numerator open square brackets NH subscript 3 close square brackets squared over denominator open square brackets straight N subscript 2 close square brackets space open square brackets straight H subscript 2 close square brackets cubed end fraction
space space space space space space space equals fraction numerator left parenthesis mol space straight L to the power of negative 1 end exponent right parenthesis squared over denominator left parenthesis mol space straight L to the power of negative 1 end exponent right parenthesis thin space left parenthesis mol space straight L to the power of negative 1 end exponent right parenthesis cubed end fraction
space space space space space space space space equals fraction numerator 1 over denominator left parenthesis mol space straight L to the power of negative 1 end exponent right parenthesis squared end fraction space equals space mol to the power of negative 2 end exponent space straight L squared
    Thus, straight K subscript straight c will have the units straight L squared space mol to the power of negative 2 end exponent.
    Question 82
    CBSEENCH11006381

    What is the significance of equilibrium constant?

    Solution

    (i) The numerical value of equilibrium constant is a measure of the extent to which reactants have been converted into the products. A large value of K indicates that reactants have been converted to the products to a large extent. The lower value of K indicates that only small amounts of reactants have been converted into products.

    (ii) If we know the initial concentration of reactants and equilibrium constant of the reaction, we can calculate the equilibrium concentration of various reactants and products.

    Question 83
    CBSEENCH11006382

    What qualitative information can you obtain from the magnitude of equilibrium constant?

    Solution
    The magnitude of the equilibrium constant (K) represents the extent to which a reaction can go. In other words, it is the measure of the completion of a reversible reaction. Larger the value of K, the greater will be the equilibrium concentration of the components on the right-hand side of a reaction relative to those on the left-hand side i.e. a reaction proceeds to a greater extent.
    Question 84
    CBSEENCH11006383

    A mixture of straight H subscript 2 comma space straight N subscript 2 space and space NH subscript 3 with molar concentration 3.0 space cross times space 10 to the power of negative 3 end exponent space mol space straight L to the power of negative 1 end exponent comma space 1.0 space cross times space 10 to the power of negative 3 end exponent space mol space straight L to the power of negative 1 end exponent and 2.0 space cross times space 10 cubed space mol space straight L to the power of negative 1 end exponent respectively was prepared at 500 K. At this temperature the value of straight K subscript straight c for reaction straight N subscript 2 left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 space rightwards harpoon over leftwards harpoon space space space 2 NH subscript 3 left parenthesis straight g right parenthesis comma space space is space 61. Predict whether at this state the concentration of NH subscript 3 will increases or decrease.

    Solution
    Reaction quotient, Qc for the reaction will be written as
    space straight Q subscript straight c space equals space fraction numerator open square brackets NH subscript 3 left parenthesis straight g right parenthesis close square brackets squared over denominator open square brackets straight N subscript 2 left parenthesis straight g right parenthesis close square brackets space open square brackets straight H subscript 2 left parenthesis straight g right parenthesis close square brackets cubed end fraction
space space space space space equals space fraction numerator left parenthesis 2.0 space cross times space 10 to the power of negative 3 end exponent right parenthesis squared over denominator left parenthesis 1.0 space cross times 10 to the power of negative 3 end exponent right parenthesis thin space left parenthesis 3.0 cross times 10 to the power of negative 3 end exponent right parenthesis cubed end fraction
space space space space space equals fraction numerator 4.0 space cross times space 10 to the power of negative 6 end exponent over denominator 27.0 space cross times space 10 to the power of negative 12 end exponent end fraction space equals 0.149 space cross times space 10 to the power of 6
space space space space space almost equal to space 1.5 space cross times space 10 to the power of 6
    Since Qc > Kc, so reaction will go in the left direction and ammonia decomposes into hydrogen and nitrogen.
    Question 85
    CBSEENCH11006384

    Equilibrium constant Kc for the reaction
                     straight N subscript 2 left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space 2 NH subscript 3 left parenthesis straight g right parenthesis space at space 500 space straight K space is space 0.061

    At a particular time, the analysis shows that composition of the reaction mixture is 3·0 mol L–1 N2, 2·0 mol L–1 H2 and 0·5 mol L–1 NH3. Is the reaction at equilibrium? If not in which direction does the reaction tend to proceed to reach equilibrium?

    Solution
    stack straight N subscript 2 left parenthesis straight g right parenthesis with 3.0 below space plus stack 3 straight H subscript 2 left parenthesis straight g right parenthesis with 2.0 below space rightwards harpoon over leftwards harpoon stack space 2 NH subscript 3 space left parenthesis straight g right parenthesis with 0.5 space conc. divided by mol space straight L to the power of negative 1 end exponent below
    Reaction quotient, Qc for the reaction will be written as
    straight Q subscript straight c space equals space fraction numerator open square brackets NH subscript 3 left parenthesis straight g right parenthesis close square brackets squared over denominator open square brackets straight N subscript 2 left parenthesis straight g right parenthesis close square brackets space open square brackets straight H subscript 2 left parenthesis straight g right parenthesis close square brackets cubed end fraction
space space space space space space equals space fraction numerator left parenthesis 0.5 right parenthesis squared over denominator left parenthesis 3.0 right parenthesis thin space left parenthesis 2.0 right parenthesis cubed end fraction space equals space 0.0104
    Given Kc 0.061< QC 0.0104

    Since Qc ≠ Kc, reaction is not in equilibrium.
    Since Qc < Kc reaction will proceed in the forward direction i.e. towards the formation of ammonia.

    Question 86
    CBSEENCH11006385

    The value of straight K subscript straight c for the reaction 2 straight A rightwards harpoon over leftwards harpoon space straight B plus straight C space is space 2 cross times space 10 to the power of negative 3 end exponent. At a given time the composition of reaction mixture is open vertical bar straight A close vertical bar space equals open vertical bar straight B close vertical bar space equals space open vertical bar straight C close vertical bar space equals space 3 space cross times space 10 to the power of negative 4 end exponent straight M. In which direction the reaction will proceed?

    Solution

    For the above reaction
                   straight Q subscript straight c space equals space fraction numerator open square brackets straight B close square brackets space open square brackets straight C close square brackets over denominator open square brackets straight A close square brackets squared end fraction      ...(1)
    Here,  
     open square brackets straight A close square brackets space equals space open square brackets straight B close square brackets space equals space open square brackets straight C close square brackets space equals space 3 cross times 10 to the power of negative 4 end exponent straight M comma
    Putting the values in expression (1), we have
             straight Q subscript straight C space equals space fraction numerator left parenthesis 3 cross times 10 to the power of negative 4 end exponent straight M right parenthesis left parenthesis 3 cross times 10 to the power of negative 4 end exponent straight M right parenthesis over denominator left parenthesis 3 cross times 10 to the power of negative 4 end exponent straight M right parenthesis squared end fraction space equals 1
    As Qc > Kc, so the reaction will proceed in the reverse direction.

    Question 87
    CBSEENCH11006386
    Question 88
    CBSEENCH11006387

    The reaction,
    CO left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 space rightwards harpoon over leftwards harpoon space space space CH subscript 4 left parenthesis straight g right parenthesis space plus space straight H subscript 2 straight O left parenthesis straight g right parenthesis is at equilibrium at 1300K in a 1 L flask. It also contains 0.30 mol of CO, 0.10 mol of H2 and 0.02 mol of H2O and an unknown amount of CH4 in the flask. Determine the concentration of CH4 in the mixture. The equilibrium constant, Kc, for the reaction at the given temperature is 3.90.

    Solution
    The given reversible reaction is
    CO left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space CH subscript 4 left parenthesis straight g right parenthesis plus space straight H subscript 2 straight O left parenthesis straight g right parenthesis
    Applying the law of chemical equilibrium
     space straight K subscript straight c space equals space fraction numerator open square brackets CH subscript 4 left parenthesis straight g right parenthesis close square brackets space open square brackets straight H subscript 2 straight O left parenthesis straight g right parenthesis close square brackets over denominator open square brackets CO left parenthesis straight g right parenthesis space open square brackets straight H subscript 2 left parenthesis straight g right parenthesis close square brackets close square brackets end fraction space... left parenthesis 1 right parenthesis
    Putting the values in expression (1), we have,
                     3.90 space equals space fraction numerator open square brackets CH subscript 4 left parenthesis straight g right parenthesis close square brackets space open square brackets 0.02 close square brackets over denominator left parenthesis 0.30 right parenthesis thin space left parenthesis 0.10 right parenthesis cubed end fraction
     [Molar conc  = No. of moles because volume of flask = 1L]
    or space space open square brackets CH subscript 4 left parenthesis straight g right parenthesis close square brackets space equals space fraction numerator 3.90 space cross times space 0.30 space cross times space left parenthesis 0.10 right parenthesis cubed over denominator 0.02 end fraction
space space space space space space space space space space space space space space space space space space space equals space 0.0585 space straight M
space space space space space space space space space space space space space space space space space space space space equals space 5.85 space cross times space 10 to the power of negative 2 end exponent straight M
    Question 89
    CBSEENCH11006388

    What is Kc for the following equilibrium when the equilibrium concentration of each substance
    is: open square brackets SO subscript 2 close square brackets space equals space 0.60 space straight M comma space space open square brackets straight O subscript 2 close square brackets space equals space 0.82 space straight M space and space open square brackets SO subscript 3 close square brackets space equals space 1.90 space straight M ? 
                         2 SO subscript 2 left parenthesis straight g right parenthesis space plus space straight O subscript 2 space space rightwards harpoon over leftwards harpoon space space 2 SO subscript 3 left parenthesis straight g right parenthesis

    Solution

    The reversible reaction is
                          space 2 SO subscript 2 plus straight O subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space 2 SO subscript 3 left parenthesis straight g right parenthesis
    The equilibrium constant Kc is given by
                   space straight K subscript straight c space equals space fraction numerator open square brackets SO subscript 3 close square brackets squared over denominator open square brackets SO subscript 2 close square brackets squared space open square brackets straight O subscript 2 close square brackets end fraction space space space space space space space space space space space... left parenthesis 1 right parenthesis
    Putting the values in expression (1), we have
       
     straight K subscript straight c space equals space fraction numerator left parenthesis 1.90 space straight M right parenthesis squared over denominator left parenthesis 0.60 space straight M right parenthesis squared space left parenthesis 0.82 space straight M right parenthesis end fraction
space space space equals space 12 space cross times space 229 space straight M to the power of negative 1 end exponent space space or space space space 12.229 space straight L space mol to the power of negative 1 end exponent

    Question 90
    CBSEENCH11006389

    One mole of H2O and one mole of CO are taken in a 10 L vessel and heated to 725K. At equilibrium, 40% of water (by mass) reacts with CO according to the equation

    straight H subscript 2 straight O left parenthesis straight g right parenthesis space plus space CO left parenthesis straight g right parenthesis space rightwards harpoon over leftwards harpoon space space straight H subscript 2 left parenthesis straight g right parenthesis space plus space CO subscript 2 left parenthesis straight g right parenthesis

    Calculate the equilibrium constant for the reaction.

    Solution
    The given reversible reaction is
    straight H subscript 2 straight O left parenthesis straight g right parenthesis space plus space CO space space rightwards harpoon over leftwards harpoon space straight H subscript 2 left parenthesis straight g right parenthesis space plus space CO subscript 2 left parenthesis straight g right parenthesis
    At equilibrium, the concentration of various species are
    open square brackets straight H subscript 2 straight O close square brackets space equals space fraction numerator 1 minus 0.40 over denominator 10 end fraction mol space straight L to the power of negative 1 end exponent space equals space 0.06 space mol space straight L to the power of negative 1 end exponent
open square brackets CO close square brackets space equals space 0.06 space mol space straight L to the power of negative 1 end exponent
open square brackets straight H subscript 2 close square brackets space equals space fraction numerator 0.4 over denominator 10 end fraction mol space straight L to the power of negative 1 end exponent space equals space 0.04 space mol space straight L to the power of negative 1 end exponent
open square brackets CO subscript 2 close square brackets space equals space 0.04 space mol space straight L to the power of negative 1 end exponent
    Applying the law of chemical equilibrium
             straight K space equals space fraction numerator open square brackets straight H subscript 2 left parenthesis straight g right parenthesis close square brackets space open square brackets CO subscript 2 left parenthesis straight g right parenthesis close square brackets over denominator space open square brackets straight H subscript 2 straight O left parenthesis straight g right parenthesis close square brackets space open square brackets CO left parenthesis straight g right parenthesis close square brackets end fraction space space space space space... left parenthesis 1 right parenthesis
    Putting the values in expression (1), we have,
             straight K space equals space fraction numerator 0.04 space cross times space 0.04 over denominator 0.06 space cross times space 0.06 space end fraction space space equals space 0.444
    Question 91
    CBSEENCH11006390

    A sample of HI(g) is placed in a flask at a pressure of 0·2 atm. At equilibrium, the partial pressure of HI(g) is 0·04 atm. What is Kp for the given equilibrium?

                          2 HI space left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space space space space straight H subscript 2 left parenthesis straight g right parenthesis space plus space straight I subscript 2 left parenthesis straight g right parenthesis

    Solution

    The given reversible reaction is 
                                   
    space space space space space space space space space space space space space space space space space space space space space space 2 HI left parenthesis straight g right parenthesis space rightwards harpoon over leftwards harpoon space space space space space space space space straight H subscript 2 left parenthesis straight g right parenthesis straight I space space space plus space straight I subscript 2 left parenthesis straight g right parenthesis
nitial space pressure space 0.2 space atm space space space space space space space space space space space space minus space space space space space space space space space space space space space minus
At space equilibrium space left parenthesis 0.2 minus straight p right parenthesis atm space space space space space space space straight p divided by 2 space atm space space space space space space straight p divided by 2 space atm
space space space space space space space space space space space space space space space space space space space space 0.04 space atm space space space space space space space space space space 0.08 space atm space space space space space 0.08 space atm
         (Decrease in the pressure of HI = 0.2 - 0.04  = 0.16 atm).
    Applying the law of chemical equilibrium
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#2 [internal function]: _hx_lambda->execute('Http Error #404')
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(532): call_user_func_array(Array, Array)
#4 [internal function]: haxe_Http_5(true, Object(com_wiris_plugin_impl_HttpImpl), Object(com_wiris_plugin_impl_HttpImpl), Array, Object(haxe_io_BytesOutput), true, 'Http Error #404')
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('haxe_Http_5', Array)
#6 [internal function]: _hx_lambda->execute('Http Error #404')
#7 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(27): call_user_func_array(Array, Array)
#8 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(444): com_wiris_plugin_impl_HttpImpl->onError('Http Error #404')
#9 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(458): haxe_Http->customRequest(true, Object(haxe_io_BytesOutput), NULL, NULL)
#10 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(40): haxe_Http->request(true)
#11 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(80): com_wiris_plugin_impl_HttpImpl->request(true)
#12 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#13 {main}</pre>
    Putting the values in expression (1), we have
                  straight K subscript straight p space equals space fraction numerator 0.08 space atm space cross times space 0.08 space atm over denominator left parenthesis 0.04 space atm right parenthesis squared end fraction space equals space 4.0
         

    Question 92
    CBSEENCH11006391

    At a certain temperature and total pressure of 105Pa, iodine vapour contains 40% by volume of I atoms
                      straight I subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space 2 straight I left parenthesis straight g right parenthesis

    Calculate straight K subscript straight p for the equlibrium.

    Solution

    The reversible reaction is,
             straight I subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space 2 straight I left parenthesis straight g right parenthesis
    Partial space pressure space of space straight I space atoms thin space left parenthesis straight p subscript 1 right parenthesis space equals space 40 over 100 cross times 10 to the power of 5 Pa space equals space 0.40 space cross times space 10 to the power of 5 Pa
Partial space pressure space of space straight I subscript 2 left parenthesis straight p subscript straight I subscript 2 end subscript right parenthesis space equals space 60 over 100 cross times 10 to the power of 5 Pa space equals space 0.60 space cross times space 10 to the power of 5 Pa
    Applying the law of chemical equilibrium
                         straight K subscript straight p space equals space straight p subscript straight I over straight p subscript straight I subscript 2 end subscript
    Putting the values, we have,
               straight K subscript straight p space equals space fraction numerator left parenthesis 0.40 space cross times space 10 to the power of 5 right parenthesis squared over denominator 0.60 space cross times space 10 to the power of 5 end fraction space equals space 2.67 space cross times space 10 to the power of 4
      

    Question 93
    CBSEENCH11006392

    The value of Kc for the reaction 3 straight O subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space 2 straight O subscript 3 left parenthesis straight g right parenthesis is 2.0 space cross times space 10 to the power of negative 50 end exponent at 25 degree straight C.  If the equilibrium concentration of straight O subscript 2 in air at 25 degree straight C is 1.6 space cross times space 10 to the power of negative 2 end exponent comma what is the concentration of O3?v 

    Solution

    The given reversible reaction is
                        3 straight O subscript 2 left parenthesis straight g right parenthesis space rightwards harpoon over leftwards harpoon space space space 2 straight O subscript 3 left parenthesis straight g right parenthesis
    Applying the law of chemical equilibrium
                         straight K subscript straight c space equals space open square brackets straight O subscript 3 left parenthesis straight g right parenthesis close square brackets squared over open square brackets straight O subscript 2 left parenthesis straight g right parenthesis close square brackets cubed                      ...(1)
    Putting this value in expression (1), we have
         
    2.0 space cross times space 10 to the power of negative 50 end exponent space equals space fraction numerator open square brackets straight O subscript 3 left parenthesis straight g right parenthesis close square brackets squared over denominator left parenthesis 1.6 space cross times space 10 to the power of negative 2 end exponent right parenthesis cubed end fraction
or space space space space open square brackets straight O subscript 3 left parenthesis straight g right parenthesis close square brackets squared space equals space left parenthesis 2.0 space cross times space 10 to the power of negative 50 end exponent right parenthesis space left parenthesis 1.6 space cross times space 10 to the power of negative 2 end exponent right parenthesis cubed
space space space space space space space space space space space space space space space space space space space equals space 8.192 space cross times space 10 to the power of negative 56 end exponent
or space space space open square brackets straight O subscript 3 left parenthesis straight g right parenthesis close square brackets space equals space 2.86 space cross times space 10 to the power of negative 28 end exponent straight M 
                            

    Question 94
    CBSEENCH11006393

    Calculate the value of equilibrium constant for the reaction:
    straight N subscript 2 left parenthesis straight g right parenthesis space plus space 2 straight O subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space 2 NO subscript 2 left parenthesis straight g right parenthesis semicolon space space space increment subscript straight r straight H to the power of 0 space equals space minus ve

    There is 10.0 mol of N2, 14·0 mol of O2 and 0·2 mol of NO2 present at equilibrium in a 3·0L vessel at 298K.What will be the effect of increased temperature on the equilibrium constant?

    Solution
    The reversible reaction is
    straight N subscript 2 left parenthesis straight g right parenthesis space plus space 2 straight O subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space 2 NO subscript 2 left parenthesis straight g right parenthesis semicolon space space space increment subscript straight r straight H to the power of 0 space equals space minus ve
    The equilibrium constant Kc is given by 
                         straight K subscript straight c space equals space fraction numerator open square brackets NO subscript 2 close square brackets squared over denominator open square brackets straight N subscript 2 close square brackets space open square brackets straight O subscript 2 close square brackets squared end fraction space space space space space space space space space space.... left parenthesis 1 right parenthesis
         open square brackets straight N subscript 2 close square brackets space equals space fraction numerator 10.0 space mol over denominator 3.0 space straight L end fraction space equals space 3.333 space mol space straight L to the power of negative 1 end exponent
open square brackets straight O subscript 2 close square brackets space equals space fraction numerator 14.0 space mol over denominator 300 space straight L end fraction space equals space 4.666 space mol space straight L to the power of negative 1 end exponent
open square brackets NO subscript 2 close square brackets space equals space fraction numerator 0.2 space mol over denominator 3.0 space straight L end fraction space equals space 0.666 space mol space straight L to the power of negative 1 end exponent
    Putting the values in expression (1), we have,
         straight K subscript straight c space equals space fraction numerator left parenthesis 0.666 space mol space straight L to the power of negative 1 end exponent right parenthesis squared over denominator left parenthesis 3.333 space mol space straight L to the power of negative 1 end exponent right parenthesis end fraction space left parenthesis 4.666 space mol space straight L to the power of negative 1 end exponent right parenthesis
space space space space equals space fraction numerator left parenthesis 0.666 right parenthesis squared over denominator left parenthesis 3.333 right parenthesis thin space left parenthesis 4.666 right parenthesis end fraction mol to the power of negative 1 end exponent space straight L
space space space space equals space space 6.1 space cross times 10 to the power of negative 5 end exponent space mol to the power of negative 1 end exponent straight L
    It is an exothermic reaction. According to Le-Chatterlier's principle, an increase in temperature would shift the equilibrium to left and the value of Kc should decrease.
    Question 95
    CBSEENCH11006394

    For the reaction
    SO subscript 2 left parenthesis straight g right parenthesis space plus space NO subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space SO subscript 3 left parenthesis straight g right parenthesis space plus space NO left parenthesis straight g right parenthesis the partial pressure of SO2, NO2, SO3 and NO at equilibrium are 0.5, 0.8, 0.7 and 1.2 bar respectively. Calculate Kp for the reaction. 



    Solution
    Reversible reaction at equilibrium is
    space SO subscript 2 left parenthesis straight g right parenthesis space plus NO subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space SO subscript 3 left parenthesis straight g right parenthesis space plus space NO left parenthesis straight g right parenthesis
    Applying the law of chemical equilibrium
                           straight K subscript straight p space equals space fraction numerator straight p subscript SO subscript 3 end subscript cross times straight p subscript NO over denominator straight p subscript SO subscript 2 end subscript space cross times space straight p subscript NO subscript 2 end subscript end fraction
    Substituting the values, we have,
                 straight K subscript straight p space equals space fraction numerator 0.7 space cross times space 1.2 over denominator 0.5 space cross times space 0.8 end fraction space equals space fraction numerator 0.84 over denominator 0.4 end fraction space equals space 2.1
    Question 96
    CBSEENCH11006395

    What are the types of chemical equilibrium?

    Solution
    There are two types of chemical equilibrium:
    (i) Homogeneous equilibrium: It is that equilibrium reaction in which all the reactants and products are in the same phase. For example
    left parenthesis straight i right parenthesis space straight H subscript 2 left parenthesis straight g right parenthesis space plus space straight I subscript 2 left parenthesis straight g right parenthesis space space space space space space space space rightwards harpoon over leftwards harpoon space space space space space 2 HI left parenthesis straight g right parenthesis
left parenthesis ii right parenthesis space straight N subscript 2 left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 left parenthesis straight g right parenthesis space space space space space rightwards harpoon over leftwards harpoon space space space space 2 NH subscript 3 left parenthesis straight g right parenthesis
left parenthesis iii right parenthesis space 2 SO subscript 2 left parenthesis straight g right parenthesis space plus space straight O subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space 2 SO subscript 3 left parenthesis straight g right parenthesis
    (ii) Heterogeneous equilibrium: It is that equilibrium reaction in which reactants and products are present in two or more phases, e.g. 
    left parenthesis straight i right parenthesis space 3 Fe left parenthesis straight s right parenthesis space plus space 4 straight H subscript 2 straight O left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space Fe subscript 3 straight O subscript 4 left parenthesis straight s right parenthesis space plus space 4 straight H subscript 2 left parenthesis straight s right parenthesis
left parenthesis ii right parenthesis space straight C left parenthesis straight s right parenthesis space plus space straight H subscript 2 straight O left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space CO left parenthesis straight g right parenthesis space plus space straight H subscript 2 left parenthesis straight g right parenthesis
left parenthesis iii right parenthesis space CaCO subscript 3 left parenthesis straight s right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space space CO left parenthesis straight s right parenthesis space plus space CO subscript 2 left parenthesis straight g right parenthesis
left parenthesis iv right parenthesis space space space Hgo left parenthesis straight s right parenthesis space space rightwards harpoon over leftwards harpoon space space Hg left parenthesis straight l right parenthesis space plus space 1 half straight O subscript 2 left parenthesis straight g right parenthesis
    Question 97
    CBSEENCH11006396

    Which of the following reactions involve homogeneous equilibria and which involve heterogeneous equilibria?

    left parenthesis straight a right parenthesis space 2 straight N subscript 2 straight O left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space 2 straight N subscript 2 left parenthesis straight g right parenthesis space plus space straight O subscript 2 left parenthesis straight g right parenthesis
left parenthesis straight b right parenthesis space space 2 NH subscript 3 left parenthesis straight g right parenthesis space rightwards harpoon over leftwards harpoon space space straight N subscript 2 left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 left parenthesis straight g right parenthesis
left parenthesis straight c right parenthesis space 2 Cu left parenthesis NO subscript 3 right parenthesis subscript 2 left parenthesis straight s right parenthesis space space rightwards harpoon over leftwards harpoon space space space 2 CuO left parenthesis straight s right parenthesis space plus space 4 NO subscript 2 left parenthesis straight g right parenthesis space plus space straight O subscript 2 left parenthesis straight g right parenthesis
left parenthesis straight d right parenthesis space Fe to the power of 3 plus end exponent left parenthesis aq right parenthesis space plus space 3 OH left parenthesis aq right parenthesis space rightwards harpoon over leftwards harpoon space space space Fe left parenthesis OH right parenthesis subscript 3 left parenthesis straight s right parenthesis

    Solution
    Homogeneous equilibria: (a) and (b)
    Heterogeneous equilibria: (c) and (d).
    Question 98
    CBSEENCH11006397

    Write the equilibrium constant expression for the following reactions:

    left parenthesis straight i right parenthesis space BaCO subscript 3 left parenthesis straight s right parenthesis space space rightwards harpoon over leftwards harpoon space space space space BaO left parenthesis straight s right parenthesis space plus space CO subscript 2 left parenthesis straight g right parenthesis
left parenthesis ii right parenthesis space AgBr left parenthesis straight s right parenthesis space space rightwards harpoon over leftwards harpoon space space space Ag to the power of plus left parenthesis aq right parenthesis space plus space Br to the power of minus left parenthesis aq right parenthesis
left parenthesis iii right parenthesis space Al left parenthesis straight s right parenthesis plus space 3 straight H to the power of plus left parenthesis aq right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space Al to the power of 3 plus end exponent left parenthesis aq right parenthesis space plus space 3 over 2 straight H subscript 2 left parenthesis straight g right parenthesis

    Solution
    left parenthesis straight i right parenthesis space BaCO subscript 3 left parenthesis straight s right parenthesis space space rightwards harpoon over leftwards harpoon space space space space BaO left parenthesis straight s right parenthesis space plus space CO subscript 2 left parenthesis straight g right parenthesis
space space space space space straight K subscript straight c space equals space fraction numerator open square brackets BaO left parenthesis straight s right parenthesis close square brackets space open square brackets CO subscript 2 left parenthesis straight g right parenthesis close square brackets over denominator open square brackets BaCO subscript 3 left parenthesis straight s right parenthesis close square brackets end fraction
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#2 [internal function]: _hx_lambda->execute('Http Error #404')
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(532): call_user_func_array(Array, Array)
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#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('haxe_Http_5', Array)
#6 [internal function]: _hx_lambda->execute('Http Error #404')
#7 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(27): call_user_func_array(Array, Array)
#8 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(444): com_wiris_plugin_impl_HttpImpl->onError('Http Error #404')
#9 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(458): haxe_Http->customRequest(true, Object(haxe_io_BytesOutput), NULL, NULL)
#10 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(40): haxe_Http->request(true)
#11 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(80): com_wiris_plugin_impl_HttpImpl->request(true)
#12 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#13 {main}</pre>

    Hence  straight K subscript straight c space equals space fraction numerator open square brackets BaO left parenthesis straight s right parenthesis close square brackets space open square brackets CO subscript 2 left parenthesis straight g right parenthesis close square brackets over denominator open square brackets BaCO subscript 3 left parenthesis straight s right parenthesis close square brackets end fraction
    By convention, open square brackets BaO left parenthesis straight s right parenthesis close square brackets space equals space 1 comma space space open square brackets BaCO subscript 3 left parenthesis straight s right parenthesis close square brackets space equals space 1
      Hence comma space straight K subscript straight c space equals space open square brackets CO subscript 2 left parenthesis straight g right parenthesis close square brackets
    For gases, using partial pressures,
    left parenthesis ii right parenthesis space AgBr left parenthesis straight s right parenthesis space space rightwards harpoon over leftwards harpoon space space space Ag to the power of plus left parenthesis aq right parenthesis space plus space Br to the power of minus left parenthesis aq right parenthesis
space space space space space space space space straight K subscript straight c space equals space fraction numerator open square brackets Ag to the power of plus left parenthesis aq right parenthesis close square brackets space open square brackets Br to the power of minus left parenthesis aq right parenthesis close square brackets over denominator open square brackets AgBr left parenthesis straight s right parenthesis close square brackets end fraction
    By convention,    open square brackets Ag space Br space left parenthesis straight s right parenthesis close square brackets space equals space 1
    Hence space straight K subscript straight c space equals space open square brackets Ag to the power of plus left parenthesis aq right parenthesis close square brackets space open square brackets Br to the power of minus left parenthesis aq right parenthesis close square brackets

    left parenthesis iii right parenthesis space Al left parenthesis straight s right parenthesis plus space 3 straight H to the power of plus left parenthesis aq right parenthesis space space rightwards harpoon over leftwards harpoon space space space Al to the power of 3 plus end exponent left parenthesis aq right parenthesis space plus space 3 over 2 straight H subscript 2 left parenthesis straight g right parenthesis
    space straight K subscript straight c space equals space fraction numerator open square brackets Al to the power of 3 plus end exponent left parenthesis aq right parenthesis close square brackets space open square brackets straight H subscript 2 left parenthesis straight g right parenthesis close square brackets to the power of 3 divided by 2 end exponent over denominator open square brackets Al left parenthesis straight s right parenthesis close square brackets space straight H squared left parenthesis aq right parenthesis right square bracket cubed end fraction
    By convention, open square brackets Al left parenthesis straight s right parenthesis close square brackets space equals space 1
    Hence straight K subscript straight c space equals space fraction numerator open square brackets Al to the power of 3 plus end exponent left parenthesis aq right parenthesis close square brackets space open square brackets straight H subscript 2 left parenthesis straight g right parenthesis close square brackets to the power of 3 divided by 2 end exponent over denominator open square brackets straight H to the power of plus left parenthesis aq right parenthesis close square brackets cubed end fraction

    Question 99
    CBSEENCH11006398

    State and explain Le-Chatelier’s principle.

    Solution

    Le-Chatelier’s principle. This principle may be stated as if a stress (such as a change in concentration, temperature or pressure) is applied to a system in equilibrium, the equilibrium shifts in a way to undo or nullify the effect of the imposed stress.
    (i) Effect of change of concentration on equilibrium. If the concentration of any one or all the reactants is increased, the equilibrium shifts towards right hand side to form more products whereas increase in the concentration of any one or all the products shifts the equilibrium towards left hand side to form more reactants in order to nullify the effect of increase in the concentration of reactants or products respectively. For example, consider the reaction,
    space space straight N subscript 2 left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space 2 NH subscript 3 left parenthesis straight g right parenthesis semicolon space
space increment subscript straight r straight H to the power of 0 space equals space minus 93.6 space kJ
    Increase in concentration of reactants (N2, H2) will shift the equilibrium in the forward direction in order to decrease their concentration. The addition of extra NH3 from outside the equilibrium mixture will shift the equilibrium in the backward direction.
    (ii) Effect of temperature on equilibrium. According to Le-Chatelier’s principle of increasing the temperature, the equilibrium shifts towards that direction where absorption of heat (endothermic change) takes place in order to nullify the effect of the rise in temperature. On the other hand, on decreasing the temperature, the equilibrium shifts towards that direction where the evolution of heat (exothermic change) takes place in order to nullify the effect of a decrease in temperature. For example.
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#13 {main}</pre>
    On decreasing the temperature, the equilibrium shifts in the forward direction i.e. towards the exothermic reaction (evolution of heat). Thus, a decrease in temperature favours the formation of sulphur trioxide.
    left parenthesis ii right parenthesis space space 2 SO subscript 2 left parenthesis straight g right parenthesis space plus space straight O subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space 2 SO left parenthesis straight g right parenthesis comma space space increment subscript straight r straight H to the power of 0 space equals space plus 180 space kJ
    On increasing the temperature, the equilibrium shifts in the forward direction i.e. towards the endothermic reaction (absorption of heat). Thus, an increase in the temperature favours the formation of nitric oxide.
    (iii) Effect of change in pressure on equilibrium. On increasing the pressure, the number of moles per unit volume increases and thus according to Le-Chatelier’s principle the equilibrium shifts towards the side where the number of moles per unit volume decreases in order to nullify the effect of an increase in pressure. For example.
    straight N subscript 2 left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space 2 NH subscript 3 left parenthesis straight g right parenthesis
    On increasing the pressure, the number of moles per unit volume increases and thus according to Le-Chaterlier's principle the equilibrium shifts towards the right-hand side (i.e. towards the formation of ammonia) where the number of moles per unit volume decreases.
    (iv) Effect of the catalyst. A catalyst has no effect on equilibrium point. This is because it increases the rate of the forward as well as backward reaction to the same extent. Thus, a catalyst does not affect the position of equilibrium, but simply helps to achieve the equilibrium in a shorter time i.e. quickly.

    Question 100
    CBSEENCH11006399

    With the help of Le-Chatelier’s principle, determine the favourable conditions of concentration, temperature and pressure for the reaction
    straight N subscript 2 left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space space 2 NH subscript 3 left parenthesis straight g right parenthesis semicolon space space increment subscript straight r straight H to the power of 0 space equals space minus 93.6 space kJ







    Solution

    straight N subscript 2 left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon from Endo to Exo of space space 2 NH subscript 3 left parenthesis straight g right parenthesis semicolon space space space increment subscript straight r straight H to the power of 0 space equals space minus 93.6 space kJ
    (i) Effect of concentration. Increase in concentration of reactants (N2, H2) will shift the equilibrium in the forward direction to form more ammonia in order to decrease their concentrations. The addition of extra NH3 from outside to the equilibrium mixture will shift the equilibrium in the backward direction. Thus, the addition of N2 and H2 favours the formation of ammonia.
    (ii) Effect of temperature. The forward reaction is exothermic in nature while the backward reaction is endothermic in nature. According to Le-Chatelier’s principle, on decreasing the temperature, the equilibrium shifts towards that direction where the evolution of heat takes place in order to nullify the effect of decreasing temperature. Thus, a decrease in temperature favours the formation of ammonia.
    On the other hand, on increasing the temperature the equilibrium shifts towards the backward direction where absorption of heat takes place in order to nullify the effect of the rise in temperature. Thus, lower temperature favours the formation of ammonia.
    (iii) Effect of pressure. On increasing the pressure, the number of moles per unit volume increases and thus according to Le-Chatelier’s principle, the equilibrium shifts towards that side where the number of moles per unit volume decreases in order to nullify the effect of an increase in pressure. On the other hand, on decreasing the pressure, the equilibrium shifts towards the backwards direction i.e. ammonia decomposes to give N2 and H2. Thus, an increase in pressure favours the formation of ammonia.
    Hence favourable conditions in the formation of ammonia are:
    (i) The addition of N2 and H2 
    (ii) Lower temperature
    (iii) Higher pressure.

    Question 101
    CBSEENCH11006400

    What is the effect of adding an inert gas(say He or N2):
    (i) at constant volume and
    (ii) at the constant pressure on the following equilibrium:

    PCl subscript 5 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space space PCl subscript 3 left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis

     

    Solution

    The given dissociation equilibrium is
       PCl subscript 5 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space space PCl subscript 3 left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis
               straight K subscript straight c space equals fraction numerator open vertical bar PCl subscript 3 close vertical bar space open vertical bar Cl subscript 2 close vertical bar over denominator open vertical bar PCl subscript 5 close vertical bar end fraction
    (i) Adding inert gas at constant volume. If an inert gas like helium or nitrogen etc. is added to a system at equilibrium at constant volume, then the total pressure increases. However, there will be no change in the position of equilibrium, even though the pressure has changed. This is because the concentrations of reactants and products (number of moles/volume) will not change. Hence the values of concentrations will continue to satisfy the equilibrium law. Hence the state of equilibrium will remain unaffected.
    (ii) Adding inert gas at constant pressure. When an inert gas is added to a system at equilibrium keeping the pressure constant, the volume of the system increases. This results in a decrease in a number of moles of reactants per unit volume. According to Le-Chatelier’s principle, the equilibrium shifts in a direction in which there is an increase in the number of moles of gases. Hence the equilibrium shifts towards the forward direction where the number of moles of gases increases. In other words, more PCldissociates to give PCl3 and Cl2. Hence dissociation of PCl5 increases with the addition of an inert gas.

    Question 102
    CBSEENCH11006401

    Does the number of moles of reaction products increase, decrease or remain the same when each of the following equilibria is subjected to a decrease in pressure by increasing the volume?
    left parenthesis straight a right parenthesis space PCl subscript 5 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space PCl subscript 3 left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis
left parenthesis straight b right parenthesis space CaO left parenthesis straight s right parenthesis space plus space CO subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space CaCO subscript 3 left parenthesis straight s right parenthesis
left parenthesis straight c right parenthesis space 3 Fe left parenthesis straight s right parenthesis space plus space 4 straight H subscript 2 straight O left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space Fe subscript 3 straight O subscript 4 left parenthesis straight s right parenthesis space plus space 4 straight H subscript 2 left parenthesis straight g right parenthesis

    Solution

    According to Le Chatelier’s principle, on decreasing the pressure, moles of reaction products will:
    (a) increase
    (b) decrease
    (c) remain the same.
    [∵ np = nr gaseous)

    Question 103
    CBSEENCH11006402

    Which of the following reactions will get affected by increasing the pressure? Also, mention whether the change will cause the reaction to go into forward or backward direction?

    left parenthesis straight i right parenthesis space COCl subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space space CO left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis
left parenthesis ii right parenthesis space CH subscript 4 left parenthesis straight g right parenthesis space plus space 2 straight S subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space CS subscript 2 left parenthesis straight g right parenthesis plus space 2 straight H subscript 2 straight S left parenthesis straight g right parenthesis
left parenthesis iii right parenthesis space CO subscript 2 left parenthesis straight g right parenthesis space plus space straight C left parenthesis straight s right parenthesis space space rightwards harpoon over leftwards harpoon space space 2 CO left parenthesis straight g right parenthesis
left parenthesis iv right parenthesis space 2 straight H subscript 2 left parenthesis straight g right parenthesis space plus space CO left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space CH subscript 3 OH left parenthesis straight g right parenthesis
left parenthesis straight v right parenthesis space CaCO subscript 3 left parenthesis straight s right parenthesis space rightwards harpoon over leftwards harpoon space space space CaO left parenthesis straight s right parenthesis plus space CO subscript 2 left parenthesis straight g right parenthesis
left parenthesis vi right parenthesis space 4 NH subscript 3 left parenthesis straight g right parenthesis space plus space 5 straight O subscript 2 left parenthesis straight g right parenthesis space rightwards harpoon over leftwards harpoon space space 4 NO left parenthesis straight g right parenthesis space plus space 6 straight H subscript 2 straight O left parenthesis straight g right parenthesis


    Solution

    (i) In this case np (=2) is greater than n(=1), the reaction will go in the backward direction.
    (ii) In this case np ( = 3) is equal to nr ( = 3), reaction will not be affected by the pressure.
    (iii) In this case np (= 2) is greater than n(=1), the reaction will go in the backward direction.
    (iv) In this case np (=1) is less than nr (= 3), the reaction will go in a forward direction.
    (v) In this case np (=1) is greater than nr (= 0) reaction will go in the backward direction.
    (vi) In this case np (= 10) is greater than nr (= 9), the reaction will go in the backward direction.

    Question 104
    CBSEENCH11006403

    Applying Le-Chatelier’s principle, predict the effect of pressure and temperature on the melting of ice.

    Solution
    The equilibrium may be represented as
    Ice with More space volume below space plus space Heat space space space leftwards harpoon over rightwards harpoon space space Water with Less space volume below

    The change of ice into water is a reversible endothermic (i.e. accompanied by absorption of heat) process. The reaction involves a decrease in volume. Hence according to Le-Chatelier’s principle:
    (i) With the increase in pressure: The equilibrium tends to shift in that direction in which there occurs a decrease in the volume. So in this case, an increase in pressure favours the conversion of ice into water.
    (ii) With the increase in temperature: The equilibrium shifts to the right i.e. towards the direction in which heat is absorbed. Thus, increase in temperature favours melting of ice.

    Question 105
    CBSEENCH11006404

    Applying Le-Chatelier’s principle, predict the effect of pressure and temperature on the evaporation of water (in a closed vessel).

    Solution
    The equilibrium may be represented as:
    Water with Less space volume below space plus space Heat space space space leftwards harpoon over rightwards harpoon space space space space stack Water space vapours with More space volume below
    The change of water to water vapours is a reversible endothermic (i.e. accompanied by absorption of heat) process. The reaction proceeds with the increase in volume. Hence according to Le-Chatelier’s principle:
    (i) With the increase in pressure, the equilibrium tends to shift in that direction in which there occurs a decrease in volume i.e. equilibrium shifts towards left. In other words, the increase in pressure favours the condensation of water vapours into water and decreasing pressure favours vaporisation of water into water vapours i.e. forward reaction is favourable.
    (ii) With the increase in temperature, the equilibrium shifts to the right i.e. towards the direction in which heat is absorbed. Thus, increase in temperature favours the vaporisation of water into water vapours.
    Question 106
    CBSEENCH11006405

    Applying Le-Chatelier’s principle predict the effect of temperature on the solubility of solid substances.

    Solution
    Certain salts like ammonium chloride dissolve with the absorption of heat (endothermic reaction). Such reactions can be represented as:
    Solute space plus space Solvent space rightwards harpoon over leftwards harpoon space space Solution semicolon space space increment subscript straight r straight H to the power of 0 space equals space plus ve
NH subscript 4 Cl left parenthesis straight s right parenthesis space plus water space rightwards harpoon over leftwards harpoon space space NH subscript 4 left parenthesis aq right parenthesis space plus space Cl to the power of minus left parenthesis aq right parenthesis semicolon space increment subscript straight r straight H to the power of 0 space equals space plus ve
    According to Le-Chatelier’s principle, on increasing temperature, the equilibrium shifts towards that direction where absorption of heat (endothermic change) takes place in order to nullify the effect of the rise in temperature. Hence solubility of such salts increases with the increase in temperature.
    On the other hand, certain salts like sodium hydroxide dissolve with the evolution of heat. The equilibrium may be represented as:
    Solute space plus space Solvent space space rightwards harpoon over leftwards harpoon space space space Solution semicolon space increment subscript straight r straight H to the power of 0 space equals space minus ve
NaOH left parenthesis straight s right parenthesis space plus space straight H subscript 2 straight O space rightwards harpoon over leftwards harpoon space space Na to the power of plus left parenthesis aq right parenthesis space plus space OH to the power of minus left parenthesis aq right parenthesis semicolon space increment subscript straight r straight H to the power of 0 space equals space minus ve
    Applying Le-Chatelier’s principle, on increasing temperature, the equilibrium shifts towards that direction where absorption of heat takes place i.e. backwards reaction favours. Hence, the solubility of such salts decreases with the rise in temperature.
    Question 107
    CBSEENCH11006406

    Applying Le-Chatelier’s principle, predict the effect of temperature and pressure on the solubility of gas.

    Solution
    Dissolution of gas is an exothermic process. The equilibrium may be represented as:
    Gas + Solvent  rightwards harpoon over leftwards harpoon  Solution;  increment subscript straight r straight H to the power of 0 space equals space minus ve
    According to Le-Chatelier's principle:
    (i) With the increase of temperature, the equilibrium shifts towards that direction where absorption of heat takes place in order to nullify the effect of the rising in temperature. In such case, the equilibrium will shift in the backward direction i.e., the solubility decreases.
    (ii) With the increase of pressure, the volume is reduced. Consequently, the system proceeds in a direction in which the pressure of the gas decreases and therefore, some of the gas dissolves in solution. Thus, an increase in pressure increases the solubility of a gas in liquids while a decrease in pressure reduces the solubility.

    Question 108
    CBSEENCH11006407

    Dihydrogen gas is obtained from natural gas by partial oxidation with steam as per following endothermic reaction:

    CH subscript 4 left parenthesis straight g right parenthesis space plus space straight H subscript 2 straight O left parenthesis straight g right parenthesis space space leftwards harpoon over rightwards harpoon space CO left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 left parenthesis straight g right parenthesis

    (a) Write an expression for Kp for the above reaction.
    (b) How will the values of Kp and composition of equilibrium mixture be affected by:
    (i) increasing the pressure
    (ii) increasing the temperature
    (iii) using a catalyst?


    Solution

    (a) straight K subscript straight p space equals space fraction numerator straight p subscript CO space cross times straight p subscript straight H subscript 2 end subscript superscript 3 over denominator straight p subscript CH subscript 4 end subscript space cross times space straight p subscript straight H subscript 2 straight O end subscript end fraction

    (b)
    (i) The value of Kp remains unchanged on increasing the pressure. According to Le Chatelier’s principle, equilibrium will shift in the backward direction.
    (ii) In case of endothermic reactions the value of increases with the increase in temperature. According to Le Chatelier principle, equilibrium will shift in the forward direction.
    (iii) Kp will remain undisturbed i.e. equilibrium composition will not be disturbed but equilibrium will be attained equally.However, in the presence of a catalyst, the equilibrium would be attained quickly.

    Question 109
    CBSEENCH11006408

    Describe the effect of:
    (a) addition of H2
    (b) addition of CH3OH
    (c) removal of CO
    (d) removal of CH3OH
    on the equilibrium of the reaction:

          2 straight H subscript 2 left parenthesis straight g right parenthesis space plus space CO left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space CH subscript 3 OH left parenthesis straight g right parenthesis

    Solution

    (a) According to Le-Chatelier’s principle, equilibrium will shift in the forward direction.
    (b) According to Le-Chatelier’s principle, equilibrium will shift in the backward direction.
    (c) According to Le-Chatelier’s principle, equilibrium will shift in the backward direction.
    (d) According to Le-Chatelier’s principle, equilibrium will shift in the forward direction.

    Question 110
    CBSEENCH11006409

    At 473K, equilibrium constant Kfor decomposition of phosphorus pentachloride, PCl5 is 8·3 × 10–3. If decomposition is depicted as

    PCl subscript 5 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space PCl subscript 3 left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis comma space space increment subscript straight r straight H to the power of 0 space equals space 124.0 space kJ space mol to the power of negative 1 end exponent

    (a) write an expression for Kc for the reaction.

    (b) what is the value of Kc for the reverse reaction at the same temperature?

    (c) what would be the effect on K
    c if:
    (i) more PCl5 is added
    (ii) pressure is increased
    (iii) temperature is increased? 

    Solution
    left parenthesis straight a right parenthesis space straight K subscript straight c space equals space fraction numerator open square brackets PCl subscript 3 close square brackets space open square brackets Cl subscript 2 close square brackets over denominator open square brackets PCl subscript 5 close square brackets end fraction space equals space 8.3 space cross times 10 to the power of negative 3 end exponent
    (b) Kc for reverse reaction
        equals space fraction numerator 1 over denominator straight K subscript straight c space for space forward space observation end fraction
equals space fraction numerator 1 over denominator 8.3 space cross times space 10 to the power of negative 3 end exponent end fraction space equals space 120.48

    (c)
    (i) Kc remains unchanged when more PClis added.
    (ii) When pressure is increased, Kc remains unchanged.
    (iii) As given reaction is endothermic, on increasing the temperature, Af will increase.
    As straight K subscript straight c space equals space straight k subscript straight f over straight k subscript straight b comma space straight K subscript straight c  will increase with the increase of temperature.

    Question 111
    CBSEENCH11006410

    Bromine water (a dilute solution of bromine in water) is brown and weakly acidic because of the equilibrium denoted by the equation:

    Br subscript 2 left parenthesis aq right parenthesis space plus space straight H subscript 2 straight O left parenthesis straight l right parenthesis space space rightwards harpoon over leftwards harpoon space space space HBrO left parenthesis aq right parenthesis space plus space straight H subscript 3 straight O to the power of plus left parenthesis straight l right parenthesis space plus space Br to the power of minus left parenthesis aq right parenthesis

    In solution, Br–(aq) is brown, Br– is colourless and HBrO (hypobromic acid –a weak acid) is colourless. When sodium hydroxide is added to the solution, the solution becomes colourless but the colour returns when hydrochloric acid is added. Explain the observation.

    Solution
    The equilibrium reaction is
    stack Br subscript 2 left parenthesis aq right parenthesis with left parenthesis Brown right parenthesis below space plus space straight H subscript 2 straight O left parenthesis straight l right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space stack HBrO left parenthesis aq right parenthesis with left parenthesis Colourless right parenthesis below space plus space straight H subscript 3 straight O to the power of plus left parenthesis straight l right parenthesis space plus space Br to the power of minus left parenthesis aq right parenthesis
    (i) When NaOH is added to the solution, it combines with the acid HBrO forming NaBrO (sodium hypobromite) and water both of which are colourless.
                          HBrO space plus space NaOH space space rightwards arrow space space NaBrO space plus space straight H subscript 2 straight O
    Also, OH to the power of minus ions (from NaOH) combine with straight H subscript 3 straight O to the power of plus ions to form colourless water.
                             OH to the power of minus plus straight H subscript 3 straight O to the power of minus space space space rightwards arrow space space space 2 straight H subscript 2 straight O space space space... left parenthesis 2 right parenthesis
    Both these reactions (1) and (2) shift the equilibrium in the forward direction where the substances are colourless.
    (ii) The addition of HCl acid gives H3O+ ions. This shifts the equilibrium backward forming more of Br2 which gives a brown colour to the solution.
    Question 112
    CBSEENCH11006411

    For the exothermic formation of sulphur trioxide from sulphur dioxide and oxygen in gas phase
              space space space space space 2 SO subscript 2 left parenthesis straight g right parenthesis space plus space straight O subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space 2 SO subscript 3 left parenthesis straight g right parenthesis
straight K subscript straight p space equals space 40.5 space atm to the power of negative 1 end exponent space at space 900 straight K space and space increment subscript straight r straight H to the power of 0 space equals space minus 198 space kJ

    (i) write the expression for the equilibrium constant for the reaction;
    (ii) at room temperature (300 K) will Kp be greater than, less than or equal to Kp at 900 K;
    (iii) how will the equilibrium be affected if the volume of the vessel containing the three gases is reduced, keeping the temperature constant; what happens;
    (iv) what is the effect of adding 1 mole He(g) to a flask containing SO2,O2 and SO3 at equilibrium at constant temperature?

    Solution
    (i) The chemical equation for the reaction is
                 2 SO subscript 2 left parenthesis straight g right parenthesis space plus space straight O subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space 2 SO subscript 3 left parenthesis straight g right parenthesis
    The expression for the equilibrium constant is
    straight K subscript straight p space equals space fraction numerator straight p subscript SO subscript 3 end subscript superscript 2 over denominator straight p squared subscript SO subscript 2 end subscript space cross times space space straight p subscript straight O subscript 2 end subscript end fraction space space space space or space space space space straight K subscript straight c space equals space fraction numerator open square brackets SO subscript 3 close square brackets squared over denominator open square brackets SO subscript 2 close square brackets squared space open square brackets straight O subscript 2 close square brackets end fraction
    (ii) The forward reaction is exothermic in nature i.e. accompanied by the evolution of heat. By decreasing the temperature (from 900K to 300K), then according to Le-Chatelier’s principle, the equilibrium shifts towards the forward direction where the evolution of heat takes place in order to nullify the effect of a decrease in temperature. This means that partial pressure of SO3(g) will increase while those of SO2(g) and O2(g) decreases. Hence Kp will increase by decreasing the temperature.
    (iii) By decreasing the volume, the number of molecules per unit volume will increase. According to Le-Chatelier’s principle, the equilibrium shifts towards that side where the number of moles per unit volume decreases. Thus, the speed of forward reaction will increase. Therefore, the molar concentration of SO3(g) will increase.
    (iv) Helium is an inert gas and does not react with either the reactants or products. Therefore, the partial pressures of the gases will remain same on adding one mole of helium as the volume of the flask is fixed. Hence the equilibrium will remain unaffected.
    Question 113
    CBSEENCH11006412

    The dissociation of phosgene is represented as follows:

    COCl subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space CO left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis

    When the mixture of these three gases is compressed at constant temperature, what happens to:
    (i) the amount of CO in the mixture.
    (ii) the partial pressure of COCl2
    (iii) the equilibrium constant for the reaction?

    Solution
    COCl subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space space CO left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis
    (i) The forward reaction is accompanied by the increase of pressure. If the pressure of the equilibrium mixture is increased at constant temperature then according to Le-Chatelier’s principle, the equilibrium will shift in the backward direction i.e. the amount of CO in the mixture will decrease.
    (ii) As the equilibrium shifts in the backward direction, the partial pressure of COCl2will increase.
    (iii) For the reaction
       COCl subscript 2 left parenthesis straight g right parenthesis space rightwards harpoon over leftwards harpoon space space CO left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis
straight K space equals space fraction numerator open square brackets CO close square brackets space open square brackets Cl subscript 2 close square brackets over denominator open square brackets COCl subscript 2 close square brackets end fraction
    As [CO] and [Cl2] decrease and [COCl2] increases, the value of equilibrium constant K will decrease.
    Question 114
    CBSEENCH11006413

    For the equilibrium 2 NOCl left parenthesis straight g right parenthesis space rightwards harpoon over leftwards harpoon space space space 2 NO left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis the value of the equilibrium constant KC is 3.75 space cross times space 10 to the power of negative 6 end exponent space space at space 1069 space straight K.  Calculate Kfor the reaction at this temperature.


    Solution
    The reversible reaction is
                         2 NOCl left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space 2 NO left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis
    We know, 
                        straight K subscript straight p space equals space straight K subscript straight c left parenthesis RT right parenthesis to the power of increment straight n end exponent                 ...(1)
    Here,            straight K subscript straight C space equals space 3.75 space cross times space 10 to the power of negative 6 end exponent semicolon
                       straight R space equals space 0.0831 thin space straight L space bar space straight K to the power of negative 1 end exponent space mol to the power of negative 1 end exponent
straight T space equals space 1069 space straight K semicolon space increment straight n space equals space left parenthesis 2 plus 1 right parenthesis minus 2 space equals space 1
    Substituting the value in eq. (1), we have,
                        
    straight K subscript straight p space equals space 3.75 space cross times space 10 to the power of negative 6 end exponent left parenthesis 0.0831 space cross times space 1069 right parenthesis
space space space space space equals space 3.33 space cross times space 10 to the power of negative 2 end exponent
    Question 115
    CBSEENCH11006414

    For the equilibrium
    2 NOC l left parenthesis straight g right parenthesis space space space space rightwards harpoon over leftwards harpoon space space space space 2 NO left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis
    the value of the constant, Kis 3.75 space cross times space 10 to the power of negative 6 end exponent space at space 1069 space straight K. Calculate straight K subscript straight p for the reaction at this temperature.
        

    Solution

    We know
                         straight K subscript straight p space equals space straight K subscript straight c left parenthesis RT right parenthesis to the power of increment straight n end exponent                  ...(1)

         Here space increment straight n space equals space straight n subscript straight p space minus space straight n subscript straight r space equals space left parenthesis 2 plus 1 right parenthesis minus 2 space equals space 1
space space space space space space space space straight K subscript straight c space equals space 3.75 space cross times space 10 to the power of negative 6 end exponent
space space space space space space space space space straight T space equals space 1069
                straight R space equals 0.0831 space bar space straight L space mol to the power of negative 1 end exponent straight K to the power of negative 1 end exponent
    Putting the values in expression (1), we have
       
        straight K subscript straight p space equals space left parenthesis 3.75 space cross times space 10 to the power of negative 6 end exponent right parenthesis space left parenthesis 0.0831 right parenthesis cross times left parenthesis 1069 right parenthesis
space space space space equals space 0.033

    Question 116
    CBSEENCH11006415

    The value of Kc for the reaction CO left parenthesis straight g right parenthesis space plus space 2 straight H subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space CH subscript 3 OH left parenthesis straight g right parenthesis is found to be 186.9 at 750K. Calculate the value of straight K subscript straight p comma if partial pressures are expressed in bars.
            

    Solution
    The reversible reaction is
                     CO left parenthesis straight g right parenthesis space plus space 2 straight H subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space CH subscript 3 OH left parenthesis straight g right parenthesis
    We know,     straight K subscript straight P space equals space straight K subscript straight c left parenthesis RT right parenthesis to the power of increment straight n end exponent                   ...(1)
    Now,            straight K subscript straight c space equals space 186.9 space
                        straight R space equals space 0.0821 space straight L space bar space straight K to the power of negative 1 end exponent space mol to the power of negative 1 end exponent
straight T space equals space 750 space straight K semicolon space space space space increment straight n space equals space 1 minus left parenthesis 1 plus 2 right parenthesis space equals space minus 2
    Substituting the value in equation (1), we have,
        straight K subscript straight p space equals space 186.9 space cross times space left parenthesis 0.0821 space cross times 750 right parenthesis to the power of negative 2 end exponent
space space space space space equals space fraction numerator 186.9 over denominator left parenthesis 0.0821 right parenthesis thin space left parenthesis 750 right parenthesis squared end fraction 0.0494
    Question 117
    CBSEENCH11006416

    Find out the value of Kc for each of the following equilibrium from the value of Kp:

    left parenthesis straight a right parenthesis space 2 space NOCl left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space 2 NO left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis semicolon space space straight K subscript straight p space equals space 1.8 space cross times space 10 to the power of negative 2 end exponent space at space 500 straight K
left parenthesis straight b right parenthesis space CaCO subscript 3 left parenthesis straight s right parenthesis space space space space leftwards harpoon over rightwards harpoon space space CaO left parenthesis straight s right parenthesis space plus space CO subscript 2 left parenthesis straight g right parenthesis comma space straight K subscript straight p space equals space 167 space at space 1073 space straight K

    Solution
    (a) The reversible reaction is
            2 NOCl left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space space 2 NO left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis
    We know, 
                  straight K subscript straight p space equals space straight K subscript straight c left parenthesis RT right parenthesis to the power of increment straight n end exponent
    or space space space space straight K subscript straight c space equals space fraction numerator straight K subscript straight p over denominator left parenthesis RT right parenthesis to the power of increment straight n end exponent end fraction                           ...(1)
    Here,    
     straight K subscript straight p space equals space 1.8 space cross times space 10 to the power of negative 2 end exponent semicolon
                 
     straight R space equals space 0.00831 space straight L space bar space straight K to the power of negative 1 end exponent space mol to the power of negative 1 end exponent
straight T space equals space 500 space straight K semicolon
increment straight n space equals space left parenthesis 2 plus 1 right parenthesis minus 2 space equals space 1
    Substituting the values in (1), we have,
                   straight K subscript straight c space equals fraction numerator 1.8 space cross times 10 to the power of negative 2 end exponent over denominator 0.0831 space cross times 500 end fraction space equals space 4.33 space cross times space 10 to the power of 4
    (b) The reversible reaction is
        CaCO subscript 3 left parenthesis straight s right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space CaO left parenthesis straight s right parenthesis space plus space CO subscript 2 left parenthesis straight g right parenthesis
    We know, 
                straight K subscript straight p space equals space straight K subscript straight c left parenthesis RT right parenthesis to the power of increment straight n end exponent
    or space space space space straight K subscript straight c space equals space fraction numerator straight K subscript straight p over denominator left parenthesis RT right parenthesis to the power of increment straight n end exponent end fraction                   ...(1)
    Here space straight K subscript straight p space equals space 167 semicolon space space straight R space equals space 0.0831 space straight L space bar space straight K to the power of negative 1 end exponent space mol to the power of negative 1 end exponent
straight T space equals space 1073 space straight K semicolon space space increment straight n space equals space 1
    Substituting the values in (1), we have, 
     straight K subscript straight c space equals space fraction numerator 167 over denominator 0.0831 space cross times space 1073 space end fraction space equals space 1.87

    Question 118
    CBSEENCH11006417

    At 700K, the equilibrium constant Kp, for the reaction
       2 SO subscript 3 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space 2 SO subscript 2 left parenthesis straight g right parenthesis space plus space straight O subscript 2 left parenthesis straight g right parenthesis is 1.8 space cross times space 10 to the power of negative 3 end exponent space straight k space Pa. What is the chemical value in moles per litre of Kfor this reaction at the same temperature?

    Solution
    The reversible reaction is
    2 SO subscript 3 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space space 2 SO subscript 2 left parenthesis straight g right parenthesis space plus space straight O subscript 2 left parenthesis straight g right parenthesis
    We know,
     straight K subscript straight p space equals space straight K subscript straight c left parenthesis RT right parenthesis to the power of increment straight n end exponent
      increment straight n space equals space left parenthesis 2 plus 1 right parenthesis space minus 2 space equals space 1
straight T space equals space 700 space straight K semicolon space space space straight K subscript straight p space equals space 1.8 space cross times space 10 to the power of negative 3 end exponent KP subscript straight a
straight K subscript straight p space equals space fraction numerator 1.8 space cross times 10 to the power of negative 3 end exponent KP subscript straight a over denominator 101.3 space straight K space Pa space atm to the power of negative 1 end exponent end fraction space equals space 1.78 space cross times space 10 to the power of negative 5 end exponent atm
    Now,   
    Now space straight K subscript straight c space equals space fraction numerator straight K subscript straight p over denominator left parenthesis RT right parenthesis to the power of increment straight n end exponent end fraction
    Substituting the values, we have,
    straight K subscript straight c space equals space fraction numerator 1.78 space cross times space 10 to the power of negative 5 end exponent atm over denominator 0.082 space straight L space atm space straight K to the power of negative 1 end exponent space mol to the power of negative 1 end exponent space cross times space 700 space straight K end fraction
           equals 3.09 cross times 10 to the power of negative 7 end exponent mol space straight L to the power of negative 1 end exponent
    Question 119
    CBSEENCH11006418

    At 450K, Kp = 2·0 × 1010/bar for the given reaction at equilibrium:
                   2 SO subscript 2 left parenthesis straight g right parenthesis space plus space straight O subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space 2 SO subscript 3 left parenthesis straight g right parenthesis

    What is Kc at this temperature?

    Solution
    The reversible reaction is
    2 SO subscript 2 left parenthesis straight g right parenthesis space plus space straight O subscript 2 left parenthesis straight g right parenthesis space rightwards harpoon over leftwards harpoon space space 2 SO subscript 3 left parenthesis straight g right parenthesis       
    We know, 
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#13 {main}</pre>                       ...(1)  
    space Here comma space space increment straight n space equals space 2 minus 3 space equals space minus 1
space space space space space space space space space space space space space straight T space equals space 450 space straight K
space space space space space space space space space space straight K subscript straight p space equals space 2.0 space cross times space 10 to the power of 10 space bar to the power of negative 1 end exponent
       Putting the values in expression (1), we have
                  2.0 space cross times space 10 to the power of negative 10 end exponent bar to the power of negative 1 end exponent space equals space straight K subscript straight c left parenthesis RT right parenthesis to the power of increment straight n end exponent
    therefore space space space straight K subscript straight c space equals space 2.0 space cross times space 10 to the power of negative 10 end exponent bar to the power of negative 1 end exponent space left parenthesis RT right parenthesis to the power of negative increment straight n end exponent
space space space space space space space space space space space equals space 2.0 space cross times space 10 to the power of negative 10 end exponent space bar to the power of negative 1 end exponent left parenthesis RT right parenthesis
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space increment straight n space equals space minus 1 close square brackets space space space space space space space space space space space space space space space space space space space space space space space space space
space
             equals space 2.0 space cross times space 10 to the power of negative 10 end exponent bar to the power of negative 1 end exponent left parenthesis 0.0831 space straight L space bar space straight K to the power of negative 1 end exponent space mol to the power of negative 1 end exponent right parenthesis space left parenthesis 450 space straight K right parenthesis
equals space 7.48 space cross times space 10 to the power of 11 straight L space mol to the power of negative 1 end exponent

    Sponsor Area

    Question 120
    CBSEENCH11006419

    The equilibrium constant at 278K for Cu left parenthesis straight s right parenthesis space plus space 2 Ag to the power of plus left parenthesis aq right parenthesis space rightwards harpoon over leftwards harpoon space space space Cu to the power of 2 plus end exponent left parenthesis aq right parenthesis space plus space 2 Ag left parenthesis straight s right parenthesis is 2.0 space cross times space 10 to the power of 15. In a solution in which copper has displaced some silver ions from the solution, concentration of Cu2+ ions is 1.8 x 10-2 mol L-1 and the concentration of Ag+ ions is 3·0 ×10–9 mol L–1. Is the system at equilibrium?

    Solution
    The given reaction in a state of equilibrium may be represented as:
    Cu left parenthesis straight s right parenthesis space plus space 2 Ag to the power of plus left parenthesis aq right parenthesis space space space rightwards harpoon over leftwards harpoon space space space Cu to the power of 2 plus end exponent left parenthesis aq right parenthesis space plus space 2 Ag left parenthesis straight s right parenthesis
    Applying the law of chemical equilibrium
                          straight K space equals space fraction numerator open square brackets Cu to the power of 2 plus end exponent left parenthesis aq right parenthesis close square brackets space open square brackets Ag left parenthesis straight s right parenthesis close square brackets squared over denominator open square brackets Cu left parenthesis straight s right parenthesis close square brackets space open square brackets Ag to the power of plus left parenthesis aq right parenthesis close square brackets squared end fraction
    By convention,   [Ag(s)] = 1 and (Cu(s)] = 1
    straight K space equals fraction numerator open square brackets Cu to the power of 2 plus end exponent left parenthesis aq right parenthesis close square brackets over denominator open square brackets Ag to the power of plus left parenthesis aq right parenthesis close square brackets squared end fraction
    Substituting, open square brackets Cu to the power of 2 plus end exponent left parenthesis aq right parenthesis close square brackets   
      equals space 1.8 space cross times space 10 to the power of negative 2 end exponent space mol space straight L to the power of negative 1 end exponent space and space open square brackets Ag to the power of plus left parenthesis aq right parenthesis close square brackets
equals space 3.0 space cross times space 10 to the power of negative 9 end exponent space mol space straight L to the power of negative 1 end exponent comma
    straight K space equals fraction numerator 1.8 space cross times space 10 to the power of negative 2 end exponent space mol space straight L to the power of negative 1 end exponent over denominator left parenthesis 3.0 space cross times space 10 to the power of negative 9 end exponent space mol space straight L to the power of negative 1 end exponent right parenthesis squared end fraction
space space space space equals space fraction numerator 1.8 space cross times space 10 to the power of negative 2 end exponent over denominator left parenthesis 3.0 space cross times space 10 to the power of negative 9 end exponent right parenthesis squared end fraction mol to the power of negative 1 end exponent straight L
space space space space equals space fraction numerator 1.8 over denominator 9.0 end fraction cross times 10 to the power of 16 space mol to the power of negative 1 end exponent straight L
space space space space equals space 2 cross times 10 to the power of 15 space mol to the power of negative 1 end exponent

    which is same as for the reaction in equilibrium.
    Hence the given system is in equilibrium.

    Question 122
    CBSEENCH11006421

    One mole of straight H subscript 2 straight O and one mole of CO are taken in a 10-litre vessel and heated to 725K. At equilibrium, 40% of water (by mass) reacts with carbon monoxide according to the equation

    straight H subscript 2 straight O left parenthesis straight g right parenthesis space plus space CO left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space space straight H subscript 2 left parenthesis straight g right parenthesis space plus space CO subscript 2 left parenthesis straight g right parenthesis.

    Calculate the equilibrium constant for the reaction. 

    Solution

    40% by mass of water = 40% by mole of water
    40% of one mole of water = fraction numerator 1 cross times 40 over denominator 100 end fraction equals 0.4 space mole
                  straight H subscript 2 straight O left parenthesis straight g right parenthesis space plus space CO left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space straight H subscript 2 left parenthesis straight g right parenthesis space plus space CO subscript 2 left parenthesis straight g right parenthesis
    Initial mole    1          1                 0           0
    Final mole   1-0.4       1-0.4           0.4         0.4
                   = 0.6         = 0.6
    According to the law of chemical equilibrium,
               
      straight K subscript straight c space equals space fraction numerator open square brackets straight H subscript 2 left parenthesis straight g right parenthesis close square brackets space open square brackets CO subscript 2 left parenthesis straight g right parenthesis close square brackets over denominator open square brackets straight H subscript 2 straight O left parenthesis straight g right parenthesis close square brackets space open square brackets CO left parenthesis straight g right parenthesis close square brackets end fraction
    Substituting the values, we have,
     
      straight K subscript straight c space equals space fraction numerator begin display style fraction numerator 0.4 over denominator 10 end fraction end style cross times begin display style fraction numerator 0.4 over denominator 10 end fraction end style over denominator begin display style fraction numerator 0.6 over denominator 10 end fraction end style cross times begin display style fraction numerator 0.6 over denominator 10 end fraction end style end fraction space equals space 0.44

    Question 123
    CBSEENCH11006422

    Reaction between N2 and O2 takes place as follows:
                   2 straight N subscript 2 left parenthesis straight g right parenthesis space plus space straight O subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space 2 straight N subscript 2 straight O left parenthesis straight g right parenthesis
    If a mixture of 0.482 mol of N2 and 0.933 mol of O2 is placed in a 10 L reaction vessel and allowed to form N2O at a temperature for which Kc = 2·0 × 10–37, determine the composition of equilibrium mixture.

    Solution
    The given reversible chemical reaction is
               2N2(g)     +    O2(g)       rightwards harpoon over leftwards harpoon     2N2O(g)
    Initial     0.482 mol      0.933 mol
    At equi.  4.482 - x        0.933 minus straight x over 2        x
    Molar conc. fraction numerator 0.482 minus straight x over denominator 10 end fraction space space fraction numerator 0.933 minus begin display style x over 2 end style over denominator 10 end fraction     straight x over 10
    As K = 2·0 × 10–37 is very small, this means that the amount of N2 and O2 reacted (x) is very very small. Hence, at equilibrium, we have
    open square brackets straight N subscript 2 close square brackets space equals space 0.482 space mol space straight L to the power of negative 1 end exponent
open square brackets straight O subscript 2 close square brackets space equals space 0.0933 space mol space straight L to the power of negative 1 end exponent
open square brackets straight N subscript 2 straight O close square brackets space equals space 0.1 space straight x
    According to the law of chemical equilibrium,
        straight K subscript straight c space equals space fraction numerator open square brackets straight N subscript 2 straight O left parenthesis straight g right parenthesis close square brackets squared over denominator open square brackets straight N subscript 2 left parenthesis straight g right parenthesis close square brackets squared space open square brackets straight O subscript 2 left parenthesis straight g right parenthesis close square brackets end fraction space... left parenthesis 1 right parenthesis
    Putting the values in expression (1), we have,
                 straight K subscript straight c space equals space fraction numerator left parenthesis 0.1 straight x right parenthesis squared over denominator left parenthesis 0.0482 right parenthesis squared left parenthesis 0.0933 right parenthesis end fraction
space space space space space space equals space 2.0 space cross times space 10 to the power of negative 37 end exponent space space space space space left square bracket Given right square bracket
    On solving straight x space equals space 6.6 space cross times 10 to the power of negative 20 end exponent
    open square brackets straight N subscript 2 straight O close square brackets space equals space 0.1 space straight x space equals space 0.1 space cross times space 6.6 space cross times space 10 to the power of negative 20 end exponent
space space space space space space space space space space equals space 6.6 space cross times space 10 to the power of negative 21 end exponent space mol space straight L to the power of negative 1 end exponent
    Question 124
    CBSEENCH11006423
    Question 125
    CBSEENCH11006424

    At 700K, equilibrium constant for the reaction:
       straight H subscript 2 left parenthesis straight g right parenthesis space plus space straight I subscript 2 left parenthesis straight g right parenthesis rightwards harpoon over leftwards harpoon space 2 HI left parenthesis straight g right parenthesis 
    is 54.8. If 0.5 mole/litre of HI(g) is present at equilibrium at 700K, what are the concentration of H2(g) and I2(g) assuming that we initially started with HI(g) and allowed it to reach equilibrium at 700 K?

    Solution
    Here, equilibrium constant for the reaction,
           straight H subscript 2 left parenthesis straight g right parenthesis space plus space straight I subscript 2 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space 2 HI left parenthesis straight g right parenthesis  
    is 54.8 . Thus the equilibrium constant for the reverse reaction
             2 HI left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space straight H subscript 2 left parenthesis straight g right parenthesis space plus space straight I subscript 2 left parenthesis straight g right parenthesis space would space be space fraction numerator 1 over denominator 54.8 end fraction
    Concentration of HI at equilibrium = 0.5 mole/litre[given]
    The concentration of H2 and I2 at equilibrium will be same.
    Suppose each of them = x mole /litre
    Applying law of chemical equilibrium to the above reaction,
               straight K subscript straight c space equals space fraction numerator open square brackets straight H subscript 2 left parenthesis straight g right parenthesis close square brackets space open square brackets straight I subscript 2 left parenthesis straight g right parenthesis close square brackets over denominator space open square brackets HI left parenthesis straight g right parenthesis close square brackets end fraction
    Substituting the values, we have,
            fraction numerator 1 over denominator 54.8 end fraction space equals space fraction numerator straight x space cross times space straight x over denominator left parenthesis 0.5 right parenthesis squared end fraction space equals space fraction numerator straight x squared over denominator 0.25 end fraction
    or space space space straight x squared space equals space fraction numerator 0.25 over denominator 54.8 end fraction space equals space 0.00456
or space space space space straight x space equals space 0.068 space mol space straight L to the power of negative 1 end exponent
    Question 126
    CBSEENCH11006425

    Ethyl acetate, is formed by the reaction of ethanol and acetic acid and equilibrium is represented as
    CH subscript 3 COOH left parenthesis straight l right parenthesis space plus space straight C subscript 2 straight H subscript 5 OH left parenthesis straight l right parenthesis space space rightwards harpoon over leftwards harpoon space space space CH subscript 3 COO subscript 2 straight H subscript 5 left parenthesis straight l right parenthesis space plus space straight H subscript 2 straight O left parenthesis straight l right parenthesis
    (i) Write the concentration ratio (reaction quotient), Qc, for this reaction (note:water is not in excess and is not a solvent in this reaction).
    (ii) At 293K, if one starts with 1·00 mol of acetic acid and 0·18 mol of ethanol, there is 0·171 mol of ethyl acetate in the final equilibrium mixture. Calculate the equilibrium constant.
    (iii) Starting with 0·5 mole of ethanol and 1·0 mole of acetic acid and maintaining it at 293K, 0·214 mole of ethyl acetate is formed after sometime. Has equilibrium been reached ?

    Solution
    (i) The various molar concentrations before the reaction and at equilibrium point may e represented as
           CH subscript 3 COOH left parenthesis straight l right parenthesis space plus space straight C subscript 2 straight H subscript 5 OH space left parenthesis straight l right parenthesis rightwards harpoon over leftwards harpoon space space CH subscript 2 COO subscript 2 straight H subscript 5 left parenthesis straight l right parenthesis space plus space straight H subscript 2 straight O left parenthesis straight l right parenthesis
    The concentration ratio Q for this reaction is given by,
    straight Q subscript straight C space equals space fraction numerator open square brackets CH subscript 3 COOC subscript 2 straight H subscript 5 left parenthesis straight l right parenthesis close square brackets space open square brackets straight H subscript 2 straight O left parenthesis straight l right parenthesis close square brackets over denominator open square brackets CH subscript 3 COOH left parenthesis straight l right parenthesis close square brackets space open square brackets straight C subscript 2 straight H subscript 5 OH left parenthesis straight l right parenthesis close square brackets end fraction

    (ii) The various molar concentrations before the chemical reaction and at equilibrium point may be represented as
                    CH subscript 3 COOH left parenthesis l right parenthesis space plus space straight C subscript 2 straight H subscript 5 OH left parenthesis l right parenthesis space space rightwards harpoon over leftwards harpoon space space CH subscript 3 COOC subscript 2 straight H subscript 5 left parenthesis l right parenthesis space plus space straight H subscript 2 straight O left parenthesis l right parenthesis
    Initialconc.          
    1 mole          0.180 ml         0                         0
    Equilibrium conc.          
    1 - 0.171    0.180 - 0.171  = 0.171         0.171 
     (0.829)         (0.009)      = 0.171         0.171
    Applying the law of chemical equilibrium,
           straight K subscript straight c space equals space fraction numerator open square brackets CH subscript 3 COOC subscript 2 straight H subscript 5 left parenthesis straight l right parenthesis close square brackets space open square brackets straight H subscript 2 straight O left parenthesis straight l right parenthesis close square brackets over denominator open square brackets CH subscript 3 COOH left parenthesis straight l right parenthesis close square brackets space open square brackets straight C subscript 2 straight H subscript 5 OH left parenthesis straight l right parenthesis close square brackets end fraction
space space space space equals space fraction numerator 0.171 space cross times space 0.171 over denominator 0.829 space cross times space 0.009 end fraction space equals 3.91
    (iii) The various molar concentrations before the reaction and at equilibrium point may be represented as
                           CH subscript 3 COOH left parenthesis straight l right parenthesis space plus space straight C subscript 2 straight H subscript 5 OH left parenthesis straight l right parenthesis space rightwards harpoon over leftwards harpoon space space space CH subscript 2 COO subscript 2 straight H subscript 5 left parenthesis straight l right parenthesis space plus space straight H subscript 2 straight O left parenthesis straight l right parenthesis
    Initial conc.        
    1.00 mole           0.5 mole     0                       0
    Equilibrium conc.         
    1 - 0.214        0.5- 0.214    =   0.214          0.214
                      
    (0.786)            (0.286)      =   0.214          0.214
    Concentration ratio,
                   straight Q subscript straight c space equals space fraction numerator open square brackets CH subscript 3 COOC subscript 2 straight H subscript 5 left parenthesis straight l right parenthesis close square brackets space open square brackets straight H subscript 2 straight O left parenthesis straight l right parenthesis close square brackets over denominator open square brackets CH subscript 3 COOH left parenthesis straight l right parenthesis close square brackets space open square brackets straight C subscript 2 straight H subscript 5 OH left parenthesis straight l right parenthesis close square brackets end fraction
equals space fraction numerator 0.214 space cross times space 0.214 over denominator 0.786 space cross times space 0.286 end fraction space equals space 0.204
    As the value of Qc is less than the value of equilibrium constant, therefore, the equilibrium has not reached.

    Question 127
    CBSEENCH11006426

    The ester, ethyl acetate is formed by the reaction of ethanol and acetic acid and equilibrium is represented as

    CH subscript 3 COOH left parenthesis straight l right parenthesis space plus space straight C subscript 2 straight H subscript 5 OH left parenthesis straight l right parenthesis space space rightwards harpoon over leftwards harpoon space space space CH subscript 3 COOC subscript 2 straight H subscript 5 left parenthesis straight l right parenthesis space plus space straight H subscript 2 straight O left parenthesis straight l right parenthesis

    We do not use dilute aqueous solution for this reaction. Why?

    Solution
    Since water is formed in the reaction, by taking dilute aqueous solution, the molar concentration of water will increase considerably. As a result, the equilibrium will shift in the backward direction. The above expression for equilibrium constant will no longer hold good because then [H2O] = 1.
    Question 128
    CBSEENCH11006427

    The ester, ethyl acetate, is formed by the reaction of ethanal and acetic acid and equilibrium is represented as

    CH subscript 3 COOH left parenthesis straight l right parenthesis space plus space straight C subscript 2 straight H subscript 5 OH left parenthesis straight l right parenthesis space rightwards harpoon over leftwards harpoon space space space CH subscript 3 COOC subscript 2 straight H subscript 5 left parenthesis straight l right parenthesis space plus space straight H subscript 2 straight O left parenthesis straight l right parenthesis

    (i) Why some concentrated sulphuric acid is usually added to the reaction mixture in a laboratory preparation of ethyl acetate?

    (ii) Since the heat of reaction is nearly zero for this reaction, how will the equilibrium constant depend on upon the temperature?

    Solution

    (i) Concentrated sulphuric acid is a dehydrating agent. It can absorb water. According to Le-Chatelier’s principle, the removal of water from the reaction mixture, equilibrium will shift in the forward direction producing more of ethyl acetate.
    (ii) Since the heat of reaction is nearly zero, the equilibrium constant is almost not affected by temperature.

    Question 129
    CBSEENCH11006428

    1 mole of acetic acid and 1 mole of ethyl alcohol were mixed at 298K. At equilibrium, 0 - 33 mole of acetic acid was found unreacted. Calculate the equilibrium constant for the reaction
                CH subscript 3 COOH plus straight C subscript 2 straight H subscript 5 OH space space rightwards harpoon over leftwards harpoon space space space CH subscript 3 COOC subscript 2 straight H subscript 5 space plus space straight H subscript 2 straight O
    Initial  conc.   
    1 mole      1 mole            1 mole       0 mole

    Equilibrium conc.
    0.333      0.333               0 mole        0 mole
                 

    Solution

    Since at equilibrium 0·33 mole of acetic acid is left, we say that 1 – 0·333 = 0·667 mole of acetic acid is used up.
    Now according to the equation, it is clear that 0·667 mole of acetic acid combines with a 0·667 mole of ethyl alcohol to form a 0·667 mole of ethyl acetate and a 0·667 mole of water.
    At equilibrium [CH3COOH] = 0·333 mole ; [C2H5OH] = 0·333 mole [CH3COOC2H5] = 0·667 mole;
    [H2O] = 0·667 mole
    Applying the law of chemical equilibrium, we have
    straight K subscript straight c space equals space fraction numerator open square brackets CH subscript 3 COOC subscript 2 straight H subscript 5 close square brackets space open square brackets straight H subscript 2 straight O close square brackets over denominator open square brackets CH subscript 3 COOH close square brackets space open square brackets straight C subscript 2 straight H subscript 5 OH close square brackets end fraction
        equals space fraction numerator 0.667 space cross times space 0.667 over denominator 0.333 space cross times space 0.333 end fraction space equals space 4

    Question 130
    CBSEENCH11006429

    What is the equilibrium concentration of each of the substances in the equilibrium when the initial concentration of ICl was 0·78 M?
    2 ICl left parenthesis straight g right parenthesis space rightwards harpoon over leftwards harpoon space space straight I subscript 2 left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis semicolon space space space straight K subscript straight c space equals 0.14

    Solution

    Let at equilibrium,
                                space open square brackets straight I subscript 2 close square brackets space equals space open square brackets Cl subscript 2 close square brackets space equals space straight x space mol space straight L to the power of negative 1 end exponent
    Then                      2 ICl space space rightwards harpoon over leftwards harpoon space space straight I subscript 2 left parenthesis straight g right parenthesis space plus space space Cl subscript 2 left parenthesis straight g right parenthesis
    Initial conc.            0.78 M       0            0
    At eqm.                 0.78 - 2x    x            x
    Applying the law of chemical equilibrium
                       straight K subscript straight c space equals fraction numerator open square brackets straight I subscript 2 left parenthesis straight g right parenthesis close square brackets space open square brackets Cl subscript 2 left parenthesis straight g right parenthesis close square brackets over denominator open square brackets ICl left parenthesis straight g right parenthesis close square brackets squared end fraction space space space space space... left parenthesis 1 right parenthesis
    Putting the values in expression (1), we have
            0.14 space equals space fraction numerator straight x space cross times space straight x over denominator left parenthesis 0.78 minus 2 straight x right parenthesis squared end fraction
            or space space space straight x squared space equals space 0.14 left parenthesis 0.78 minus 2 straight x right parenthesis squared
or space space space fraction numerator straight x over denominator 0.78 minus 2 straight x end fraction space equals square root of 0.14 end root space equals space 0.374
or space space space space space space straight x space equals space 0.292 space minus space 0.748 space straight x
or space space space space space 1.748 straight x space equals space 0.292
or space space space space space space space space straight x space equals space 0.167
    Hence, at equilibrium                  left square bracket straight I subscript 2 right square bracket space equals space open square brackets Cl subscript 2 close square brackets space equals space 0.167 space straight M
    and    
       
     open square brackets ICl close square brackets space equals space 0.78 space minus space 2 space cross times space 0.167 space straight M space equals space 0.446 space straight M

    Question 131
    CBSEENCH11006430

    Kp = 0·04 atm at 899 K for the equilibrium shown below. What is the equilibrium concentration of C2H6 when it is placed in a flask at 4·0 atm pressure and allowed to come to equilibrium?

                straight C subscript 2 straight H subscript 6 left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space straight C subscript 2 straight H subscript 4 left parenthesis straight g right parenthesis space plus space straight H subscript 2 left parenthesis straight g right parenthesis

    Solution

    Let at equilibrium,
                            straight p subscript straight c subscript 2 straight H subscript 4 end subscript space equals space straight p subscript straight H subscript 2 end subscript space equals space straight p
    The reaction is
                               straight C subscript 2 straight H subscript 6 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space straight C subscript 2 straight H subscript 4 left parenthesis straight g right parenthesis space plus space straight H subscript 2 left parenthesis straight g right parenthesis
    Initial pressure        4.0 atm           0              0
    At equm.                4 - p                p              p
    Applying the law of chemical equilibrium
                     
          straight K subscript straight p space equals space fraction numerator straight p subscript straight C subscript 2 straight H subscript 4 end subscript space cross times space straight p subscript straight H subscript 2 end subscript over denominator straight p subscript straight C subscript 2 straight H subscript 6 end subscript end fraction space space space space space... left parenthesis 1 right parenthesis
    Putting the reaction in expression (1),
    we have
        0.04 space equals space fraction numerator straight p squared over denominator 4 minus straight p end fraction
or space space space space space straight p squared space equals space 0.16 space minus space 0.04 space straight p
or space space space space space straight p squared plus 0.04 straight p space minus space 0.16 space equals space 0
therefore space space space space space straight p space equals space fraction numerator negative 0.04 space plus-or-minus space square root of 0.0016 minus 4 left parenthesis negative 0.16 right parenthesis end root over denominator 2 end fraction
space space space space space space space space space space space space space equals space fraction numerator negative 0.04 space plus-or-minus 0.89 over denominator 2 end fraction
    Taking positive value,
     straight p space equals fraction numerator 0.80 over denominator 2 end fraction space equals space 0.40
    therefore space space space space space space space space space space space space open square brackets straight C subscript 2 straight H subscript 6 close square brackets subscript eq space equals space 4 minus 0.40 space atm space equals space 3.60 space atm

    Question 132
    CBSEENCH11006431

    A sample of pure PCl5 was introduced into an evacuated vessel at 473K. After equilibrium was attained, the concentration of PCl5 was found to be 0·5 × 10–1 mol L–1. If the value of Kc is 8·3 × 10–3, what are the concentrations of PCl3 and Cl2 at equilibrium?
                      PCl subscript 5 left parenthesis straight g right parenthesis space rightwards harpoon over leftwards harpoon space space space PCl subscript 3 left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis

    Solution
    Let at equilibrium,
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#13 {main}</pre>
    PCl subscript 5 left parenthesis straight g right parenthesis space space space space space space space space space space space rightwards harpoon over leftwards harpoon space space space space space space space space space space space space space space space space space space space PCl subscript 3 left parenthesis straight g right parenthesis space space space plus space space space space Cl subscript 2 left parenthesis straight g right parenthesis
    At eq. 0.5 x 10-1 mol L-1      x mol L-1       x mol L-1
    Applying law of chemical equilibrium
           straight K subscript straight c space equals space fraction numerator open square brackets PCl subscript 3 left parenthesis straight g right parenthesis close square brackets space open square brackets Cl subscript 2 left parenthesis straight g right parenthesis close square brackets over denominator open square brackets PCl subscript 5 left parenthesis straight g right parenthesis close square brackets end fraction space space space space... left parenthesis 1 right parenthesis
    Putting the values in expression (1), we have
                       straight K subscript straight c space equals space fraction numerator straight x squared over denominator 0.5 space cross times space 10 to the power of negative 1 end exponent end fraction space equals space 8.3 space cross times space 10 to the power of negative 3 end exponent space space left square bracket Given right square bracket
straight x squared space equals space left parenthesis 8.3 space straight x space 10 to the power of negative 3 end exponent right parenthesis thin space left parenthesis 0.5 space cross times space 10 to the power of negative 1 end exponent right parenthesis
space space space space equals space 4.15 space cross times space 10 to the power of negative 4 end exponent
straight x space equals space square root of 4.15 space cross times space 10 to the power of negative 4 end exponent end root space equals space 2.04 space cross times space 10 to the power of negative 2 end exponent straight M
space space space equals space 0.02 space straight M
therefore space space open square brackets PCl subscript 3 close square brackets space equals space open square brackets Cl subscript 2 close square brackets space equals space 0.02 space straight M
    Question 133
    CBSEENCH11006432

    3·00 mol of PCl5 kept in 1L closed reaction vessel was allowed to attain equilibrium at 380K. Calculate the composition of the mixture at equilibrium, Kc = 1·80.

    Solution
    Let x mol of PCl5 be dissociated.
    The reaction is
                        PCl subscript 5 space space rightwards harpoon over leftwards harpoon space space space space space PCl subscript 3 space space plus Cl subscript 2
    Initial conc.      3.0           0           0
    At eqm.         3 - x           x           x
    Applying the law of chemical equilibrium
                     straight K subscript straight c space equals space fraction numerator open square brackets PCl subscript 3 close square brackets space open square brackets Cl subscript 2 close square brackets over denominator open square brackets PCl subscript 5 close square brackets end fraction                ...(1)
    Putting the values in expression (1), we have
                   1.8 space equals space fraction numerator straight x squared over denominator 3 minus straight x end fraction
    or space space straight x squared plus space 1.8 straight x space minus 5.4 space equals space 0
space space space space space space straight x space equals space fraction numerator open square brackets negative 1.8 space plus-or-minus square root of left parenthesis 1.8 right parenthesis squared minus 4 left parenthesis negative 5.4 right parenthesis end root close square brackets over denominator 2 end fraction
space space space space space straight x space equals space fraction numerator open square brackets negative 1.8 space plus-or-minus square root of 3.24 space plus-or-minus 21.6 end root close square brackets over denominator 2 end fraction
space space space space space straight x space equals space fraction numerator left square bracket 1.8 space plus-or-minus space 4.98 right square bracket over denominator 2 end fraction
space or space space straight x space equals space fraction numerator left square bracket negative 1.8 space plus 4.98 right square bracket over denominator 2 end fraction space equals 1.59
    therefore space space space open square brackets PCl subscript 5 close square brackets space equals space 3.0 space space minus space straight x space equals space 3.0 space minus space 1.59 space equals space 1.41 space straight M
space space space space space space open square brackets PCl subscript 3 close square brackets space equals space open square brackets Cl subscript 2 close square brackets space equals space straight x space equals space 1.59 space straight M

    Question 134
    CBSEENCH11006433

    Bromine monochloride (BrCl) decomposes into bromine and chlorine and attains the equilibrium:
    space 2 BrCl space rightwards harpoon over leftwards harpoon space space space space Br subscript 2 left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis
    for which Kc = 32 at 500 K. If initially pure BrCl is present at a concentration of 3·30×10–3 mol L–1 what is its molar concentration in the mixture at equilibrium?

    Solution
    The reaction is
                          space space space space space space space space space space space space space space space space space space space space space 2 BrCl left parenthesis straight g right parenthesis space space space space space space space space space space rightwards harpoon over leftwards harpoon space space space space space space space space space space Br subscript 2 left parenthesis straight g right parenthesis space plus space Cl subscript 2 left parenthesis straight g right parenthesis
    Initial moles/litre          
                3.30 x 10-3 mol-1      0              0
    At equilibrium
               (3.30 x 10-3 -x)        x/2           x/2

    where x moles of BrCl decompose in order to attain equilibrium.
    Applying the law of chemical equilibrium
           straight K subscript straight c space equals space fraction numerator open square brackets Br subscript 2 close square brackets space open square brackets Cl subscript 2 close square brackets over denominator open square brackets BrCl close square brackets squared end fraction space space space space space... left parenthesis 1 right parenthesis

    Putting the values in expression (1), we have
          space straight K subscript straight c space equals space fraction numerator open parentheses begin display style straight x over 2 end style close parentheses space open parentheses begin display style straight x over 2 end style close parentheses over denominator left parenthesis 3.30 space cross times space 10 to the power of negative 3 end exponent space minus straight x right parenthesis squared end fraction space equals space 32 space left square bracket Given right square bracket
space therefore space space space space space space space fraction numerator straight x squared over denominator 4 left parenthesis 3.30 space cross times space 10 to the power of negative 3 end exponent minus straight x right parenthesis end fraction space equals space 32
    On taking the square root, we have,
         fraction numerator straight x over denominator 2 left parenthesis 3.30 space cross times space 10 to the power of negative 3 end exponent minus straight x right parenthesis end fraction space equals space square root of 32 space equals space 5.66
                                    space straight x space equals 11.32 space left parenthesis 3.30 space cross times space 10 to the power of negative 3 end exponent minus straight x right parenthesis
    space or space space space space space space 12.32 straight x space equals space 11.32 space cross times space 3.30 space cross times space 10 to the power of negative 3 end exponent
or space space space space space space space space space space space straight x space equals space 3.0 space cross times space 10 to the power of negative 3 end exponent
    therefore   At equilibrium
    space open square brackets BrCl close square brackets space equals space left parenthesis 3.30 space cross times space 10 to the power of negative 3 end exponent space minus 3.0 space cross times space 10 to the power of negative 3 end exponent right parenthesis
space space space space space space space space space equals space 0.30 space cross times space 10 to the power of negative 3 end exponent
space space space space space space space space space space equals 3.0 space cross times space 10 to the power of negative 4 end exponent mol space straight L to the power of negative 1 end exponent
    Question 135
    CBSEENCH11006434

    The value of Kc = 4·24 at 800 K for the reaction:
    CO left parenthesis straight g right parenthesis space plus space straight H subscript 2 straight O left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space CO subscript 2 left parenthesis straight g right parenthesis space plus space straight H subscript 2 left parenthesis straight g right parenthesis
    Calculate equilibrium concentration of CO2, H2, CO and H2O at 800K, if only CO and H2O are present initially at concentrations of 0·10M each. 

    Solution
    The reaction is
                 space space space space space space space space space space space space space space space space CO left parenthesis straight g right parenthesis space plus space straight H subscript 2 straight O left parenthesis straight g right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space CO subscript 2 left parenthesis straight g right parenthesis space plus space straight H subscript 2 left parenthesis straight g right parenthesis
    Initial conc          0.1 M          0.1 M             0              0
    At eqm.          (0.1 - x)M       (0.1 -x)M         xM           xM
    where x mole of each of the product be formed.
     Applying law of chemical equilibrium, we have
                     straight K subscript straight c space equals space fraction numerator open square brackets CO subscript 2 left parenthesis straight g right parenthesis close square brackets space open square brackets straight H subscript 2 left parenthesis straight g right parenthesis close square brackets over denominator open square brackets CO left parenthesis straight g right parenthesis close square brackets space open square brackets straight H subscript 2 straight O left parenthesis straight g right parenthesis close square brackets end fraction space space space space space... left parenthesis 1 right parenthesis
    Putting the values in expression (1), we have
                        4.24 space equals space fraction numerator straight x squared over denominator left parenthesis 0.1 minus straight x right parenthesis squared end fraction space equals space fraction numerator straight x over denominator 0.1 space minus straight x end fraction space equals space 2.06
      or space space space space space space space straight x space equals space 2.06 space left parenthesis 0.1 minus straight x right parenthesis
or space space space space space space space straight x space equals space 0.206 minus 2.06 space straight x
or space space space space 3.06 space straight x space equals space 0.206
or space space space space space space space space straight x space equals space fraction numerator 0.206 over denominator 3.06 end fraction space equals space 0.067

    therefore space space space space open square brackets CO subscript 2 close square brackets subscript eq space equals space open square brackets straight H subscript 2 close square brackets subscript eq space equals space 0.067 space straight M
or space space space space open square brackets CO close square brackets subscript eq space equals space open square brackets straight H subscript 2 straight O close square brackets subscript eq space equals space 0.1 minus 0.067
space space space space equals space 0.033 space straight M
     
     

    Question 136
    CBSEENCH11006435

    Dihydrogen gas used in Haber’s process is produced by reacting methane from natural gas with high temperature steam. The first stage of two stage reaction involves the formation of CO and H2. In second stage, CO formed in first stage is reacted with more steam in water gas shift reaction,
    CO left parenthesis straight g right parenthesis space plus space straight H subscript 2 straight O left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space space space CO subscript 2 left parenthesis straight g right parenthesis space plus space straight H subscript 2 left parenthesis straight g right parenthesis
    If a reaction vessel at 400°C is charged with an equimolar mixture of CO and steam such that pCO = 4·0 bar, what will be the partial pressure of H2 at equilibrium ? Kp = 10·1 at 400°C. 


     

    Solution

    Suppose the partial pressure of H2 at equilibrium  = p bar
                             CO left parenthesis straight g right parenthesis space plus space straight H subscript 2 straight O space space space rightwards harpoon over leftwards harpoon space space space space space CO subscript 2 left parenthesis straight g right parenthesis space plus space straight H subscript 2 left parenthesis straight g right parenthesis
    Initial pressure      4.0 bar   4.0bar =   -            -
    At eqm.          
                             (4 -p)     (4-p) =      p            p
    Applying the law of chemical equilibrium,
         straight K subscript straight p space equals space fraction numerator straight p subscript CO subscript 2 end subscript space cross times space straight p subscript straight H subscript 2 end subscript over denominator straight p subscript CO cross times space straight p subscript straight H subscript 2 straight O end subscript end fraction space space space space... left parenthesis 1 right parenthesis    
    Putting the values in expression (1), we have
       straight K subscript straight p space equals space fraction numerator straight p space cross times space straight p over denominator left parenthesis 4 minus straight p right parenthesis thin space left parenthesis 4 minus straight p right parenthesis end fraction
space space space space space equals space fraction numerator straight p squared over denominator left parenthesis 4 minus straight p right parenthesis squared end fraction space equals space 0.1 space space space space space space space left square bracket given right square bracket
therefore space space space space fraction numerator 4 over denominator 4 minus straight p end fraction space equals space square root of 0.1 end root space equals space 0.316
therefore space space space space space straight p space equals space 1.264 space minus space 0.316 straight p
space or space space space 1.316 straight p space equals space 1.264 space or space space straight p space equals space 0.96 space bar           
                                 

    Question 137
    CBSEENCH11006436

    The value of increment straight G degree for the phoshorylation of glucose in glycolysis is 13.8 kJ/mol. Find the value of Kc at 298 K.

    Solution
    space increment straight G degree space equals space minus RT space ln space straight K subscript straight c space equals space minus 2.303 space RT space log space straight K subscript straight c               ...(1)
     Here comma space increment straight G degree space equals 13.8 space kJ space mol to the power of negative 1 end exponent space equals space 13.8 space cross times space 10 cubed straight J space mol to the power of negative 1 end exponent
space space space space space space space space space space straight R space equals space 8.314 space JK to the power of negative 1 end exponent mol to the power of negative 1 end exponent
space space space space space space space space space space straight T space equals space 298 space straight K space

       Putting the values in expression (1), we have

    13.8 space cross times space 10 cubed straight J space mol to the power of negative 1 end exponent space equals space 2.303 space cross times space left parenthesis 8.314 space JK to the power of negative 1 end exponent space mol to the power of negative 1 end exponent right parenthesis space cross times space left parenthesis 298 straight K right parenthesis space log space straight K subscript straight c
     On solving,
    straight K subscript straight c space equals space 3.81 space cross times space 10 to the power of negative 3 end exponent
    Question 138
    CBSEENCH11006437

    Hydrolysis of sucrose gives,
    Sucrose space plus space straight H subscript 2 straight O space rightwards harpoon over leftwards harpoon space space Glucose space plus space Fructose
    Equilibrium constant Kc for the reaction is 2 cross times 10 to the power of 13 space at space 300 space straight K. Calculate increment straight G degree at 300K.

    Solution

    We know,
           increment straight G degree space equals space minus RT space ln space straight K subscript straight c space equals space minus 2.303 space straight R space straight T space log space straight K subscript straight c space space space... left parenthesis 1 right parenthesis
     Here comma space space space space space straight K subscript straight c space equals space 2 space cross times space 10 to the power of 13
space space space space space space space space space space space space straight T space equals 300 space straight K comma
space space space space space space space space space space space space straight R space equals space 8.314 space JK to the power of negative 1 end exponent space mol to the power of negative 1 end exponent
    Putting the values in expression (1), we have
           increment straight G degree equals space minus 2.303 space cross times space left parenthesis 8.314 space JK to the power of negative 1 end exponent space mol to the power of negative 1 end exponent right parenthesis space left parenthesis 300 space straight K right parenthesis space log space left parenthesis 2 cross times 10 to the power of negative 13 end exponent right parenthesis
or space space space increment straight G to the power of 0 space equals space minus 7.64 space cross times space 10 to the power of 4 space straight J space mol to the power of negative 1 end exponent

    Question 139
    CBSEENCH11006438

    Calculate: (a) ∆G° and (b) the equilibrium constant for the formation of NO2from NO and O2 at 298 K.
         NO left parenthesis straight g right parenthesis space plus space 1 half straight O subscript 2 left parenthesis straight g right parenthesis space space space leftwards harpoon over rightwards harpoon space space space NO subscript 2 left parenthesis straight g right parenthesis
    where increment subscript straight f straight G to the power of 0 space left parenthesis NO subscript 2 right parenthesis space equals space 52.0 space kJ divided by mol comma space space increment subscript straight f straight G to the power of 0 left parenthesis NO right parenthesis space equals space 87.0 space kJ divided by mol comma space increment subscript straight f straight G to the power of 0 left parenthesis straight O subscript 2 right parenthesis space equals space 0 space kJ divided by mol.        
         

    Solution

    (a) We know, 
                increment subscript straight r straight G to the power of 0 space equals space sum from blank to blank of increment subscript straight f straight G to the power of 0 space left parenthesis Products right parenthesis space minus space sum from blank to blank of increment subscript straight f straight G to the power of 0 left parenthesis Reactants right parenthesis
             equals space increment subscript straight f straight G to the power of 0 left parenthesis NO subscript 2 right parenthesis space minus space open square brackets increment subscript straight f straight G to the power of 0 left parenthesis NO right parenthesis space plus space 1 half increment subscript straight f straight G to the power of 0 left parenthesis straight O subscript 2 right parenthesis close square brackets
space equals space 52.0 space minus space open parentheses 87.0 space plus space 1 half cross times 0 close parentheses space equals space minus 35.0 space kJ space mol to the power of negative 1 end exponent
    space left parenthesis straight b right parenthesis space space We space know comma space
space space increment straight G to the power of 0 space equals space minus 2.303 space RT space log space straight K
space minus 35000 space straight J space mol to the power of negative 1 end exponent space equals space minus 2.303 space cross times space left parenthesis 8.314 space JK to the power of negative 1 end exponent space mol to the power of negative 1 end exponent right parenthesis space cross times space left parenthesis 298 straight K right parenthesis space cross times space log space straight K
or space space space log space straight K space equals space 6.1341
or space space space space straight K space equals space antilog space left parenthesis 6.1341 right parenthesis space equals space 1.361 space cross times space 10 to the power of 6
                  
               

    Question 144
    CBSEENCH11006443

    At 1127 K and 1 atm pressure, a gaseous mixture of CO and CO2 in equilibrium with solid carbon has 90.55% CO by mass
                           straight C left parenthesis straight s right parenthesis space plus space CO subscript 2 left parenthesis straight g right parenthesis space space rightwards harpoon over leftwards harpoon space 2 CO left parenthesis straight g right parenthesis
    Calculate Kfor this reaction at the above example. 

    Solution

    If the total mass of the mixture of CO and CO2 is 100g. then the mass of CO=90.55g and mass of 
    CO2= 100-90.55=9-45g
    therefore,
    Number of moles of CO= 90.55/28=3.23
    Number of moles of CO= 9.45/44 =0.22
    therefore comma
space straight p subscript CO space equals fraction numerator 3.23 over denominator 3.23 space plus 0.22 end fraction space straight x space 1 space atm space equals space 0.94 space atm

straight p subscript CO subscript 2 end subscript space equals space fraction numerator 0.22 over denominator 3.23 plus 0.22 end fraction space straight x space 1 space atm space equals 0.06 space atm

straight K subscript straight p space equals space straight p squared subscript CO subscript 2 end subscript over straight p subscript CO space equals space fraction numerator left parenthesis 0.94 right parenthesis squared over denominator 0.06 space end fraction space equals 14.25
increment straight n subscript straight g space equals 2 minus 1 space equals 1
straight K subscript straight p space equals straight K subscript straight c left parenthesis RT right parenthesis
straight K subscript straight c space equals space straight K subscript straight p over RT space equals fraction numerator 14.25 over denominator 0.08210 space straight x 1127 end fraction space equals 0.154

    Question 145
    CBSEENCH11006444

    What is the process of neutralisation according to Bronsted-Lowry concept?

    Solution

    Neutralisation is the process of formation of a conjugate base and a conjugate acid of the original acid and base which react respectively. For example,
    HCl space plus space NH subscript 3 space space rightwards harpoon over leftwards harpoon space space space NH subscript 4 superscript plus space plus space Cl to the power of minus
     Cl to the power of minus is the conjugate base of HCl and NH subscript 4 superscript plus is the conjugate acid of NH3.

    Question 146
    CBSEENCH11006445

    What is the conjugate base?

    Solution
    The residual part of an acid after the removal of the proton is called the conjugate base of that acid.
    Acid space space rightwards arrow space space space straight H to the power of plus space plus space Conjugate space base
HCl space space rightwards arrow space space space straight H to the power of plus plus Cl to the power of minus
    Cl to the power of minus is the conjugate base of HCl.
    Question 147
    CBSEENCH11006446

    What is conjugate acid?

    Solution
    The substance resulting after the addition of a proton to a base is called conjugate acid of that base.
    Base plus straight H to the power of plus space space rightwards arrow space space space Conjugate space acid
NH subscript 3 plus straight H to the power of plus space space space rightwards arrow space NH subscript 4 superscript plus
    NH subscript 4 superscript plus  is the conjugate acid of NH3.
    Question 148
    CBSEENCH11006447

    What are conjugate pairs?

    Solution
    The acid and its conjugate base are called a conjugate pair. Similarly, the base and its conjugate acid are called a conjugate pair.
    Acid + Conjugate base : Conjugate pair
    Base + Conjugate acid : Conjugate pair
    Question 149
    CBSEENCH11006448

    What are amphiprotic or amphoteric substances?

    Solution
    Substances which can act both as acids, as well as bases, are called amphiprotic or amphoteric substances.
    Question 150
    CBSEENCH11006449

    With suitable examples, show that water acts as Bronsted acid as well as Bronsted base.

    Solution
    H2O as Bronsted acid:
                       NH subscript 3 plus space straight H subscript 2 straight O space space rightwards harpoon over leftwards harpoon space space space NH subscript 4 superscript plus space plus space OH to the power of minus
    straight H subscript 2 straight O as a Bronsted base:
                               HCl space plus space straight H subscript 2 straight O space space rightwards harpoon over leftwards harpoon space space space space space straight H subscript 3 straight O to the power of plus space plus space Cl to the power of minus
    Question 151
    CBSEENCH11006450

    What is the conjugate acid of CH3COO ?

    Solution
    CH3COOH (acetic acid).
    Question 152
    CBSEENCH11006451

    What is the conjugate base of HSO subscript 4 superscript minus ?

    Solution
    SO subscript 4 superscript 2 minus end superscript(Sulphate ion) is the conjugate base.
    Question 153
    CBSEENCH11006452

    What is the conjugate base of HCO subscript 3 superscript 2 minus end superscript?

    Solution
    CO subscript 3 superscript 2 minus end superscript is the conjugate base.
    Question 154
    CBSEENCH11006453

    Select conjugate acid base pair from the following equations:

    left parenthesis straight i right parenthesis space HF plus HNO subscript 3 space rightwards harpoon over leftwards harpoon space space space straight H subscript 2 NO subscript 3 superscript plus space plus space straight F to the power of minus
left parenthesis ii right parenthesis space HNO subscript 3 plus space straight H subscript 2 straight O space rightwards harpoon over leftwards harpoon space space straight H subscript 3 straight O to the power of plus space plus space NO subscript 3 superscript minus

    Solution
    left parenthesis straight i right parenthesis space HF vertical line straight F to the power of minus space and space straight H subscript 2 NO subscript 3 superscript plus vertical line HNO subscript 3 are conjugate acid base pair.
    left parenthesis ii right parenthesis space HNO subscript 3 vertical line NO subscript 3 superscript minus space and space straight H subscript 3 straight O to the power of plus space plus space vertical line straight H subscript 2 straight O space are conjugate acid base pair.
    Question 155
    CBSEENCH11006454

    What is neutralisation according to Bronsted Lowry concept?

    Solution
    It is the transfer of proton from acid to base.
    Question 156
    CBSEENCH11006455

    Classify acids and bases:
    SO subscript 4 superscript 2 minus end superscript semicolon space NH subscript 4 superscript plus semicolon space CH subscript 3 COO to the power of minus.

    Solution
    Acid colon space NH subscript 4 superscript plus semicolon space
Bases colon space SO subscript 4 superscript 2 minus end superscript comma space space CH subscript 3 COO to the power of minus.
    Question 157
    CBSEENCH11006456

    What are aprotic acids ?

    Solution
    Acids without any protons are called aprotic acids, in other world  Acids which neither accept nor donate hydrogen ions.e.g. AlCl3, FeCl3, BF3 etc.
    Question 158
    CBSEENCH11006457

    Which of the following are Lewis acids and which are Lewis bases:
    NH3, AlCl3, Ag+,OH

    Solution

    Lewis bases : NH3, OH ;
    Lewis acids : AlCl3, Ag+

    Question 159
    CBSEENCH11006458

    Which of the following are Lewis acids : H2O, BF3, H+ and NH4+?

    Solution
    BF3,NH4+ and H+, because these are electron deficient and accept lone pair of elections.
    Question 160
    CBSEENCH11006459

    What is neutralisation according to Lewis concept?

    Solution

    A Lewis base is a substance that can donate a pair of electrons to form a new bond.Neutralisation is the sharing of an electron pair between an acid and base.

    Question 161
    CBSEENCH11006460

    How is ionic product of water affected if an acid or base is added to water at the same temperature?

    Solution
    It remains uneffected i.e. it is constant at constant temperature.
    Question 162
    CBSEENCH11006461

    Which factor determines the strength of an acid?

    Solution
    Rate of ionisation of acid determines the strength of an acid.
    Question 163
    CBSEENCH11006462

    Select strong electrolytes, weak electrolytes and non-electrolytes cut of HCl, NH4OH, urea, KOH, NaCl, sugar, CH3COOH.

    Solution
    Strong electrolytes : HCl, KOH, NaCl Weak electrolytes: NH4OH, CH3COOH
    Non-electrolytes: Sugar urea.
    Question 164
    CBSEENCH11006463

    How does degree of dissociation of a weak acid (HA) vary with concentration?
    Or
    What is Ostwald’s dilution law?

    Solution
    straight alpha space equals space square root of straight K subscript straight a over straight C end root space where space straight K subscript straight a space is space the space ionisation. space
    constant of acid, C is the molar concentration and a is the degree of dissociation at concentration C.
    Question 165
    CBSEENCH11006464

    What is pH of a solution?

    Solution

    The pH of a solution is a measure of the molar concentration of hydrogen ions in the solution and as such is a measure of the acidity or basicity of the solution.

    pH = – log [H3O+].
    Question 166
    CBSEENCH11006465

    What is pH scale?

    Solution

    Hydronium ion concentration in molarity is more conveniently expressed on a logarithmic scale known as the pH scale.

    Question 167
    CBSEENCH11006466

    What is the range of pH value of:
    (i) acids    (ii) bases?

    Solution

    Acids: pH ranges 1 to 7.
    Bases: pH ranges 7 to 14.

    Question 168
    CBSEENCH11006467
    Question 170
    CBSEENCH11006469

    Acetic acid is highly soluble in water but is ionised to a small extent. Is it a strong or weak electrolyte ?

    Solution
    It is a weak electrolyte because the strength of the electrolyte is not related to the solubility of the salt in water, but to its ionisation.
    Question 171
    CBSEENCH11006470

    Who introduced pH scale?

     

    Solution

    S.P. Sorensen in 1909. 

    Question 172
    CBSEENCH11006471

    Which is a Lewis base:
    BCl subscript 3 space plus space PH subscript 3 space rightwards arrow space space space Cl subscript 3 straight B colon space space PH subscript 3

    Solution
    PH3.
    Question 173
    CBSEENCH11006472

    What happens to the pH if a few drops of acid are added to CH3 COONH4 solution ?

    Solution
    pH will remain almost constant because CH3COONH4 solution is a buffer.
    Question 174
    CBSEENCH11006473

    What type of acid is proton?

    Solution
    Lewis acid.
    Question 175
    CBSEENCH11006474

    What is the nature of aqueous KCl solution?

    Solution
    Neutral, pH = 7.
    Question 176
    CBSEENCH11006475
    Question 177
    CBSEENCH11006476

    Why is Al3+ Lewis acid?

    Solution
    Al3+ has an empty orbital. It can accept a pair of electrons.
    Question 178
    CBSEENCH11006477

    Give the conjugate acid - base pairs in dilute sulphuric acid.

    Solution
    H2SO4 and HSO4 ; H3O+ and OH.
    Question 179
    CBSEENCH11006478
    Question 180
    CBSEENCH11006479

    Out of CH3COO and OH which is stronger base and why?

    Solution
    OH ion can combine with H+ ions more readily than CH3COO ions. Hence OHis a stronger base.
    Question 181
    CBSEENCH11006480

    What is the difference between solubility product and ionic product?

    Solution
    Both are the products of the concentration of ions; solubility product is for a saturated solution whereas ionic product can be for any solution – saturated or unsaturated.
    Question 183
    CBSEENCH11006482

    What is the relationship between pH and pOH?

    Solution
    pH + pOH = pKw = 14.
    Question 184
    CBSEENCH11006483

    What is the maximum value of the ionic product of a salt at a particular temperature ?

    Solution

    The maximum value of the ionic product is equal to the solubility product constant, Ksp.

    Question 185
    CBSEENCH11006484

    How does the degree of ionisation of a weak acid change with the increase in concentration ?

    Solution
    It decreases with the increase in concentration.
    Question 186
    CBSEENCH11006485

    Under what condition a precipitate is formed if two solutions are mixed ?

    Solution
    When an ionic product is greater than the solubility product, then a precipitate is formed.
    Question 187
    CBSEENCH11006486

    What is common ion effect?

    Solution

    The phenomenon of suppression of the degree of dissociation of a weak acid or a weak base by the addition of a strong electrolyte containing a common ion is known as common ion effect. 

    Question 188
    CBSEENCH11006487

    How does the ionisation of H2S change in the presence of HCl?

    Solution

    Due to common-ion effect (H+ ions), ionisation of H2S is suppressed.

    Question 189
    CBSEENCH11006488

    During qualitative analysis, why NH4Cl and NH4OH are added in the III group?

    Solution
    Due to common ion effect (NH4+ ions), NH4Cl reduces the ionisation of NH4OH. Then hydroxides of III group only (but not of those of IV group) are precipitated.
    Question 191
    CBSEENCH11006490

    What are electrolytes and non-electrolytes?

    Solution

    Generally,the substances which can conduct electric current by the migration of ions through their molten states or aqueous solutions.
    Acids: HCl, HNO3, H2SO4, CH3COOH etc.
    Bases: NaOH, KOH, NH4OH, Ca(OH)2 etc.
    Salts: NaCl, NH4Cl, CH3COONH4, CaCletc.
    Non-electrolytes: The substances which do not conduct electric current through their molten states or aqueous solutions are known as non-electrolytes. For example, glucose, fructose, cane sugar, glycerol.

    Question 192
    CBSEENCH11006491

    Discuss different types of electrolytes.

    Solution
    Depending upon the degree of ionisation, there are two types of electrolytes.
    (i) Strong electrolyte: A substance which dissociates almost completely into ions in its aqueous solution is known as strong electrolyte". Even though the amount of strong electrolyte may be small, the concentration of ions in aqueous solution is high and thus electrical conductivity is also high e.g. HCl, HNO3, H2SO4, NaOH, KOH, NaCl, NaNO3. There is no equilibrium in their aqueous solutions since only a few molecules may be unionised. Their ionised form may be rep- resented as,
    HCl space plus space straight H subscript 2 straight O space space rightwards arrow space space straight H subscript 3 straight O to the power of plus space space plus space Cl to the power of minus
HNO subscript 3 plus straight H subscript 2 straight O space space space rightwards arrow space space space straight H subscript 3 straight O to the power of plus space plus space NO subscript 3 superscript minus
    (ii) Weak electrolyte: A substance which dissociates to a small extent in its aqueous solution is known as a weak electrolyte. Even though the amount of weak electrolyte may be large, the concentration of ions in solution is low and thus electrical conductivity is-low, for example, HF, H2CO3, H2C2O4, H3PO4, CH3COOH, HCN. Since weak electrolytes are feebly ionised in their aqueous solution, an equilibrium is set up between the ion3 and unionised electrolyte. For example.
                   CH subscript 3 COOH space plus space aq space space rightwards harpoon over leftwards harpoon space space space CH subscript 3 COO to the power of minus left parenthesis aq right parenthesis space plus space straight H to the power of plus left parenthesis aq right parenthesis
space space HCN space plus space aq space rightwards harpoon over leftwards harpoon space space space straight H to the power of plus left parenthesis aq right parenthesis space plus space CN to the power of minus left parenthesis aq right parenthesis
    Question 193
    CBSEENCH11006492

    What is a degree of ionisation ?

    Solution
    Some substances when dissolved in water form positive and negative ions. The breaking of the substances into ions, when dissolved in a solvent, is called ionisation. The extent to which an electrolyte undergoes ionisation is expressed in terms of degree of ionisation and it may be defined as the fraction of electrolyte which dissociates into ions.
    Mathematically,

    Degree space of space Ionisation comma
space space left parenthesis straight alpha right parenthesis space equals space fraction numerator Molarity space of space cation space or space anion space over denominator Original space molarity space of space electrolyte end fraction
    Clearly, the degree of ionisation is taken per mole of an electrolyte. For example, if 0·5 mole weak acid HA ionises to give 0·02 mole H+ (aq) or 0·02 mole A (aq), the degree of ionisation per mole of the electrolyte.HA would be
    HA space stack rightwards harpoon over leftwards harpoon space with Water on top space straight H to the power of plus left parenthesis aq right parenthesis space plus space straight A to the power of minus subscript left parenthesis aq right parenthesis end subscript
straight alpha space equals space fraction numerator 0.02 over denominator 0.5 end fraction space equals space 1 over 25
therefore space space space space Percent space ionisation space equals space 100 over 25 space equals space 4
    Question 194
    CBSEENCH11006493

    Discuss the ionisation of weak electrolytes (Ostwald’s dilution law).

    Solution
    As the weak electrolytes are ionised to a small extent, there is a state of equilibrium between the unionised electrolyte and the ions formed in solution. To illustrate.this, let us consider a weak electrolyte HA to be dissolved in water, a be the degree of ionisation and C be the molar concentration of HA.
                                      HA rightwards harpoon over leftwards harpoon    H+(aq) + A-(aq)
    Initial  conc.                C            0               0
    Equilibrium conc.     straight C minus Cα      Cα              Cα
    Applying law of chemical equilibrium,
                     straight K subscript straight a space equals space fraction numerator open square brackets straight H to the power of plus left parenthesis aq right parenthesis close square brackets space space open square brackets straight A to the power of minus left parenthesis aq right parenthesis close square brackets over denominator open square brackets HA left parenthesis aq right parenthesis close square brackets end fraction
    where Ka is ionisation (or dissociation) constant of the weak acid HA.
    or space space space space space straight K subscript straight a space equals space fraction numerator Cα space cross times space Cα over denominator straight C minus Cα end fraction space equals space fraction numerator straight C squared straight alpha squared over denominator straight C left parenthesis 1 minus straight alpha right parenthesis end fraction space equals space fraction numerator Cα squared over denominator 1 minus straight alpha end fraction
    This equation is often referred to as Ostwald’ dilution law equation since the degree of dissociation of a weak electrolyte is very small as compared to unity.
    therefore space space space space left parenthesis 1 minus straight alpha right parenthesis space can space be space taken space as space one space open square brackets because space straight a less than less than 1 close square brackets
or space space space space straight K subscript straight a space equals space Cα squared
or space space space space space straight alpha squared space equals space straight K subscript straight a over straight C
therefore space space space space straight alpha space equals space square root of straight K subscript straight a over straight C end root space space or space space straight alpha space proportional to space square root of 1 over straight C end root
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space space straight K subscript straight a space is space constant close square brackets

    Thus, the degree of ionisation of a weak electrolyte is inversely proportional to the square root of the molar concentration of the solution of the electrolyte.
    Hence the degree of ionisation of weak electrolyte goes on increasing with the decrease in molar concentration i.e. with dilution and it reaches the maximum value (unity) in very dilute solution. Thus, all weak electrolytes undergo almost complete ionisation at infinite dilution.
    For a weak base BOH:
    Let us consider a weak base BOH dissolved in water, a be the degree of ionisation and C be the molar concentration of BOH.
                             BOH space space space rightwards harpoon over leftwards harpoon space space space space straight B to the power of plus left parenthesis aq right parenthesis space space space plus space space space space OH to the power of minus left parenthesis aq right parenthesis
    Initial conc.           C              0                 0
    Equilibrium        straight C minus Cα         Cα                 Cα
    conc. 
    Applying law of chemical equilibrium,
    straight K subscript straight b space equals space fraction numerator open square brackets straight B to the power of plus left parenthesis aq right parenthesis close square brackets space open square brackets OH to the power of minus left parenthesis aq right parenthesis close square brackets over denominator open square brackets BOH space left parenthesis aq right parenthesis close square brackets end fraction space equals space fraction numerator Cα space cross times space Cα over denominator straight C space minus space Cα end fraction
space space space space space space equals space fraction numerator straight C squared straight alpha squared over denominator straight C left parenthesis 1 minus straight alpha right parenthesis end fraction space equals space fraction numerator Cα squared over denominator 1 minus straight alpha end fraction
straight K subscript straight b space equals space Cα squared space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space space straight a less than less than less than 1 close square brackets
or space space space straight alpha squared space equals space straight K subscript straight b over straight C
or space space space space straight alpha space equals space square root of straight K subscript straight b over straight C end root

    Question 197
    CBSEENCH11006496

    Calculate the degree of ionisation and hydronium ion concentration of a 0·02 M acetic acid at 298K. The dissociation constant of acid is 1·8 × 10–5 at 298K.

    Solution
    Let a be the degree of dissociation of the acetic acid.
    CH3COOH     rightwards harpoon over leftwards harpoon with Water on top    CH3COO-(aq) + H3O+
    Initial conc.
           C                     0                   0
    Equilibrium
     straight C minus Cα                    Cα                Cα
    Applying law of chemical equilibrium,
       
     straight K subscript straight a space equals space fraction numerator open square brackets CH subscript 3 COO to the power of minus left parenthesis aq right parenthesis close square brackets space open square brackets straight H subscript 3 straight O to the power of plus close square brackets over denominator open square brackets CH subscript 3 COOH close square brackets end fraction
or space space space space space space space space space straight K subscript straight a space equals space fraction numerator Cα space cross times space Cα over denominator straight C minus Cα end fraction space equals space fraction numerator straight C squared straight alpha squared over denominator straight C left parenthesis 1 minus straight alpha right parenthesis end fraction equals space fraction numerator Cα squared over denominator 1 minus straight alpha end fraction
or space space space space space space space straight K subscript straight a space equals space Cα to the power of 2 space space space space end exponent space space space space space space space space space space space space space space space space space space space space space open square brackets because space space space 1 space minus space straight alpha space equals space 1 close square brackets
or space space space space space space space space straight alpha squared space equals space straight K subscript straight a over straight C space equals space fraction numerator 1.8 space cross times space 10 to the power of negative 5 end exponent over denominator 0.02 end fraction space equals space 9 space cross times space 10 to the power of negative 4 end exponent
or space space space space space space space space straight alpha space equals space 3 space cross times space 10 to the power of negative 2 end exponent
But space space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space equals space Cα space equals space 0.02 space cross times space 3 space cross times space 10 to the power of negative 2 end exponent
space space space space space space space space space space space space space space space space space space equals space 6 space cross times space 10 to the power of 4 space mol space straight L to the power of negative 1 end exponent space space space space space space space space space
    Question 198
    CBSEENCH11006497

    At 298K, 0·01M solution of acetic acid is 1·34% ionised. What is the ionisation constant Ka for acetic acid?

    Solution

    Initial concentration of acetic acid = 0·1 M
    As the degree of ionisation is 1·34% thus amount of acetic acid ionised
                                   equals space fraction numerator 1.34 over denominator 100 end fraction cross times 0.1 space equals space 0.00134 space mol
    Thus we have,
    CH3COOH   rightwards harpoon over leftwards harpoon with Water on top      CH3COO-(aq)   + H3O+
    Initial conc    
    0.1 M                       0                    0
    Equilibrium conc 
    0.1 - 0.00134          0.00134 M           0.00134M
    = 0.9866 M
    Applying the law of chemical equilibrium,
                                    straight K subscript straight a space equals space fraction numerator open square brackets CH subscript 3 COO to the power of minus left parenthesis aq right parenthesis close square brackets space open square brackets straight H subscript 3 straight O to the power of plus close square brackets over denominator open square brackets CH subscript 3 COOH close square brackets end fraction
    Substituting the values, we have,
      straight K subscript straight a space equals space fraction numerator 0.00134 space cross times space 0.00134 over denominator 0.09866 end fraction space equals space 1.72 space cross times space 10 to the power of negative 5 end exponent
             

    Question 199
    CBSEENCH11006498

    Discuss in brief Arrhenius concept of acids and bases.

    Solution
    Acid: According to Arrhenius an acid is a hydrogen-containing substance which dissociates to give hydrogen ions (H+) in its aqueous solution. For example substances such as HCl, HNO3, CH3COOH are acids.
    HCl space rightwards harpoon over leftwards harpoon with Water on top space straight H to the power of plus left parenthesis aq right parenthesis space plus space Cl to the power of minus left parenthesis aq right parenthesis
CH subscript 3 COOH space rightwards harpoon over leftwards harpoon with Water on top space straight H to the power of plus left parenthesis aq right parenthesis space plus space CH subscript 3 COO to the power of minus left parenthesis aq right parenthesis
space space In space general comma space space space HA space rightwards harpoon over leftwards harpoon with Water on top space space straight H to the power of plus left parenthesis aq right parenthesis space plus space straight A to the power of minus left parenthesis aq right parenthesis
    Acids such as HCl and HNO3 which are almost completely ionised in aqueous solutions are known as strong acids,  whereas acids such as CH3COOH which are weakly ionised are called weak acids.
    Base: According to Arrhenius, the base is a substance containing one or more hydroxide groups which dissociate to give hydroxyl ions (OH) in its aqueous solution.For example substances such as NaOH, KOH, Ca(OH)2 are bases.
    Question 200
    CBSEENCH11006499

    What is the fate of proton in aqueous medium?

    Solution
    Proton is simply a hydrogen ion. A naked proton cannot exist as such in the aqueous solution because of its vanishingly small size. Due to its small size and very high charge density, it has strong tendency to interact with water molecules and gets hydrated.
    space straight H to the power of plus space plus space straight H subscript 2 straight O space space space rightwards arrow space space space straight H subscript 3 straight O to the power of plus

    Question 201
    CBSEENCH11006500

    What are the limitations of Arrhenius theory of acid and bases?

    Solution

    (i)  Limited scope: Arrhenius concept is limited to aqueous medium only. It fails to explain the behaviour of acids and bases in a non-aqueous solvent like ammonia,sulphur dioxide,alcohol, etc.
    (ii) According to Arrhenius, the acidic and basic properties are due to H+ and OHions respectively. However, these ions do not exist as such that readily get hydrated and represented as H+ (aq) and OH (aq).

    (iii) It fails to explain the acidic nature of CO2, SO2, SO3, N2O5 which do not contain any hydrogen.

    (iv) It fails to explain the basic nature of CaO, NH3,Na2CO3 which do not contain any hydroxyl group.

    Question 202
    CBSEENCH11006501

    Define neutralisation according to Arrhenius concept.

    Solution
    According to Arrhenius concept, neutralisation is the process in which hydrogen ions and hydroxide ions join to form unionised molecules of water.
     NaOH space space space rightwards arrow space space space Na to the power of plus space plus space OH to the power of minus
HCl space space space space space space space rightwards arrow space space space straight H to the power of plus space plus space Cl to the power of minus
    or space space space space Na to the power of plus space plus space OH to the power of minus plus space space straight H to the power of plus space plus space Cl to the power of minus space space space space rightwards arrow space space space Na to the power of plus space plus space Cl to the power of minus space plus space straight H subscript 2 straight O
or space space space space space straight H to the power of plus OH to the power of minus space space space rightwards arrow space space space straight H subscript 2 straight O
    As a result of neutralisation, the characteristic properties of acids and bases are destroyed.
    Question 203
    CBSEENCH11006502

    Discuss the Lowry Bronsted concept of acids and bases.
    Or
    Discuss the protonic concept of acids and bases.

    Solution
    Acid is defined as any substance (molecule or ion) that is capable of donating a proton to any other substance.
    The base is regarded as any substance (molecule or ion) that is capable of accepting a proton given off by ah acid. Hence, acid is proton donor, Base is proton acceptor.
    example colon space HCl comma space CH subscript 3 COOH comma space NH subscript 4 superscript plus comma space which space are space
capable space of space donating space protons space are space termed space as space acids.
HCl space space plus space straight H subscript 2 straight O space rightwards harpoon over leftwards harpoon space straight H subscript 3 straight O to the power of plus space plus Cl to the power of minus
NH subscript 4 superscript plus space plus straight H subscript 2 straight O space rightwards harpoon over leftwards harpoon space straight H subscript 3 straight O to the power of plus space plus NH subscript 3
Ammonia space and space CO subscript 3 superscript 2 minus end superscript space ions space are space bases space because space they space accept space protons.
straight H subscript 2 straight O space plus NH subscript 3 space rightwards harpoon over leftwards harpoon space NH subscript 4 superscript plus space plus OH to the power of minus
straight H subscript 2 straight O space plus CO subscript 3 superscript 2 minus end superscript space rightwards harpoon over leftwards harpoon space HCO subscript 3 superscript minus space plus OH to the power of minus
    Thus, acid-base reactions are regarded as proton transfer processes. It should be noted that a species can act as an acid (donating proton) only if another species capable of accepting a proton (base) is also present e.g. in the reaction
    straight H subscript 2 straight O space plus space HCl space space space rightwards harpoon over leftwards harpoon space space space straight H subscript 3 straight O to the power of plus space plus space space Cl to the power of minus
    the water molecule acts as a base because it accepts a proton donating by HCl. HCl in benzene or carbon tetrachloride is not an acid because benzene or CCldoes not accept a proton from HCl.
    Question 204
    CBSEENCH11006503

    What do you understand by conjugate acid base pairs? Give examples.

    Solution

    A species formed by adding a proton to Bronsted base is called conjugate acid and a species formed by losing a proton from Bronsted acid is called conjugate base. 
    Brosted space plus space straight H to the power of plus space space space rightwards arrow space space space space Conjugate space acid space space
space space space Bronsted space acid space space space rightwards arrow space space space space space straight H to the power of plus space plus space Conjugate space base
    Thus, every acid has its conjugate base and every base has its conjugate acid. Consider a reaction between HCl and H2O.
    HCl with acid below space plus space stack straight H subscript 2 straight O with base below space space space space leftwards harpoon over rightwards harpoon space space stack straight H subscript 3 straight O to the power of plus with acid below space plus space stack Cl to the power of minus with base below
    In the forward reaction, HCl donates a proton to water.
    ∴  HCl is an acid and H2O is a base.
    In the backward reaction, H3O+ ion donates a proton to Cl ion.
    ∴    H3O+ is an acid and Cl is a base.
    Thus Cl ion is a conjugate base of HCl and H3Ois the conjugate acid of base H2O. Such pairs of substances which differ from one another by a proton are known as conjugate acid-base pairs. Thus any acid-base reaction really involves two acids and two bases, forming conjugate pairs.

    Question 206
    CBSEENCH11006505
    Question 207
    CBSEENCH11006506

    State the formula and name of conjugate acid of the following bases:
    (i) OH               left parenthesis ii right parenthesis space HPO subscript 4 superscript 2 minus end superscript
    left parenthesis iii right parenthesis space straight H subscript 2 PO subscript 4 superscript minus space space space space space space space space space space left parenthesis iv right parenthesis space space CH subscript 3 NH subscript 2

     

    Solution

    Given species       Conjugate acid                Name 
    left parenthesis straight i right parenthesis space space OH to the power of minus space space space space space space space space space space space space space space space space space space straight H subscript 2 straight O space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space Water
left parenthesis ii right parenthesis space HPO subscript 4 superscript 2 minus end superscript space space space space space space space space space space space space space space space straight H subscript 2 PO subscript 4 superscript minus space space space space space space space space space space space space space space space space space space space space space space space space space space space space Dihydrogen space phosphate space ion
left parenthesis iii right parenthesis straight H subscript 2 PO subscript 4 superscript minus space space space space space space space space space space space space space space space space straight H subscript 3 PO subscript 4 space space space space space space space space space space space space space space space space space space space space space space space space space space space space Phosphoric space acid space space space
left parenthesis iv right parenthesis space CH subscript 3 NH subscript 2 space space space space space space space space space space space space CH subscript 3 NH subscript 3 space space space space space space space space space space space space space space space space space space space space space space space space space space Methyl space ammonium space ion space space space space space space space space space space space space space space space

    Question 209
    CBSEENCH11006508

    What is meant by the conjugate acid-base pair? Find the conjugate acid/base for the following species:
    HNO subscript 2 comma space space CN to the power of minus comma space space space HClO subscript 4 comma space space space straight F to the power of minus comma space space space OH to the power of minus comma space space CO subscript 3 superscript 2 minus end superscript space and space straight S to the power of 2 minus end exponent.

    Solution
    An acid-base pair which differs by a proton is called conjugate acid-base pair.
    Species space space space space space space space space space space space space Conjugate space base
HNO subscript 2 space space space space space space space space space space space space space space space space space space space NO subscript 2 superscript minus
HClO subscript 4 space space space space space space space space space space space space space space space space space space ClO subscript 4 superscript minus
CN to the power of minus space space space space space space space space space space space space space space space space space space space space HCN
straight F to the power of minus space space space space space space space space space space space space space space space space space space space space space space space HF
OH to the power of minus space space space space space space space space space space space space space space space space space space space space straight H subscript 2 straight O
CO subscript 3 superscript 2 minus end superscript space space space space space space space space space space space space space space space space space HCO subscript 3 superscript minus
straight S to the power of 2 minus end exponent space space space space space space space space space space space space space space space space space space space HS to the power of minus

    Question 213
    CBSEENCH11006512

    Identify the acids and bases in the following equilibrium reactions:

    straight i right parenthesis space HCl plus space straight H subscript 2 straight O space rightwards harpoon over leftwards harpoon space straight H subscript 3 straight O to the power of plus space plus Cl to the power of minus
ii right parenthesis space HNO subscript 3 space plus straight H subscript 2 straight O space rightwards harpoon over leftwards harpoon space straight H subscript 3 straight O to the power of plus space plus NO subscript 3 superscript minus
iii right parenthesis space CO subscript 3 superscript 2 minus end superscript space plus straight H subscript 2 straight O space rightwards harpoon over leftwards harpoon space OH to the power of minus space plus HCO subscript 3 superscript minus

    Solution
    left parenthesis straight i right parenthesis space HCl with acid below space plus space space stack straight H subscript 2 straight O with base below space space space leftwards harpoon over rightwards harpoon space space space stack straight H subscript 3 straight O to the power of plus with acid below space space plus space stack Cl to the power of minus with base below
    HCl and H3O+ ions are acids as both have the tendency to donate a proton. H2O and Clions are bases as both have the tendency to accept a proton.
    left parenthesis ii right parenthesis space stack HNO subscript 3 with acid below space plus space stack straight H subscript 2 straight O with base below space space space rightwards harpoon over leftwards harpoon space space space space stack straight H subscript 3 straight O to the power of plus with acid below space plus space space stack NO subscript 3 superscript minus with base below
    HNO3 and H3O+ ions are acids as both have the tendency to donate a proton.
    H2O and HO3 ions are bases as both have the tendency to accept a proton.
    left parenthesis iii right parenthesis space stack CO subscript 3 superscript 2 minus end superscript with base below space plus space stack space straight H subscript 2 straight O with acid below space space space rightwards harpoon over leftwards harpoon space space space space space space stack OH to the power of minus with base below space plus space stack HCO subscript 3 superscript minus with acid below
    CO subscript 3 superscript 2 minus end superscript space and space OH to the power of minus  ions are bases as both have the tendency to accept a proton.
    Question 215
    CBSEENCH11006514

    Describe how water behaves both as an acid or a base.

    Solution
    H2O can donate a proton (acting as acid) and accept a proton (acting as a base).
    (i) Water acting as an acid.
    stack straight H subscript 2 straight O with acid below space plus space stack NH subscript 3 with base below space space space rightwards harpoon over leftwards harpoon space space space space space NH subscript 4 superscript plus space plus space OH to the power of minus
stack straight H subscript 2 straight O with acid below space plus space stack CO subscript 3 superscript 2 minus end superscript with base below space space space space leftwards harpoon over rightwards harpoon space space space space HCO subscript 3 superscript minus space plus space OH to the power of minus
    (ii) Water acting as a base
      stack space space straight H subscript 2 straight O with a c i d below space plus space stack CH subscript 3 COOH with base below space space space leftwards harpoon over rightwards harpoon space space straight H subscript 3 straight O to the power of plus space plus space CH subscript 3 COO to the power of minus
space space stack straight H subscript 2 straight O with base below space plus space HCl with acid below space space space leftwards harpoon over rightwards harpoon space space space space straight H subscript 3 straight O to the power of plus space space plus space Cl to the power of minus
    Question 216
    CBSEENCH11006515

    Comment on the statement: Strong acid has a weak conjugate base and vice-versa.

    Solution

    According to Bronsted Lowry concept:
    (i) the strength of an acid depends on upon its tendency to donate proton and
    (ii) the strength of base depends on upon its tendency to accept a proton.
    Consider a reaction between HNO3 and water.
    stack HNO subscript 3 with Strong space acid below space plus space stack straight H subscript 2 straight O with Strong space base space below space space space space leftwards harpoon over rightwards harpoon space space space space space space stack straight H subscript 3 straight O to the power of plus with Weak space acid below space space space plus space stack NO subscript 3 superscript minus with Weak space base below
    HNO3 has a greater tendency to donate a proton than H3O+ ion. Therefore. HNO3 is a strong acid, NO3 ion has a very little tendency to accept a proton, therefore, NO3 ion is a weak base.
    Strong space acid space space space rightwards harpoon over leftwards harpoon space space space straight H to the power of plus space plus space Weak space conjugate space base.
    Thus strong acid has a weak conjugate base. 
    Now consider the reaction between acetic acid and water.
       stack CH subscript 3 COOH with Weak space acid below space plus space stack straight H subscript 2 straight O with Weak space base below space space space leftwards harpoon over rightwards harpoon space space space stack straight H subscript 3 straight O to the power of plus with Strong space acid below space plus space space stack CH subscript 3 COO to the power of minus with Strong space base below
    Acetic acid has a small tendency to donate a proton, therefore,  it is a weak acid. CH3COO– ion has strong tendency to accept a proton, therefore, CH3COO ion is a strong base.
    Weak space acid space space space rightwards harpoon over leftwards harpoon space space space straight H to the power of plus space plus space Strong space conjugate space base
    Thus weak acid has a strong conjugate base.

    Question 217
    CBSEENCH11006516

    All Arrhenius acids are Bronsted acids while all Arrhenius bases arc not Bronsted bases. Discuss.

    Solution

    All Arrhenius acids are Bronsted acids: According to Arrhenius, an acid is a substance that yields hydrogen ions in an aqueous solution. According to Bronsted concept, an acid is a substance that can donate a proton (H+ ion). Both definitions require an acid to be a source of protons. Thus HCl is an acid according to both the theories. Therefore, all Arrhenius acids are also Bronsted acids.

    All Arrhenius bases are not Bronsted bases: According to Arrhenius concept, a base is a substance that dissociates in aqueous solution to give hydroxyl ions. According to Bronsted concept, a base is a substance that accepts a proton, e.g. NaOH is a base according to Arrhenius concept because it yields OH ions in aqueous solution.
    NaOH space space space rightwards harpoon over leftwards harpoon with Water on top space space Na to the power of plus left parenthesis aq right parenthesis space plus space OH to the power of minus left parenthesis aq right parenthesis
    But NaOH does not accept a proton as such, thus it is not a base according to Bronsted concept. Therefore, all Arrhenius bases are not Bronsted bases.

    Question 218
    CBSEENCH11006517

    What are the limitations (drawbacks) of Bronsted-Lowry concept of acids and bases?

    Solution

    (i) It fails to explain the reaction between acidic oxides (SO2, SO3 etc.) and basic oxides (BaO, CaO, Na2O etc.) because, in such reactions, no proton transfer occurs.
    (ii) It fails to recognise the acidic character of FeCl3, AlCl3 BF3 etc.

    Question 219
    CBSEENCH11006518

    Discuss in brief Lewis concept of acids and bases.
    Or
    Discuss the electronic concept of acids and bases.

    Solution

    According to Lewis concept, an acid is any substance (atom, molecule or ion) which is capable of accepting a pair of electrons from another substance to form a co-ordinate (dative) bond.
    A base is any substance (atom, molecule or ion) which is capable of donating a pair of electrons to form a co-ordinate (dative) bond. Hence,
    open table attributes columnalign right end attributes row cell Acid space is space an space electron space pair space acceptor end cell row cell Base space is space an space electron space pair space donor end cell end table close curly brackets space space Electronic space concept
    In terms of electronic structure. 

    (i) an acid must have a vacant orbital into which an electron pair donated by a base can be accommodated e.g. AlCl3, BF3 
    (ii) a base is a substance which has at least one lone pair of electrons e.g




    Question 220
    CBSEENCH11006519

    Classify the following species into Lewis acids and Lewis bases and show how these act as Lewis acid/base:
    (a) O (b) F (c) H+ (d) BCl3

    Solution

    (a) OH can donate electron pair. Hence it is a Lewis base.
    (b) F– can also donate electron pair. Hence it is a Lewis base.
    (c) H+ can accept electron pair. Hence it is a Lewis acid.
    (d) BCl3 is deficient in electrons. Hence it can accept electron pair and is, therefore, a Lewis acid.

    Question 221
    CBSEENCH11006520

    How does Lewis concept account for the acidic character of carbon dioxide?

    Solution
    The molecule is linear and is represented as O = C = O. Under the influence of attacking Lewis base such as OH, one electron pair from the multiple bonds gets shifted towards the oxygen atom (oxygen is more electronegative than carbon). As a result, the carbon atom in CO2 becomes electron deficient and thus it acts as Lewis acid.

    Question 222
    CBSEENCH11006521

    What are the limitations of Lewis concept of acids and bases ?

    Solution

    (i) The concept fails to recognise the relative strength of acids and bases.
    (ii) Formation of a coordination compound is a slow process but acid-base reactions are fast. This concept could not explain this behaviour. 
    (iii) Protonic acids (H2SO4, HCl, HNO3) do not form a coordinate bond with bases and therefore are not included in the Lewis acids.
    (iv) The catalytic activity of many acids is due to H+ ion. Since a Lewis acid need not contain hydrogen hence many Lewis acids will not have catalytic activity.

    Question 223
    CBSEENCH11006522

    Justify the statement: All Bronsted bases are Lewis bases, but all Bronsted acids are not Lewis acids.

    Solution
    (i) All Bronsted bases are also Lewis bases: According to Bronsted concept, the base is a substance which accepts a proton. According to Lewis concept, a base is a substance which can donate a pair of electron. Any substance which can donate a pair of an electron can easily accept a proton.

    Thus all Bronsted bases are all Lewis bases.
    (ii) All Bronsted acids are not Lewis acids: According to Bronsted concept, an acid is a substance that can donate a proton (H+). According to Lewis concept, an acid is any substance (molecule or ion) which can accept a pair of electrons from another substance to form a coordinate bond. HCl, H2SO4 are Bronsted acids because they can donate protons, but they cannot accept a pair of electrons to form a coordinate bond, therefore, they are not Lewis acids. Thus all Bronsted acids are not Lewis acids.
    Question 224
    CBSEENCH11006523

    Out of Lowry Bronsted concept and Lewis concept, which is regarded as better and why?

    Solution

    Lewis concept of acids and basis is regarded as better than Bronsted concept due to the following reasons:
    (i) Many species which are acids and bases according to Bronsted and Arrhenius concept are also covered by Lewis concept.
    (ii) The acidic and basic character of certain species can be explained only with the help of Lewis concept. For example, acidic nature of CO2 and basic nature of CaO can not be explained by any other concept except the Lewis concept.
    (iii) According to Lewis concept, an acid need not contain the element hydrogen but it must be electron deficient in nature. For example AlCl3 is an acid though it has no H+ion present.

    Question 225
    CBSEENCH11006524

    What do you understand by ionic product of water?

    Solution
    Water is a weak electrolyte. It dissociates to small extent to give H3O+ (aq) and OH (aq) ions as represented below:
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#13 {main}</pre>
    Applying the law of chemical equilibrium,
           straight K space equals space fraction numerator open square brackets straight H subscript 3 straight O to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets over denominator open square brackets straight H subscript 2 straight O close square brackets squared end fraction
    Since the degree of dissociation of water is low, so its concentration remains practically unchanged. Thus [H2O] may be taken as constant.
    K × [H2O]2 = [H3O+][OH]
    or Kw = [H3O+][OH]
    where KM,is constant and is known as an ionic product of water. It may be defined as the product of the hydronium ion concentration and hydroxyl ion concentration at a given temperature. The value of Kw at 298K is 1·008 × 10–14 mol2 L–2.
    For space pure space water space left square bracket straight H subscript 3 straight O to the power of plus right square bracket space equals left square bracket OH to the power of minus right square bracket
we space know comma
left square bracket straight H subscript 3 straight O to the power of plus right square bracket left square bracket OH to the power of minus right square bracket space equals space straight K subscript straight H equals space 1 space straight x space 10 to the power of negative 14 end exponent
or space
left square bracket straight H subscript 3 straight O to the power of plus right square bracket squared equals space 1 space straight x 10 to the power of negative 14 end exponent
or
left square bracket straight H subscript 3 straight O to the power of plus right square bracket space equals square root of 1 space straight x 10 to the power of negative 14 end exponent space end root space
space equals 1 space straight x space 10 to the power of negative 7 end exponent space mol space straight L to the power of negative 1 end exponent
Hence space for space pure space water space left square bracket straight H subscript 3 straight O to the power of plus right square bracket
equals space left square bracket OH to the power of minus right square bracket space equals 1 space straight x space 10 to the power of negative 7 end exponent space mol space straight L to the power of negative 1 end exponent


    Question 226
    CBSEENCH11006525

    What is the effect of temperature on (ionic product of water)?

    Solution
    The dissociation of water is an endothermic reaction.
    2 straight H subscript 2 straight O left parenthesis straight l right parenthesis space space rightwards harpoon over leftwards harpoon space space space straight H subscript 3 straight O to the power of plus left parenthesis aq right parenthesis space plus space OH to the power of minus left parenthesis aq right parenthesis semicolon space space increment straight H space equals space 57.1 space kJ
    According to Le-Chatelier’s principle, an increase in temperature will shift the equilibrium towards that direction where absorption of heat (endothermic change) takes place in order to nullify the effect of the rise in temperature i.e. equilibrium shifts in the forward direction producing a large concentration of H3O+ and OH ions. Hence Kw increases with the rise in temperature.
    Question 227
    CBSEENCH11006526

    The ionic product of water is 0·11 × 10–14 at 273 K; 1·0 × 10–14 at 298K and 51 × 10–14 at 373K. Deduce from this data whether the ionisation of water into hydrogen and hydroxide ion is exothermic or endothermic.

    Solution
    Water space ionises space as space straight H subscript 2 straight O space space rightwards harpoon over leftwards harpoon space space space straight H to the power of plus space plus space OH to the power of minus
    From the given data for the ionic product of water at different temperature, it is clear that ionic product of water increases with the increase in temperature. Ionic product of water is the product of [H+] and [OH], this means that with the increase in temperature H+ and OH increase. In other words, increase in temperature favours the forward reaction. This is possible only for the endothermic reaction according to Le-Chatelier’s principle. Hence ionisation of water to [H+] and [OH] is an endothermic reaction.
    Question 228
    CBSEENCH11006527

    Comment on the statement: An acidic solution contains OH ions and even a basic solution contains H3O+ ions.
    Or
    How the values of Kw, [H3O+] and [OH] are affected if acid or base is added to pure water at 298K?

    Solution

    We know, [H3O+][OH] = Kw
    For pure water, [H3O+] =[OH]
    = 1 × 10–7 mol L–1
    On adding few drops of an acid (say HCl) to water, the concentration of H3O+ increases and thus concentration OH decreases accordingly in order to maintain Kw constant.
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#4 [internal function]: haxe_Http_5(true, Object(com_wiris_plugin_impl_HttpImpl), Object(com_wiris_plugin_impl_HttpImpl), Array, Object(haxe_io_BytesOutput), true, 'Http Error #404')
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('haxe_Http_5', Array)
#6 [internal function]: _hx_lambda->execute('Http Error #404')
#7 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(27): call_user_func_array(Array, Array)
#8 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(444): com_wiris_plugin_impl_HttpImpl->onError('Http Error #404')
#9 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(458): haxe_Http->customRequest(true, Object(haxe_io_BytesOutput), NULL, NULL)
#10 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(40): haxe_Http->request(true)
#11 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(80): com_wiris_plugin_impl_HttpImpl->request(true)
#12 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#13 {main}</pre>
    Hence acidic solution contains both hydronium and hydroxyl ions. But open vertical bar straight H subscript 3 straight O to the power of plus close vertical bar space greater than space open vertical bar OH to the power of minus close vertical bar But on adding. 
    But on adding few drops of a base (say NaOH) to water, the concentration of OHincreases and thus the concentration of H3O+ decreases accordingly in order to maintain Kw constant.
    NaOH space space rightwards harpoon over leftwards harpoon space space space space Na to the power of plus space plus space space OH to the power of minus
open square brackets straight H subscript 3 straight O to the power of plus close square brackets space equals space fraction numerator straight K subscript straight w over denominator open square brackets OH to the power of minus close square brackets end fraction
    Hence basic solution contains both hydronium and hydroxyl ions.
    But [H3O+] < [OH]
    In general, in neutral solution,
    [H3O+] = [OH]
    In acidic solution, [H3O+] > [OH]
    In basic solution, [H3O+] < [OH]

     

    Question 229
    CBSEENCH11006528

    What do you mean by pH value?

    Solution
    Sorensen in 1909 suggested a convenient method of expressing hydronium ion concentration known as pH scale. The pH of a solution may be defined as the numerical value of the negative power of which 10 must be raised in order to express hydronium ion concentration i.e.
              open square brackets straight H subscript 3 straight O to the power of plus close square brackets space equals space 10 to the power of negative pH end exponent
    Taking logarithm on both the sides,
                      log space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space equals space minus pH space log space 10
    or                        pH space equals space minus log space open square brackets straight H subscript 3 straight O to the power of plus close square brackets
    Thus pH of a solution may also be defined as the negative logarithm of hydronium ion concentration.
    Also,  
     pH space equals space log space fraction numerator 1 over denominator open square brackets straight H subscript 3 straight O to the power of plus close square brackets end fraction
    Hence pH of a solution is defined as the logarithm of the reciprocal of hydronium ion concentration.
    left parenthesis straight i right parenthesis space For space pure space water space and space for space other space neutral space solution colon
space space space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space equals space 1 space cross times space 10 to the power of negative 7 end exponent space mol space straight L to the power of negative 1 end exponent
therefore space space space space pH space equals space minus log space open square brackets straight H subscript 3 straight O to the power of plus close square brackets
space space space space space space space space space space space space equals negative log space left parenthesis 1 space cross times space 10 to the power of negative 7 end exponent right parenthesis space equals space minus left parenthesis negative 7 right parenthesis space log space 10
space space space space space space space space space space space space space equals space plus 7 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space left square bracket because space log space 10 space equals space 1 right square bracket
    <pre>uncaught exception: <b>Http Error #404</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php line 61<br />#0 [internal function]: com_wiris_plugin_impl_HttpImpl_0(Object(com_wiris_plugin_impl_HttpImpl), NULL, 'http://www.wiri...', 'Http Error #404')
#1 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('com_wiris_plugi...', Array)
#2 [internal function]: _hx_lambda->execute('Http Error #404')
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(532): call_user_func_array(Array, Array)
#4 [internal function]: haxe_Http_5(true, Object(com_wiris_plugin_impl_HttpImpl), Object(com_wiris_plugin_impl_HttpImpl), Array, Object(haxe_io_BytesOutput), true, 'Http Error #404')
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('haxe_Http_5', Array)
#6 [internal function]: _hx_lambda->execute('Http Error #404')
#7 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(27): call_user_func_array(Array, Array)
#8 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(444): com_wiris_plugin_impl_HttpImpl->onError('Http Error #404')
#9 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(458): haxe_Http->customRequest(true, Object(haxe_io_BytesOutput), NULL, NULL)
#10 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(40): haxe_Http->request(true)
#11 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(80): com_wiris_plugin_impl_HttpImpl->request(true)
#12 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#13 {main}</pre>

    As pH of a solution goes on decreasing below 7, the acidic nature of solution goes on increasing.
    If pH lies between:
    (a) 0 and 2, the solution is strongly acidic,
    (b) 2 and 4, the solution is moderately acidic,
    (c) 4 and 7, the solution is weakly acidic.
    (iii) In basic solution:
    open square brackets straight H subscript 3 straight O close square brackets to the power of plus space less than space 1 space cross times space 10 to the power of negative 7 end exponent space mol space straight L to the power of negative 1 end exponent space such space as space 10 to the power of negative 8 end exponent comma space 10 to the power of negative 9 end exponent comma space 10 to the power of negative 10 end exponent space mol space straight L to the power of negative 1 end exponent
    We space know comma space space space pH space equals space minus log space open square brackets straight H subscript 3 straight O to the power of plus close square brackets
therefore space space space space space space pH thin space greater than 7 space such space as space 8 comma space 9 comma space 10 space etc.
      
    As pH of a solution goes on increasing above 7, the basic nature of the solution goes on increasing.

    If pH lies between:
    (a) 7 and 10, the solution is weakly basic,
    (b) 10 and 12, the solution is moderately basic,
    (c) 12 and 14, the solution is strongly basic.

    Question 230
    CBSEENCH11006529

    What is the effect of temperature on pH?

    Solution

    We know that ionic product of water (Kw.) increases with the rise of temperature. Therefore, the concentration of H3O+ ions increases with temperature.
    pH space equals space log space fraction numerator 1 over denominator open square brackets straight H subscript 3 straight O to the power of plus close square brackets end fraction
    Therefore, pH value is inversely proportional to straight H subscript 3 straight O to the power of plus ion concentration
    Hence pH value decreases with the rise in temperature.

    Question 231
    CBSEENCH11006530

    What is the significance (or importance) of pH value?

    Solution

    The significance of the pH value. pH is a measure of the acidic or basic (alkaline) nature of a solution (concentration of the hydrogen ion [H+] activity in a solution determines the pH).
    For neutral solution: pH = 7
    For acidic solution: pH < 7
    For basic solution: pH > 7
    Certain chemical reactions take place at a fixed pH value e.g. fresh cow’s milk (pH = 6·4) turns to the presence of acids produced by the bacteria. The sour milk has a pH 3 to 4.

    Question 232
    CBSEENCH11006531

    What is pOH of a solution? How is it related to its pH value?

    Solution
    The pOH of a solution may be defined as the negative logarithm of its OH ion concentration.
    <pre>uncaught exception: <b>Http Error #404</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php line 61<br />#0 [internal function]: com_wiris_plugin_impl_HttpImpl_0(Object(com_wiris_plugin_impl_HttpImpl), NULL, 'http://www.wiri...', 'Http Error #404')
#1 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('com_wiris_plugi...', Array)
#2 [internal function]: _hx_lambda->execute('Http Error #404')
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(532): call_user_func_array(Array, Array)
#4 [internal function]: haxe_Http_5(true, Object(com_wiris_plugin_impl_HttpImpl), Object(com_wiris_plugin_impl_HttpImpl), Array, Object(haxe_io_BytesOutput), true, 'Http Error #404')
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('haxe_Http_5', Array)
#6 [internal function]: _hx_lambda->execute('Http Error #404')
#7 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(27): call_user_func_array(Array, Array)
#8 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(444): com_wiris_plugin_impl_HttpImpl->onError('Http Error #404')
#9 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(458): haxe_Http->customRequest(true, Object(haxe_io_BytesOutput), NULL, NULL)
#10 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(40): haxe_Http->request(true)
#11 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(80): com_wiris_plugin_impl_HttpImpl->request(true)
#12 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#13 {main}</pre>
    Relation between pH and pOH:
    We space know comma space space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets space equals space straight K subscript straight w space equals space 1 space cross times space 10 to the power of negative 14 end exponent
    Taking logarithm on both sides,
    log space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space space plus space log space open square brackets OH to the power of minus close square brackets space equals space log space left parenthesis 1 space cross times space 10 to the power of negative 14 end exponent right parenthesis
log space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space plus space log space open square brackets OH to the power of minus close square brackets space equals space minus 14 space
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space log space 10 space equals space 1 close square brackets
or space space space space space space minus log space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space minus space log space open square brackets OH to the power of minus close square brackets space space equals space 14
or space space space space space space space space space space space space space space space space space space pH space plus space pOH space equals space 14
space space space space space space space space space space space space space space
    Question 235
    CBSEENCH11006534

    Ionic product of water at 310K is 2·7 × 10–14. What is the pH of neutral water at this temperature? 

    Solution
    Ionic product of water (Kw)
                        equals 2.7 space cross times space 10 to the power of negative 14 end exponent
    We space know comma space open square brackets straight H to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets space equals space straight K subscript straight w
For space pure space water comma
space space space space space space space space space space open square brackets straight H to the power of plus close square brackets space equals space open square brackets OH to the power of minus close square brackets
therefore space space space space space space open square brackets straight H to the power of plus close square brackets squared space equals space straight K subscript straight w space equals space 2.7 space space cross times space 10 to the power of negative 14 end exponent
or space space space space space space open square brackets straight H to the power of plus close square brackets space equals space square root of 2.7 space cross times space 10 to the power of negative 14 end exponent end root space equals space 1.6 space cross times space 10 to the power of negative 7 end exponent space mol space straight L to the power of negative 1 end exponent
    pH space equals space minus log space open square brackets straight H to the power of plus close square brackets
space space space space space equals space minus log space open square brackets 1.6 space cross times space 10 to the power of negative 7 end exponent close square brackets
space space space space space equals space minus open square brackets log space 1.6 space plus space log space 10 to the power of negative 7 end exponent close square brackets
space space space space space equals space minus open square brackets 0.2041 space minus space 7 close square brackets space space space open square brackets because space log space 10 space equals space 1 close square brackets
space space space space space equals space 7 minus 0.2041
space space space space space equals space 6.7959 space asymptotically equal to space 6.8
    Question 236
    CBSEENCH11006535

    The concentration of hydrogen ion in a sample of soft drink is 3·8 × 10-3 M. What is its pH value?

    Solution
    We know,
    pH space equals space minus log space open square brackets straight H to the power of plus close square brackets
space space space space equals space minus log space open square brackets 3.8 space cross times space 10 to the power of negative 3 end exponent close square brackets
space space space space equals space minus open square brackets log space 3.8 space plus space log space 10 to the power of negative 3 end exponent close square brackets
space space space space equals space minus open square brackets 0.58 minus 3 close square brackets
space space space space space equals space 2.42
    Since pH of the soft drink is 2.42, therefore,  it is acidic.
    Question 238
    CBSEENCH11006537

    Assuming complete dissociation, calculate the pH of the following solution:
    0.005M NaOH

    Solution

    0.005 M NaOH:
    Since NaOH is completely dissociated,
    therefore space space space space open square brackets OH to the power of minus close square brackets space equals space 0.005 space straight M space equals space 5 space cross times space 10 to the power of negative 3 end exponent straight M
Also space space space open square brackets straight H to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets space equals space 1 space cross times space 10 to the power of negative 14 end exponent
therefore space space space space space open square brackets straight H to the power of plus close square brackets space equals space fraction numerator 1 space cross times space 10 to the power of negative 14 end exponent over denominator open square brackets OH to the power of minus close square brackets end fraction space equals space fraction numerator 1 space cross times space 10 to the power of negative 14 end exponent over denominator 5 space cross times space 10 to the power of negative 3 end exponent end fraction
space space space space space space space space space space space space space space space space equals space 2 space cross times space 10 to the power of negative 12 end exponent straight M
    therefore space space space pH space equals space minus log space open square brackets straight H to the power of plus close square brackets
space space space space space space space space space space space equals space minus log space open square brackets 2 space cross times space 10 to the power of negative 12 end exponent close square brackets
space space space space space space space space space space space equals space minus open square brackets log space 2 space plus space log space 10 to the power of negative 12 end exponent close square brackets
space space space space space space space space space space space equals negative open square brackets 0.3010 space minus space 12 close square brackets
space space space space space space space space space space space equals space 11.6990 space asymptotically equal to space 11.70 space space space space space space space space space space space space space space space space space space space space space

    Question 239
    CBSEENCH11006538

    Assuming complete dissociation, calculate the pH of the following solution:
    0·002M HBr

    Solution

    0·002M HBr
    Since HBr is completely dissociated,
    therefore space space space open square brackets straight H to the power of plus close square brackets space equals space 0.002 space straight M space equals space 2 space cross times space 10 to the power of negative 3 end exponent straight M
space space space space space space pH space equals space minus log space open square brackets straight H to the power of plus close square brackets space equals space minus log space open square brackets 2 space cross times space 10 to the power of negative 3 end exponent close square brackets
space space space space space space space space space space space equals space minus open square brackets log space 2 space cross times space space 10 space log space 10 to the power of negative 3 end exponent close square brackets
space space space space space space space space space space equals negative open square brackets 0.3010 space minus space 3 close square brackets space equals space 2.699 space space asymptotically equal to space 2.7 space

    Question 240
    CBSEENCH11006539

    Assuming complete dissociation, calculate the pH of the following solution:
    0.002M KOH

    Solution

    0.002M KOH
    As KOH is completely dissociated,  therefore, 
    open square brackets OH to the power of minus close square brackets space equals space 0.002 space straight M space equals space 2 space cross times space 10 to the power of negative 3 end exponent straight M
Also comma space open square brackets straight H to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets space equals space 1 space cross times space 10 to the power of negative 14 end exponent
therefore space space space space open square brackets straight H to the power of plus close square brackets space equals space fraction numerator 1 space cross times space 10 to the power of negative 14 end exponent over denominator 10 space straight H to the power of negative 1 end exponent end fraction space equals space fraction numerator 1 space cross times space 10 to the power of negative 14 end exponent over denominator 2 space cross times space 10 to the power of negative 3 end exponent end fraction
space space space space space space space space space equals space 5 space cross times space 10 to the power of negative 12 end exponent straight M
    therefore space space pH space equals space minus log space open square brackets straight H to the power of plus close square brackets space equals space minus log space open square brackets 5 space cross times space 10 to the power of negative 12 end exponent close square brackets
space space space space space space space space space space equals space minus space open square brackets 0.6990 minus 12 close square brackets space equals space 11.301

    Question 242
    CBSEENCH11006541

    0·049g H2SO4 acid is dissolved in water to prepare 200 ml solution. Calculate the pH of the solution.

    Solution
    <pre>uncaught exception: <b>Http Error #404</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php line 61<br />#0 [internal function]: com_wiris_plugin_impl_HttpImpl_0(Object(com_wiris_plugin_impl_HttpImpl), NULL, 'http://www.wiri...', 'Http Error #404')
#1 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('com_wiris_plugi...', Array)
#2 [internal function]: _hx_lambda->execute('Http Error #404')
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(532): call_user_func_array(Array, Array)
#4 [internal function]: haxe_Http_5(true, Object(com_wiris_plugin_impl_HttpImpl), Object(com_wiris_plugin_impl_HttpImpl), Array, Object(haxe_io_BytesOutput), true, 'Http Error #404')
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('haxe_Http_5', Array)
#6 [internal function]: _hx_lambda->execute('Http Error #404')
#7 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(27): call_user_func_array(Array, Array)
#8 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(444): com_wiris_plugin_impl_HttpImpl->onError('Http Error #404')
#9 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(458): haxe_Http->customRequest(true, Object(haxe_io_BytesOutput), NULL, NULL)
#10 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(40): haxe_Http->request(true)
#11 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(80): com_wiris_plugin_impl_HttpImpl->request(true)
#12 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#13 {main}</pre>
    Since H2SO4 is strong acid, it is completely dissociated, one mole H2SO4 produces two moles of H+ ions,
    straight H subscript 2 SO subscript 4 space space rightwards arrow with water on top space space 2 straight H to the power of plus left parenthesis aq right parenthesis space plus space SO subscript 4 superscript negative 2 end superscript left parenthesis aq right parenthesis
open square brackets straight H to the power of plus close square brackets space equals space 2 open square brackets straight H subscript 2 SO subscript 4 close square brackets
space space space space space space space space equals space 2 space cross times space 0.0025
space space space space space space space space equals space 0.005 space straight M
space space space space space space space space space equals space 5 space cross times space 10 to the power of negative 3 end exponent straight M
    We space know comma space
space space space pH space equals space minus log space open square brackets straight H to the power of plus close square brackets space equals space minus log space open square brackets 5 space cross times space 10 to the power of negative 3 end exponent close square brackets
space space space space space space space space equals negative open square brackets log space 5 space plus space log space 10 to the power of negative 3 end exponent close square brackets
space space space space space space space space equals negative open square brackets log space 5 space minus space 3 space log space 10 close square brackets
space space space space space space space space equals space minus space open square brackets 0.6990 plus 3 close square brackets
therefore space space pH space equals space 2.301
    Question 245
    CBSEENCH11006544

    Calculate the pH of a 1·0 × 10–8 M solution of HCl.

    Solution
    The [H3O+] is obtained from the following two ionisation reactions:
    left parenthesis straight i right parenthesis space HCl space left parenthesis aq right parenthesis space plus space straight H subscript 2 straight O left parenthesis l right parenthesis space space rightwards harpoon over leftwards harpoon space space space straight H subscript 3 straight O to the power of plus left parenthesis aq right parenthesis space plus space OH to the power of minus left parenthesis aq right parenthesis
left parenthesis ii right parenthesis space 2 straight H subscript 2 straight O space rightwards harpoon over leftwards harpoon space space space space straight H subscript 3 straight O to the power of plus space left parenthesis aq right parenthesis space plus space OH to the power of minus left parenthesis aq right parenthesis
space space space therefore space space space From space acid semicolon space space space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space equals space 10 to the power of negative 8 end exponent straight M
From space water semicolon space space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space equals space open square brackets OH to the power of minus close square brackets space equals space straight x space mol space straight L to the power of negative 1 end exponent left parenthesis aq right parenthesis

    Thus space in space solution comma space we space have
space space space space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space equals space left parenthesis 10 to the power of negative 8 end exponent space plus space straight x right parenthesis space straight M space and space open square brackets OH to the power of minus close square brackets space equals space straight x space straight M
    We know,
     open square brackets straight H subscript 3 straight O to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets space equals straight K subscript straight w space equals space 10 to the power of negative 14 end exponent
    <pre>uncaught exception: <b>Http Error #404</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php line 61<br />#0 [internal function]: com_wiris_plugin_impl_HttpImpl_0(Object(com_wiris_plugin_impl_HttpImpl), NULL, 'http://www.wiri...', 'Http Error #404')
#1 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('com_wiris_plugi...', Array)
#2 [internal function]: _hx_lambda->execute('Http Error #404')
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(532): call_user_func_array(Array, Array)
#4 [internal function]: haxe_Http_5(true, Object(com_wiris_plugin_impl_HttpImpl), Object(com_wiris_plugin_impl_HttpImpl), Array, Object(haxe_io_BytesOutput), true, 'Http Error #404')
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('haxe_Http_5', Array)
#6 [internal function]: _hx_lambda->execute('Http Error #404')
#7 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(27): call_user_func_array(Array, Array)
#8 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(444): com_wiris_plugin_impl_HttpImpl->onError('Http Error #404')
#9 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(458): haxe_Http->customRequest(true, Object(haxe_io_BytesOutput), NULL, NULL)
#10 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(40): haxe_Http->request(true)
#11 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(80): com_wiris_plugin_impl_HttpImpl->request(true)
#12 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#13 {main}</pre>
    straight i. straight e. space open square brackets OH to the power of minus close square brackets space equals space 9.5125 space cross times space 10 to the power of negative 8 end exponent straight M
or space space space space space space straight p subscript OH space equals space minus log space open square brackets OH to the power of minus close square brackets
space space space space space space space space space space space space space space space equals space minus log left parenthesis 9.5125 space cross times space 10 to the power of negative 8 end exponent right parenthesis
space space space space space space space space space space space space space space space equals space 8 minus 0.9783 space equals space 7.02
pH space equals space 14 minus space straight p subscript OH space equals 14 minus 7.02 space equals 6.98
    Question 248
    CBSEENCH11006547
    Question 249
    CBSEENCH11006548

    If 0.561 KOH is dissolved in water to give 200 mL, of the solution at 298 K, calculate the concentration of potassium, hydrogen and hydroxyl ions. What is its pH ?

    Solution
    Strength space of space solution space equals space fraction numerator 0.561 over denominator 200 end fraction cross times 1000 space gL to the power of negative 1 end exponent
space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space 5 space cross times space 0.561 space gL to the power of negative 1 end exponent
Molar space mass space of space KOH space equals space 39.1 space plus 16 space plus space 1
space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space 56.1
Molarity space of space solution space equals space fraction numerator 5 space cross times space 0.561 over denominator 56.1 end fraction
space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space 5 space cross times space 10 to the power of negative 2 end exponent straight M
space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space space 0.05 space straight M
    KOH being a strong base undergoes almost complete ionisation.  
      KOH space stack rightwards arrow space with water on top space space straight K to the power of plus left parenthesis aq right parenthesis space plus space OH to the power of minus left parenthesis aq right parenthesis
therefore space space space space open square brackets OH to the power of minus close square brackets space equals space open square brackets NaOH close square brackets space equals space 0.05 space straight M space equals space 5 space cross times space 10 to the power of negative 2 end exponent straight M
open square brackets straight K to the power of plus close square brackets space equals space 0.05 space straight M
Also space space open square brackets straight H to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets space equals space straight K subscript straight w space equals space 1 space cross times space 10 to the power of negative 14 end exponent
therefore space space space open square brackets straight H to the power of plus close square brackets space equals space fraction numerator 1 space cross times 10 to the power of negative 14 end exponent over denominator 5 space cross times space 10 to the power of negative 2 end exponent end fraction space equals space 2 space cross times space 10 to the power of negative 13 end exponent straight M
Also comma space space pH space equals space minus log space open square brackets straight H to the power of plus close square brackets
                    equals negative space log space open square brackets 2 space cross times space 10 to the power of negative 13 end exponent close square brackets
equals negative open square brackets log space 2 space plus space log space 10 to the power of negative 13 end exponent close square brackets
space equals space minus left square bracket 0.3010 space minus space 13 right square bracket
space equals space 12.699
    Question 250
    CBSEENCH11006549

    Calculate the pH of the resultant mixtures:
    (a) 10 mL of 0·2 M Ca(OH)2 + 25 mL of 0·1M HCl

    (b) 10 mL of 0·01 M H2SO+ 10mLof 0·01 IM Ca(OH)2

    (c) 10mL of 0·1 M H2SO+ 10mL of 0·1 M KOH

    Solution
    left parenthesis straight a right parenthesis space Volume space of space 0.2 space straight M thin space Ca left parenthesis OH right parenthesis subscript 2 space equals space 10 space mL space left parenthesis given right parenthesis
Volume space of space 0.1 space straight M space HCl space equals space 25 space mL space space space left parenthesis given right parenthesis
therefore space space space space straight M left parenthesis OH to the power of minus right parenthesis space equals space fraction numerator straight M subscript 1 straight V subscript 1 left parenthesis Base right parenthesis space minus space straight M subscript 2 straight V subscript 2 left parenthesis Acid right parenthesis over denominator straight V subscript 1 plus straight V subscript 2 end fraction
space space space space space space space space space space space space space space space space space space space space equals space fraction numerator 0.2 space cross times space 2 space cross times space 10 minus space 0.1 space cross times space 2 over denominator 10 plus 25 end fraction
straight M left parenthesis OH to the power of minus right parenthesis space equals space fraction numerator 1.5 over denominator 25 end fraction space equals space 0.06 space equals space 6 cross times 10 to the power of negative 2 end exponent space space space space space space space space space
    But space space space space space space straight p subscript OH space equals space minus log space open square brackets OH to the power of minus close square brackets space equals space minus log space left parenthesis 6 space cross times space 10 to the power of negative 2 end exponent right parenthesis
space space space space space space space space space space space space space space space space space equals negative log space 6 space minus space log space 10 to the power of negative 2 end exponent
space space space space space space space space space space space space space space space space space equals space minus 0.779 space plus space 2
space space space space space space space space space space space space space space space space space equals space 1.221 space space space space space space space space space space space space space space space space space space space space space
    because space space straight p subscript straight H space plus space straight p subscript OH space equals space 14
therefore space space space space space straight p subscript straight H space equals space 14 minus straight p subscript OH
space space space space space space space space space space space space space equals 14 minus 1.221 space equals space 12.78

    left parenthesis straight b right parenthesis space Volume space of space 0.01 space MH subscript 2 SO subscript 4 space equals space 10 space mL space left parenthesis given right parenthesis
Volume space of space 0.01 space straight M space Ca left parenthesis OH right parenthesis subscript 2 space equals space 10 space mL space left parenthesis given right parenthesis
    Since two solutions have equal moles of H+ and OH- ions, therefore the two solutions get completely neutralised and the pH = 7.0

    left parenthesis straight c right parenthesis space Volume space of space 0.1 space MH subscript 2 SO subscript 4 space equals space 10 space mL left parenthesis given right square bracket
Volume space of space 0.1 space straight M space KOH space equals space 10 space mL space left parenthesis given right square bracket
straight M left parenthesis straight H to the power of plus right parenthesis space equals space fraction numerator straight M subscript 1 straight V subscript 1 left parenthesis Acid right parenthesis space minus space straight M subscript 2 straight V subscript 2 left parenthesis Base right parenthesis over denominator straight V subscript 1 space plus space straight V subscript 2 end fraction
space space space space space space space space space equals space fraction numerator 0.1 space cross times space 2 space cross times space 10 space minus space 0.1 space cross times space 10 space over denominator 10 space plus space 10 end fraction equals space fraction numerator 2 minus 1 over denominator 20 end fraction space equals 1 over 20
space space space space space space space space space space space 0.05 space equals space 5 space cross times 10 to the power of negative 2 end exponent straight M
     
    But space pH space equals space minus log space open square brackets straight H to the power of plus close square brackets space equals space minus log space left parenthesis 5 space cross times space 10 to the power of negative 2 end exponent right parenthesis
space space space space space space space space space space equals negative log space 5 space minus space log space 10 to the power of negative 2 end exponent
space space space space space space space space space space equals negative 0.6990 space plus 2 space equals space 1.30

    Question 251
    CBSEENCH11006550

    How many grammes of NaOH must be dissolved in one litre of the solution to give it a pH value of 12?

    Solution
    By definition,
    open square brackets straight H to the power of minus close square brackets space equals space 10 to the power of negative pH end exponent space equals 10 to the power of negative 12 end exponent space mol space straight L to the power of negative 1 end exponent
We space know comma space open square brackets straight H to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets space equals space straight K subscript straight w
or space space open square brackets OH to the power of minus close square brackets space equals space fraction numerator straight K subscript straight w over denominator open square brackets straight H to the power of plus close square brackets end fraction space equals space fraction numerator 1 space cross times space 10 to the power of negative 14 end exponent over denominator 10 to the power of negative 12 end exponent end fraction
space space space space space space space space space space space space space space space space space equals 1 space cross times space 10 to the power of negative 2 end exponent space mol space straight L to the power of negative 1 end exponent
    Since NaOH is a strong electrolyte, it gets completely ionised. So we have
    NaOH space plus space straight H subscript 2 straight O space space rightwards arrow space space space Na to the power of plus left parenthesis aq right parenthesis space plus space OH to the power of minus left parenthesis aq right parenthesis
therefore space space space open square brackets OH close square brackets to the power of minus space equals space open square brackets NaOH close square brackets space equals space 1 space cross times space 10 to the power of negative 2 end exponent space mol space straight L to the power of negative 1 end exponent
therefore space space space Molarity space of space NaOH space solution space equals space 1 space cross times space 10 to the power of negative 2 end exponent straight M
therefore space space space space space Molecular space mass space of space NaOH space equals space 40
therefore space space Amount space of space NaOH space present space in space one space litre
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space Molar space mass space cross times space molarity
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space 40 cross times 10 to the power of negative 2 end exponent space equals 0.4 space straight g
    Question 252
    CBSEENCH11006551

    Calculate the pH of a solution obtained by mixing 150 mL of 0.1 N - NaOH and 150 ml of 0.2 N - HCl.

    Solution
    In such problems of acid and base mixture solution, we should determine the volume of each having unit normality (or molarity).
    Now 150 ml of 0.1 space straight N space minus space NaOH
                           identical to space 150 space cross times space 0.1 space mL space of space straight N minus NaOH
identical to space 15 space mL space of space straight N minus NaOH
    150 space mL space of space 0.2 space straight N space minus space HCl
space space space space space space space space space space space space space space space space space space space space space space space space space space space identical to space 150 space cross times space 0.2 space mL space of space straight N minus HCl
space space space space space space space space space space space space space space space space space space space space space space space space space space space identical to space space space space 30 space mL space of space straight N minus HCl

space space space space space space space space space space space space space space space space space space space space space space space space
    15 space mL space of space straight N minus space NaOH  are neutralised by 15 mL of N-HCl
    HCl left unused after mixing the two solutions
                                       = (30 - 15) i.e. 15 mL of N-solution
      Total , volume of the solution after mixing
                            = 150 + 150 = 300 mL
    Now comma space space space space space straight N subscript 1 straight V subscript 1 space equals space straight N subscript 2 straight V subscript 2
or space space space space space space space space space 1 cross times 15 space equals space straight N subscript 2 space cross times space 300
therefore space space space space space straight N subscript 2 space equals space 15 over 300 space equals space 1 over 20
    Since HCl is a strong electrolyte, it is completely dissociated. 
       HCl space plus space straight H subscript 2 straight O space space rightwards harpoon over leftwards harpoon space space straight H subscript 3 straight O to the power of plus left parenthesis aq right parenthesis space plus space Cl to the power of minus left parenthesis aq right parenthesis
space space space space open square brackets straight H to the power of plus close square brackets space equals space open square brackets HCl close square brackets space equals space 1 over 20 straight N space equals space 1 over 20 straight M
We space know comma space
space space space space space space pH space equals space minus log space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space equals space minus log space open square brackets 1 over 20 close square brackets
space space or space pH space equals space log space 20 space equals space 1.3010
                 
    Question 253
    CBSEENCH11006552

    How does Arrhenius theory help in comparing the relative strengths of weak acids and weak bases?

    Solution
    The relative strength of weak acids: The relative strength of weak acids can be easily compared in terms of their dissociation constants. In a gaseous solution, the dissociation of weak acid says HA may be represented as,
    <pre>uncaught exception: <b>Http Error #404</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php line 61<br />#0 [internal function]: com_wiris_plugin_impl_HttpImpl_0(Object(com_wiris_plugin_impl_HttpImpl), NULL, 'http://www.wiri...', 'Http Error #404')
#1 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('com_wiris_plugi...', Array)
#2 [internal function]: _hx_lambda->execute('Http Error #404')
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(532): call_user_func_array(Array, Array)
#4 [internal function]: haxe_Http_5(true, Object(com_wiris_plugin_impl_HttpImpl), Object(com_wiris_plugin_impl_HttpImpl), Array, Object(haxe_io_BytesOutput), true, 'Http Error #404')
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('haxe_Http_5', Array)
#6 [internal function]: _hx_lambda->execute('Http Error #404')
#7 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(27): call_user_func_array(Array, Array)
#8 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(444): com_wiris_plugin_impl_HttpImpl->onError('Http Error #404')
#9 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(458): haxe_Http->customRequest(true, Object(haxe_io_BytesOutput), NULL, NULL)
#10 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(40): haxe_Http->request(true)
#11 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(80): com_wiris_plugin_impl_HttpImpl->request(true)
#12 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#13 {main}</pre>
    Since water used as a solvent is present in large quantity, its concentration remains practically constant.
    <pre>uncaught exception: <b>Http Error #404</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php line 61<br />#0 [internal function]: com_wiris_plugin_impl_HttpImpl_0(Object(com_wiris_plugin_impl_HttpImpl), NULL, 'http://www.wiri...', 'Http Error #404')
#1 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('com_wiris_plugi...', Array)
#2 [internal function]: _hx_lambda->execute('Http Error #404')
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(532): call_user_func_array(Array, Array)
#4 [internal function]: haxe_Http_5(true, Object(com_wiris_plugin_impl_HttpImpl), Object(com_wiris_plugin_impl_HttpImpl), Array, Object(haxe_io_BytesOutput), true, 'Http Error #404')
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('haxe_Http_5', Array)
#6 [internal function]: _hx_lambda->execute('Http Error #404')
#7 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(27): call_user_func_array(Array, Array)
#8 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(444): com_wiris_plugin_impl_HttpImpl->onError('Http Error #404')
#9 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(458): haxe_Http->customRequest(true, Object(haxe_io_BytesOutput), NULL, NULL)
#10 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(40): haxe_Http->request(true)
#11 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(80): com_wiris_plugin_impl_HttpImpl->request(true)
#12 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#13 {main}</pre>
    Ka is known as dissociation constant of acid. It is constant at a given temperature for a given acid. Higher the value of Ka, the stronger is the acid.
    <pre>uncaught exception: <b>Http Error #404</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php line 61<br />#0 [internal function]: com_wiris_plugin_impl_HttpImpl_0(Object(com_wiris_plugin_impl_HttpImpl), NULL, 'http://www.wiri...', 'Http Error #404')
#1 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('com_wiris_plugi...', Array)
#2 [internal function]: _hx_lambda->execute('Http Error #404')
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(532): call_user_func_array(Array, Array)
#4 [internal function]: haxe_Http_5(true, Object(com_wiris_plugin_impl_HttpImpl), Object(com_wiris_plugin_impl_HttpImpl), Array, Object(haxe_io_BytesOutput), true, 'Http Error #404')
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('haxe_Http_5', Array)
#6 [internal function]: _hx_lambda->execute('Http Error #404')
#7 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(27): call_user_func_array(Array, Array)
#8 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(444): com_wiris_plugin_impl_HttpImpl->onError('Http Error #404')
#9 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(458): haxe_Http->customRequest(true, Object(haxe_io_BytesOutput), NULL, NULL)
#10 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(40): haxe_Http->request(true)
#11 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(80): com_wiris_plugin_impl_HttpImpl->request(true)
#12 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#13 {main}</pre>
    or space space space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space equals space square root of straight K subscript straight a space cross times space open square brackets HA close square brackets end root
space space space open square brackets HA close square brackets space equals space concentration space of space the space weak space acid
space space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space equals concentration space of space straight H to the power of plus left parenthesis aq right parenthesis space ions
    If we have two weak acids having the same molar concentration in aqueous solution i.e. C mol L , then
    fraction numerator Strength space of space Acid space minus space 1 over denominator Strenght space of space Acid space minus space 2 end fraction space equals space fraction numerator square root of straight K subscript straight a subscript 1 end subscript cross times straight C end root over denominator straight K subscript straight a subscript 2 end subscript space cross times space straight C end fraction
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space square root of straight K subscript straight a subscript 1 end subscript over straight K subscript straight a subscript 2 end subscript end root

    Hence the relative strength of two acids having the same molar concentration in aqueous solution may be compared in terms of the square root of their dissociation constants.
    Relative strength of weak base:
    The dissociation of weak base, say BOH may be represented as,
    BOH left parenthesis aq right parenthesis space plus space straight H subscript 2 straight O left parenthesis straight l right parenthesis space space rightwards harpoon over leftwards harpoon space space space straight B to the power of plus left parenthesis aq right parenthesis space plus space OH to the power of minus left parenthesis aq right parenthesis
    According to law of chemical equilibrium
                    straight K subscript straight c space equals space fraction numerator open square brackets straight B to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets over denominator open square brackets BOH close square brackets space open square brackets straight H subscript 2 straight O close square brackets end fraction

    Since water is used as a solvent, its concentration remains practically constant.
    straight K subscript straight c space cross times space open square brackets straight H subscript 2 straight O close square brackets space equals space fraction numerator open square brackets straight B to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets over denominator open square brackets BOH close square brackets end fraction
or space space space straight K subscript straight b space equals space fraction numerator open square brackets straight B to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets over denominator open square brackets BOH close square brackets end fraction
    Kb is known as dissociation constant base. It is constant at a given temperature for a given base. Higher the value of Kb, stronger is the base.
     
    Similarly, the relative strength of the weak bases may also be compared as,
    fraction numerator Strength space of space base space minus space 1 over denominator Strength space of space base space minus 2 end fraction space equals square root of straight K subscript straight b subscript 1 end subscript over Kb subscript 2 end root
    Question 255
    CBSEENCH11006554

    Arrange the following in decreasing order of acidic strength:
    (i) HOCl (Ka = 3·0 × 10–8)
    (ii) HCN (Ka = 4·0 × 10–10)
    (iii) HNO3 (Ka = 4·5 × 10–4)
    (iv) HF (Ka = 6·7 × 10–4)

    Solution

    Greater the Ka value, stronger will be the acid.
    ∴  
    Decreasing order of acidic strength is
    HF > HNO3 > HOCl > HCN.

    Question 256
    CBSEENCH11006555

    Calculate the pH of a 0·08M solution of hypochlorous acid, HOCl. The ionisation constant of the acid is 2·5 × 10–5. Determine the percent dissociation of HOCl. 

    Solution
    Let the amount of HOCl dissociated be x mol L-1
    HOCl   +   H2O     rightwards harpoon over leftwards harpoon      H3O+  + ClO- 
    Initial conc.      
     0.08                              0          0
    At eqm.              
    008 - x                          x           x
                        
    therefore space space space straight K subscript straight a space equals space fraction numerator open square brackets straight H subscript 3 straight O to the power of plus close square brackets space open square brackets ClO to the power of minus close square brackets over denominator open square brackets HOCl close square brackets end fraction space equals space fraction numerator straight x space cross times space straight x over denominator 0.08 end fraction space equals space fraction numerator straight x squared over denominator 0.08 end fraction
space or space space space straight x squared space space equals straight K subscript straight a space cross times space 0.08 space equals space 2.15 space cross times space 10 to the power of negative 5 end exponent space cross times space 0.08
space space space space space space space space space space space space equals space 2.0 space cross times space 10 to the power of negative 6 end exponent
or space space space space straight x space equals space square root of 2.0 space cross times space 10 to the power of negative 6 end exponent end root space equals space 1.41 space cross times space 10 to the power of negative 3 end exponent
or space space space space open vertical bar straight H subscript 3 straight O to the power of plus close vertical bar space equals space 1.41 space cross times space 10 to the power of negative 3 end exponent straight M
space space space pH space equals space minus log space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space equals space minus log space left parenthesis 1.41 space cross times space 10 to the power of minus right parenthesis
space space space space space space space space equals space 2.85
    percent sign space age space dissociation space equals space fraction numerator Amount space dissociated over denominator Amount space taken end fraction cross times space 100
space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals fraction numerator 1.41 space cross times space 10 to the power of negative 3 end exponent over denominator 0.08 end fraction cross times 100 space equals space 1.76 percent sign
    Question 257
    CBSEENCH11006556

    At 298 K, calculate the pH of 0·23 M weak acid (ionisation constant = 7·3 × 10–6). 

    Solution
    For the weak acid HX in an aqueous solution,
    HX space plus space straight H subscript 2 straight O space space space rightwards harpoon over leftwards harpoon space space straight H subscript 3 straight O to the power of plus space space plus space straight X to the power of minus
    If C is the initial concentration of HX and straight alpha be its degree of dissociation, then
                            HX +  H2O     rightwards harpoon over leftwards harpoon       H3O+    +   X-
    Initial conc.          C mol L-                   0               0
    Equilibrium             straight C minus Cα                   Cα            Cα
    conc
          Applying the law of chemical equilibrium,
        straight K subscript straight alpha space equals space fraction numerator open square brackets straight H subscript 3 straight O to the power of plus close square brackets space open square brackets straight X to the power of minus close square brackets over denominator open square brackets HX close square brackets end fraction
space space space space space equals space fraction numerator Cα space cross times space Cα over denominator straight C minus Cα end fraction
space space space space space space equals space fraction numerator straight C squared straight alpha squared over denominator straight C left parenthesis 1 minus straight alpha right parenthesis end fraction
space space space space space space equals fraction numerator Cα squared over denominator 1 minus straight alpha end fraction
    or space space space straight K subscript straight alpha space equals space Cα squared space space space space space space space space space space space space open square brackets because space space 1 minus straight alpha space asymptotically equal to space 1 close square brackets
or space space space space straight alpha space equals space square root of straight K subscript straight alpha over straight C end root
space space space space space space space space space equals square root of fraction numerator 7.3 space cross times space 10 to the power of negative 6 end exponent over denominator 0.23 end fraction end root
space space space space space space space space equals square root of 31.74 space cross times space 10 to the power of negative 6 end exponent end root
space space space space space space space space equals space 5.63 space cross times space 10 to the power of negative 3 end exponent

    open square brackets straight H subscript 3 straight O to the power of plus close square brackets space equals space Cα space equals space 0.23 space cross times space 5.63 space cross times space 10 to the power of negative 3 end exponent
space space space space space space space space space space space space equals space 1.295 space cross times space 10 to the power of negative 3 end exponent straight M
    We space know comma space
space space space pH space equals space minus log space open square brackets straight H subscript 3 straight O to the power of plus close square brackets
space space space space space space space space equals space minus log space left parenthesis 1.295 space cross times 10 to the power of negative 3 end exponent right parenthesis
space space space space space space space space equals negative left square bracket log space 1.295 space minus space 3 space log space 10 right parenthesis space space space space
space space space space space space space space equals negative left square bracket 0.1122 minus space 3 right square bracket space space space left square bracket because space log space 10 space equals space 1 right square bracket
space space space space space space space space equals negative 0.1122 space plus space 3
space space space space space space space space equals 2.8878 space almost equal to space 2.89 space space space space space

                      
                 
      
    Question 261
    CBSEENCH11006560

    The pH of 0·005M codeine (C18H21NO3) solution is 9·95. Calculate its ionization constant and pKb.

    Solution

    We know,
       negative log space open square brackets straight H to the power of plus close square brackets space equals space pH
or space space log space open square brackets straight H to the power of plus close square brackets space equals negative pH space equals space minus 9.95 space equals space minus 9 minus 0.95 space minus 1
space space space space space space space space space space space space space space space space space equals 10 with bar on top.05
or space space space space space open square brackets straight H to the power of plus close square brackets space equals space antilog space left parenthesis 10 with bar on top.05 right parenthesis
space space space space space space space space space space space space space space space equals 1.12 space cross times space 10 to the power of negative 10 end exponent straight M
Also comma space space straight K subscript straight w space equals open square brackets straight H to the power of plus close square brackets space open square brackets straight O with bar on top straight H close square brackets
or space space space space open square brackets OH to the power of minus close square brackets space equals space fraction numerator straight K subscript straight w over denominator open square brackets straight H to the power of plus close square brackets end fraction
space space space space space space space space space space space space space space space space equals fraction numerator 10 to the power of negative 14 end exponent over denominator 1.12 space cross times 10 to the power of 10 end fraction
                     equals space 8.93 space cross times space 10 to the power of negative 5 end exponent straight M
    The concentration of codeine ion is also same as that of hydroxyl ion. The concentration of the ions is very small and hence the concentration of undissociated base can be taken as equal to 0·005 M.
    Thus comma space space space straight K subscript straight b space equals space fraction numerator open square brackets straight M to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets over denominator open square brackets MOH close square brackets end fraction space equals fraction numerator left parenthesis 8.93 space cross times space 10 to the power of negative 5 end exponent right parenthesis squared over denominator 0.005 end fraction
space space space space space space space space space space space space space space equals space 1.6 space cross times space 10 to the power of negative 6 end exponent
pK subscript straight b space equals space minus log space straight K subscript straight b space equals space minus log space left parenthesis 1.6 space cross times space 10 to the power of negative 6 end exponent right parenthesis space equals space 5.8

    Question 263
    CBSEENCH11006562

    The ionisation constant of dimethylamine is 5·4 × 10–4. Calculate its degree of ionisation in its 0-02M solution. What percentage of dimethylamine is ionised if the solution is also 0·1M in NaOH?

    Solution

    We know, 
    straight alpha space equals square root of straight K subscript straight b over straight C end root space equals space square root of left parenthesis 5.4 space cross times space 10 to the power of negative 4 end exponent divided by left parenthesis 2 space cross times space 10 to the power of negative 2 end exponent right parenthesis end root
space space equals space 0.164
    Suppose x is the amount of dimethylamine dissociated in the presence of 0.1 M NaOH.
     (CH3)2NH   +   H2O rightwards harpoon over leftwards harpoon  (CH3)2NH+OH-  + OH-
    Initial conc      
    0.02 M                               0                   0
    After
    dissociation      
    0.02 - x                              x             0.1 + x
     = 0.02                                              = 0.1
        straight K subscript straight b space equals space fraction numerator open square brackets left parenthesis CH subscript 3 right parenthesis subscript 2 NH to the power of plus OH to the power of minus close square brackets space open square brackets OH to the power of minus close square brackets over denominator open square brackets left parenthesis CH subscript 3 right parenthesis subscript 2 NH close square brackets end fraction space equals space fraction numerator straight x left parenthesis 0.1 right parenthesis over denominator 0.02 end fraction
space fraction numerator straight x over denominator 0.02 end fraction space equals space fraction numerator straight K subscript straight b over denominator 0.1 end fraction space equals space fraction numerator 5.4 space cross times space 10 to the power of negative 4 end exponent over denominator 0.1 end fraction space equals space 5.4 space cross times space 10 to the power of negative 3 end exponent
straight i. straight e. space straight alpha space equals space fraction numerator straight x over denominator 0.02 end fraction space equals space 5.4 space cross times space 10 to the power of negative 3 end exponent
therefore space percent sign space age space of space ionisation space of space dimethylamine space equals space 0.54

    Question 264
    CBSEENCH11006563

    The ionisation constant of phenol is 1·0 × 10–10. What is the concentration of phenolate ion in a 0·05W solution of phenol? What be its degree of ionisation if the solution is also 0·01M in sodium phenolate?

    Solution
    (a) Calculation of concentration of phenolate ion:
    We know,  <pre>uncaught exception: <b>Http Error #404</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php line 61<br />#0 [internal function]: com_wiris_plugin_impl_HttpImpl_0(Object(com_wiris_plugin_impl_HttpImpl), NULL, 'http://www.wiri...', 'Http Error #404')
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    therefore space space space space straight alpha space equals space square root of fraction numerator 1.0 space cross times space 10 to the power of negative 10 end exponent over denominator 0.05 end fraction end root space equals space 0.44 space cross times space 10 to the power of negative 4 end exponent
therefore space space space Concentration space of space phenolate space ion space open square brackets straight C subscript 6 straight H subscript 5 straight O to the power of minus close square brackets
space space space equals space straight C space cross times space straight alpha space equals space 0.05 space cross times space 0.44 space cross times space 10 to the power of negative 4 end exponent space equals space 2.2 space cross times space 10 to the power of negative 6 end exponent
    (b) Calculation of degree of ionisation in the presence of sodium phenolate:
    stack straight C subscript 6 straight H subscript 5 ONa with stack Sodium space phenolate with left parenthesis 0.01 space straight M right parenthesis below below space space space space space rightwards arrow space space space space space stack straight C subscript 6 straight H subscript 5 straight O to the power of minus with left parenthesis 0.01 space straight M right parenthesis below
space space space space space space space space stack straight C subscript 6 straight H subscript 5 OH with straight C minus straight x below space space space space space space space leftwards harpoon over rightwards harpoon space space space space space space stack space straight H to the power of plus with straight x below space space plus space stack straight C subscript 6 straight H subscript 5 straight O to the power of minus with straight x below space space
    Now space open square brackets straight C subscript 6 straight H subscript 5 straight O to the power of minus close square brackets space equals space left parenthesis 0.01 plus space straight x right parenthesis space and space open square brackets straight H to the power of plus close square brackets space equals space straight x
open square brackets straight C subscript 6 straight H subscript 5 OH close square brackets space equals space straight C minus straight x space equals space left parenthesis 0.05 space minus straight x right parenthesis
Now space space space straight K subscript straight a space equals space fraction numerator open square brackets straight H to the power of plus close square brackets space open square brackets straight C subscript 6 straight H subscript 5 straight O to the power of minus close square brackets over denominator open square brackets straight C subscript 6 straight H subscript 5 OH close square brackets end fraction space equals space fraction numerator straight x space cross times space left parenthesis 0.01 space plus straight x right parenthesis over denominator 0.05 minus space straight x end fraction
Since space straight x space is space very space small comma space therefore
space space straight K subscript straight a space equals space fraction numerator 0.01 space cross times space straight x over denominator 0.05 end fraction
or space space space space straight x space equals space fraction numerator straight K subscript straight a space cross times space 0.05 over denominator 0.01 end fraction space equals space fraction numerator 1.0 space cross times space 10 to the power of negative 10 end exponent space cross times space 0.05 over denominator 0.01 end fraction
space space space space space space space space space space equals 5 space cross times space 10 to the power of negative 10 end exponent straight M
    therefore space space space Degree space of space ionisation
space space space straight alpha space equals space straight x over straight C space equals space fraction numerator 5 space cross times space 10 to the power of negative 10 end exponent over denominator 0.05 end fraction space equals space 1 space cross times space 10 to the power of negative 8 end exponent
    Question 267
    CBSEENCH11006566

    At 298 K, calculate the pH of 0.200 M solution of methylamine, CH3NH2(ionisation constant = 4·4×105).

    Solution
    In aqueous solution.
    CH subscript 3 NH subscript 2 space plus space straight H subscript 2 straight O space space rightwards harpoon over leftwards harpoon space space space CH subscript 3 NH subscript 3 superscript plus space plus space OH to the power of minus
    If C is the initial concentration and a is the degree of dissociation, then,
    space space space space space space space space space space space space space space space CH subscript 3 NH subscript 2 space space space space plus space space straight H subscript 2 straight O space space space space rightwards harpoon over leftwards harpoon space space space space space space CH subscript 3 NH subscript 3 superscript plus space space space space plus space space space space space OH to the power of minus
Initial space conc space space space space space space space straight C space mol space straight L to the power of negative 1 end exponent space space space space space space space space space space space space space space space space space space space space space space space space 0 space space space space space space space space space space space space space space space space space space 0 space space space space space space space space
Equilibrium space space space space space space space space straight C minus Cα space space space space space space space space space space space space space space space space space space space space space space space space space space space Cα space space space space space space space space space space space space space space space space Cα
    straight K subscript straight b space equals space fraction numerator open square brackets CH subscript 3 NH subscript 3 superscript plus close square brackets space open square brackets OH to the power of minus close square brackets over denominator open square brackets CH subscript 3 NH subscript 2 close square brackets end fraction
space space space space space equals space fraction numerator Cα space cross times space Cα over denominator straight C space minus space Cα end fraction space equals space fraction numerator straight C squared straight alpha squared over denominator straight C left parenthesis 1 minus straight alpha right parenthesis end fraction space equals space fraction numerator Cα squared over denominator 1 minus straight alpha end fraction
or space space space straight K subscript straight b space end subscript space equals space Cα squared space space space space space space space space space space space space space open square brackets because space 1 minus straight alpha space equals space 1 close square brackets
or space space space space straight alpha space equals space square root of straight K subscript straight b over straight C end root
space space space space space space space space space space space equals square root of fraction numerator 4.4 space cross times 10 to the power of negative 5 end exponent over denominator 0.200 end fraction end root
space space space space space space space space space space space equals 1.48 space cross times 10 to the power of negative 2 end exponent

    therefore space space open square brackets OH to the power of minus close square brackets space equals space straight C space cross times space straight alpha
space space space space space space space space space space space space space space space equals 0.200 space cross times space 1.48 space cross times space 10 to the power of negative 2 end exponent
space space space space space space space space space space space space space space space equals 2.96 space cross times 10 to the power of negative 3 end exponent straight M
We space know comma space space space space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets space equals space straight K subscript straight w
or space space space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space equals space fraction numerator straight K subscript straight w over denominator open square brackets OH to the power of minus close square brackets end fraction space equals space fraction numerator 1 space cross times space 10 to the power of negative 14 end exponent over denominator 2.96 space cross times 10 to the power of negative 3 end exponent end fraction
space space space space space space space space space space space space space space space space space equals space 3.378 space cross times space 10 to the power of negative 12 end exponent space space space space space space space space space space space space space space space space space space space
    Also comma space
space space space pH space equals negative log space open square brackets straight H subscript 3 straight O to the power of plus close square brackets
space space space space space space space space equals negative log space left parenthesis 3.378 space cross times space 10 to the power of negative 12 end exponent right parenthesis
space space space space space space space space equals space minus log space left square bracket 3.378 space plus space log space 10 to the power of negative 12 end exponent right square bracket
space space space space space space space space equals negative open square brackets log space 3.378 space minus space 12 space log space 10 close square brackets
space space space space space space space space equals negative left square bracket 0.5287 space minus space 12 right square bracket
space space space space space space space space equals space 11.4712 space asymptotically equal to space 11.47
    Question 269
    CBSEENCH11006568

    The ionisation constant of propanoic acid is 1·32 × 10–5. Calculate the degree of ionisation of the acid in its 0·05M solution and also it's pH. What will be its degree of ionisation if the solution is 0·01M in HCl also? 

    Solution
    Applying the Ostwald dilution law,
    straight alpha space equals square root of straight K subscript straight a over straight C end root space equals square root of fraction numerator 1.32 space cross times space 10 to the power of negative 5 end exponent over denominator 0.05 end fraction end root space equals space 1.62 space cross times space 10 to the power of negative 2 end exponent
Also
space space open square brackets straight H to the power of plus close square brackets space equals space square root of straight K subscript straight a space cross times space straight C end root space equals space square root of 1.32 space cross times space 10 to the power of negative 5 end exponent space cross times space 0.05 end root
space space space space space space space space equals space 8.124 space cross times space 10 to the power of negative 4 end exponent
therefore space space space pH space equals space minus log space open square brackets straight H to the power of plus close square brackets space equals space minus log left parenthesis 8.124 space cross times space 10 to the power of negative 4 end exponent right parenthesis
space space space space space space space space space space space equals negative left parenthesis log space 8.124 space minus space 4 space log space 10 right parenthesis
space space space space space space space space space space space equals left parenthesis 4 minus log space 8.124 right parenthesis space equals space left parenthesis 4 minus 0.909 right parenthesis space equals space 3.09
    Calculation of a for propanoic acid in (0·01M )HCl solution:
    space CH subscript 3 CH subscript 2 COOH space space rightwards harpoon over leftwards harpoon space space CH subscript 3 CH subscript 2 COO to the power of minus space plus space straight H to the power of plus
    In the presence of HCl, the ionisation of CH3CH3COOH will decrease (common ion effect). If C is the initial concentration of acid and x is the amount dissociated at equilibrium, then
    open square brackets CH subscript 3 CH subscript 2 COOH close square brackets space equals space straight C minus straight x semicolon space space space open square brackets CH subscript 3 CH subscript 2 COO to the power of minus close square brackets space equals straight x semicolon
space space space open square brackets straight H to the power of plus close square brackets space equals space 0.01 space plus space straight x
therefore space space space straight K subscript straight a space equals space fraction numerator open square brackets CH subscript 3 CH subscript 2 COO to the power of minus close square brackets space open square brackets straight H to the power of plus close square brackets over denominator open square brackets CH subscript 3 CH subscript 2 COOH close square brackets end fraction
space space space space space space space space space space space space equals fraction numerator left parenthesis straight x right parenthesis space cross times space left parenthesis 0.01 space plus space straight x right parenthesis over denominator straight C minus straight x end fraction space equals space fraction numerator straight x left parenthesis 0.01 right parenthesis over denominator straight C end fraction
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space open square brackets because space straight x space is space very minus very space small close square brackets
space space space space space space space or space space straight x over straight C space equals space fraction numerator straight K subscript straight a over denominator 0.01 end fraction space equals space fraction numerator 1.32 space cross times space 10 to the power of negative 3 end exponent over denominator 10 to the power of negative 2 end exponent end fraction
or space space space space space straight alpha space equals space straight x over straight C space equals space 1.32 space cross times space 10 to the power of negative 3 end exponent

    Question 271
    CBSEENCH11006570

    Explain common in effect.

    Solution
    Common ion effect defined as the suppression of the degree of dissociation of weak electrolyte (weak acid or weak base) by the addition of strong electrolyte containing common ion.Let us consider the ionisation of weak base.
    NH subscript 4 OH left parenthesis aq right parenthesis space space rightwards harpoon over leftwards harpoon space space space NH subscript 4 superscript plus left parenthesis aq right parenthesis space plus space OH to the power of minus left parenthesis aq right parenthesis
    If solid NH4Cl is added to the solution, the concentration of NH4+ ions increases. According to Le-Chatelier’s principle, the equilibrium shifts to the left. As a result, the concentration of O ion decreases and the weak base NH4OH becomes even weaker in the presence of its salt.

    This phenomenon is called common ion effect. 
    Question 272
    CBSEENCH11006571

    Discuss the salt hydrolysis in the following cases:
    (i) Salts of strong acid and strong base
    (ii) Salts of strong acid and weak base
    (iii) Salts of weak acid and strong base
    (iv) Salts of weak acid and weak base.

    Solution

    (i) Salts of strong acid and strong base:
    When a salt of the strong acid and a strong base (say NaCl) is dissolved in water, the resulting solution is neutral having pH equal to 7. The hydrolysis of the salt can be represented as:
    NaCl space plus space aq space rightwards harpoon over leftwards harpoon space space space space Na to the power of plus space plus space Cl to the power of minus
space space space space space straight H subscript 2 straight O space space rightwards harpoon over leftwards harpoon space space space straight H to the power of plus space plus space OH to the power of minus
The space overall space process space will space be
space space space space space NaCl space plus space straight H subscript 2 straight O space space rightwards harpoon over leftwards harpoon space space space Na to the power of plus space plus space Cl to the power of minus space plus space straight H to the power of plus space plus space OH to the power of minus

    i.e. there is the only dissociation of sodium chloride and no hydrolysis.
    (ii) Salts of strong acid and weak base:
    When a salt of the strong acid and a weak base is dissolved in water, it gives an acidic solution having pH value less than 7. For example hydrolysis of NH4Cl can be represented as:
       NH subscript 4 Cl space plus space straight H subscript 2 straight O space space rightwards harpoon over leftwards harpoon space space space NH subscript 4 OH space plus space HCl
    or space space space NH subscript 4 superscript plus space plus space Cl to the power of minus space plus space straight H subscript 2 straight O space rightwards harpoon over leftwards harpoon space space NH subscript 4 OH space plus space straight H to the power of plus space plus space Cl to the power of minus
    The overall reaction will be
    NH subscript 4 superscript plus space plus space straight H subscript 2 straight O space space rightwards harpoon over leftwards harpoon space space space space NH subscript 4 OH space plus space straight H to the power of plus
    i.e. it is a cationic hydrolysis.
    (iii) Salts of weak acid and strong base:
    When a salt of weak acid and a strong base is dissolved in water, it gives a basic solution having pH greater than 7. For example hydrolysis of sodium acetate can be represented as:
    space CH subscript 3 COONa space plus space straight H subscript 2 straight O space rightwards harpoon over leftwards harpoon space space CH subscript 3 COOH space plus space NaOH
space or space space space CH subscript 3 COO to the power of minus space plus space Na to the power of plus space plus space straight H subscript 2 straight O space rightwards harpoon over leftwards harpoon space space CH subscript 3 COOH space plus space Na to the power of plus space plus space OH to the power of minus
       The overall reaction will be
     CH subscript 3 COO to the power of minus space plus space straight H subscript 2 straight O space space rightwards harpoon over leftwards harpoon space space space CH subscript 3 COIOH space plus space OH to the power of minus
    i.e. it is an anionic hydrolysis.

    (iv) Salts of weak acid and weak base:
    When a salt of weak acid and a weak base is dissolved in water, it forms an almost neutral aqueous solution having value almost equal to 7. For example, hydrolysis of ammonium acetate can be represented as:
    CH subscript 3 COONH subscript 4 space plus space straight H subscript 2 straight O space space rightwards harpoon over leftwards harpoon space space CH subscript 3 COOH space plus space NH subscript 4 OH
    The overall reaction will be
    CH subscript 3 COO to the power of minus NH subscript 4 superscript plus space plus space straight H subscript 2 straight O space space rightwards harpoon over leftwards harpoon space space space CH subscript 3 COOH space plus space NH subscript 4 OH
    i.e. it involves both anionic as well as cationic hydrolysis.

    Question 273
    CBSEENCH11006572

    predict if the solutions of the following salts are neutral, acidic or basic : NaCl, KBr, NaCN, NH4NO3, NaNO2 and KF. 

    Solution

    (i) NH4NO3 solution is acidic, as it is a salt of the strong acid and a weak base, having pH < 7.
    (ii) NaCN, NaNO2, KF solutions are basic, as they are salts of a strong base and a weak acid, having pH > 7.
    (iii) NaCl, KBr solutions are neutral, as they are the salts of a strong acid and strong base, having pH = 7.

    Question 274
    CBSEENCH11006573

    Explain the following terms:
    (i) Hydrolysis constant
    (ii) Degree of hydrolysis.

    Solution

    (i) Hydrolysis constant:
    Hydrolysis of a salt (BA) may be represented as
                          BA space plus straight H subscript 2 straight O space rightwards harpoon over leftwards harpoon space space space HA space plus space BOH
    Applying the law of chemical equilibrium, we get, 
                        space straight K space equals space fraction numerator open square brackets HA close square brackets space open square brackets BOH close square brackets over denominator space open square brackets BA close square brackets space open square brackets straight H subscript 2 straight O close square brackets end fraction
    Since water is present in very large excess in aqueous solution, its concentration open square brackets straight H subscript 2 straight O close square brackets may be regarded as constant.
                                    straight K space cross times space open square brackets straight H subscript 2 straight O close square brackets space equals space fraction numerator open square brackets HA close square brackets space open square brackets BOH close square brackets over denominator open square brackets BA close square brackets end fraction
or space space space space space space space space space straight K subscript straight h space equals space fraction numerator open square brackets HA close square brackets space open square brackets BOH close square brackets over denominator open square brackets BA close square brackets end fraction
where space straight K subscript straight h space equals space straight K space cross times space open square brackets straight H subscript 2 straight O close square brackets space is space another space constant space called space the space hydrolysis space constant. space
    Since [HA] and [BOH] represent the molar concentration of the free acid and the free base produced and [BA] represents the molar concentration of the unhydrolyzed salt, the expression for the hydrolysis constant may be written as,
    straight K subscript straight h space equals space fraction numerator open square brackets Free space acid close square brackets space space open square brackets Free space base close square brackets over denominator left square bracket Unhydrolysed space salt right square bracket end fraction
    (ii) The degree of hydrolysis: The degree of hydrolysis (α) of a salt is defined as the fraction (or percentage) of the total salt which is hydrolysed. For example, if in a solution of aniline hydrochloride, 90% of the salt is hydrolyzed into aniline and hydrochloric acid, the degree of hydrolysis is 0·90 Or may be expressed as percentage i.e. 90%.

    Question 275
    CBSEENCH11006574

    Derive the relation,straight K subscript straight h space equals space straight K subscript straight w over straight K subscript straight b space in the case of hydrolysis of salts of strong acids and weak acids.

    Solution
    Let the salt of strong acid and weak base (such as CuSO4) be X Y and the hydrolysis reaction represented as:
           straight X to the power of plus space plus space straight H subscript 2 straight O space rightwards harpoon over leftwards harpoon space space space space stack XOH space plus space straight H to the power of plus with left square bracket Cationic space hydrolysis right square bracket below
Applying space the space law space of space chemical space equilibrium comma
space space space space straight K subscript straight b space equals space fraction numerator open square brackets XOH close square brackets space open square brackets straight H to the power of plus close square brackets over denominator open square brackets straight X to the power of plus close square brackets end fraction
space space space space space space space space space equals fraction numerator open square brackets Free space base close square brackets space open square brackets Free space acid close square brackets over denominator open square brackets Unhydrolysed space salt close square brackets end fraction space space space space space space... left parenthesis 1 right parenthesis
    [H2O] remains constants as it is taken in large excess. Following equilibrium also occurs:
            space space space space space space space space space space space space space space XOH space space space rightwards harpoon over leftwards harpoon space space space space straight X to the power of plus space plus space OH to the power of minus
space space space space space space space space space space space space space space straight H subscript 2 straight O space space rightwards harpoon over leftwards harpoon space space space straight H to the power of plus space plus space OH to the power of minus
By space the space law space of space chemical space equilibrium comma
space space space space space space space space straight K subscript straight b space equals space fraction numerator open square brackets straight X to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets over denominator open square brackets XOH close square brackets end fraction space space space space space space space space space space... left parenthesis 2 right parenthesis
and space space space straight K subscript straight w space space equals space open square brackets straight H to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets space space space space space space space space space space space... left parenthesis 3 right parenthesis
Dividing space left parenthesis 3 right parenthesis space by space left parenthesis 2 right parenthesis comma
space space space straight K subscript straight w over straight K subscript straight b space space equals space fraction numerator open square brackets straight H to the power of plus close square brackets space open square brackets XOH close square brackets over denominator open square brackets straight X to the power of plus close square brackets end fraction space space space space space space space space space space... left parenthesis 4 right parenthesis space space space space space
    Substituting the values from equation (1) in equation (4),
          straight K subscript straight h space equals space straight K subscript straight w over straight K subscript straight b
    Question 276
    CBSEENCH11006575

    Show that for an aqueous solution of a salt of weak base and strong acid straight alpha space equals space square root of straight K subscript straight w over straight K subscript straight b. straight c end subscript end root where straight alpha is the degree of hydrolysis. 

    Solution
    Let the salt of weak base and strong acid be XY and hydrolysis reaction represented as:
    straight X to the power of plus space plus space straight H subscript 2 straight O space space space rightwards harpoon over leftwards harpoon space space space space stack XOH space plus space space straight H to the power of plus with left square bracket Cationic space hydrolysis right square bracket below
    Let c be the initial concentration of the salt and a be the degree of hydrolysis. At equilibrium, the concentration of various species is represented as:
                              X +   H2O        rightwards harpoon over leftwards harpoon       XOH   +     H+
    Initial conc.                     c                        0              0
    Equilibrium
    conc.                            straight c left parenthesis 1 minus straight alpha right parenthesis               cα             cα
                       straight K subscript straight h space plus space fraction numerator cα space cross times space cα over denominator straight c left parenthesis 1 minus straight alpha right parenthesis end fraction space equals space fraction numerator cα squared over denominator left parenthesis 1 minus straight alpha right parenthesis end fraction
    Since straight alpha is very small as compared to unity. 
       therefore space space space space space space space space 1 space minus space straight alpha space equals space space 1
therefore space space space space space space space space space space space space straight K subscript straight h space equals space cα squared
or space space space space space space space space space space space space space space straight alpha squared space equals space straight K subscript straight h over straight c
or space space space space space space space space space space space space space space straight alpha space equals space square root of straight K subscript straight h over straight c end root
But space space space straight K subscript straight h space space equals space straight K subscript straight w over straight K subscript straight b
therefore space space space space space space space space space space straight alpha space equals space square root of fraction numerator straight K subscript straight w over denominator straight K subscript straight b space cross times space straight c end fraction end root space space space
    Question 277
    CBSEENCH11006576

    Derive an expression for the degree of hydrolysis of NH4Cl.

    Solution
    Hydrolysis of NH4Cl can be represented as
     NH subscript 4 superscript plus   +   H2O    rightwards harpoon over leftwards harpoon     NH4OH    +       H+
    Initial conc.                    
       c                            0                      0

    Equilibrium conc .
      straight c left parenthesis 1 minus straight alpha right parenthesis                  cα                   cα
                             straight K subscript straight h space equals space fraction numerator cα space cross times space cα over denominator straight c left parenthesis 1 minus straight alpha right parenthesis end fraction space equals space fraction numerator cα squared over denominator 1 minus straight alpha end fraction
    Since straight alpha is very small as compared to unity,

          therefore space space space space space 1 minus straight alpha space equals space 1
space space space space space space space space straight K subscript straight b space space equals space cα squared
or space space space space space space straight alpha squared space equals space straight K subscript straight h over straight c
or space space space space space space space straight alpha space equals space square root of straight K subscript straight h over straight K subscript straight b end root
But space space space straight K subscript straight h space equals space straight K subscript straight w over straight K subscript straight b
therefore space space space space space straight alpha space equals space square root of fraction numerator straight K subscript straight w over denominator straight K subscript straight b space cross times space straight c end fraction end root  

    Question 278
    CBSEENCH11006577

    Show that for an aqueous solution of a salt of weak base and strong acid,

    pH space equals space minus log space square root of straight K subscript wc over straight K subscript straight b end root.

    Solution

    Let the salt of strong acid and weak base be XY and hydrolysis reaction be represented as:
    straight X to the power of plus space plus space straight H subscript 2 straight O space space space rightwards harpoon over leftwards harpoon space space space space space stack XOH space plus space straight H to the power of plus with open square brackets Cationic space hydrolysis close square brackets below
    Let c be the initial concentration of the salt and α be the degree of hydrolysis. At equilibrium, the concentration of various species is represented as:
      X+    +      H2O       rightwards harpoon over leftwards harpoon    XOH      +     H+
    Initial conc.
      c                 c                0                  0
    Equilibrium conc.            
            straight c left parenthesis 1 minus straight alpha right parenthesis                   cα               cα
                             straight K subscript straight h space equals space fraction numerator cα space cross times space cα over denominator straight c left parenthesis 1 minus straight alpha right parenthesis end fraction space equals space fraction numerator cα squared over denominator left parenthesis 1 minus straight alpha right parenthesis end fraction
    Since straight alpha is very small as compared to unity, 


    therefore space space space space 1 minus straight alpha space equals space 1 space
therefore space space space space space space space space space straight K subscript straight h space equals space cα squared
or space space space space space space space straight alpha squared space equals space straight K subscript straight h over straight c
or space space space space space space space space straight alpha space equals space square root of straight K subscript straight h over straight c end root space
But space space space space space straight K subscript straight h space space equals space straight K subscript straight w over straight K subscript straight b
therefore space space space space space space space space straight alpha space equals space square root of fraction numerator straight K subscript straight w over denominator straight K subscript straight b straight c end fraction end root space space
    straight i. straight e. space space space open square brackets straight H to the power of plus close square brackets space equals space cα
Substituting space the space value space of space straight alpha comma
space space space space space space space space open square brackets straight H to the power of plus close square brackets space equals space straight c square root of fraction numerator straight K subscript straight w over denominator straight K subscript straight b cross times straight c end fraction end root space equals space square root of fraction numerator straight K subscript straight w straight c over denominator straight K subscript straight b end fraction end root
But space pH space equals negative log space open square brackets straight H to the power of plus close square brackets
space space space space space space space space space space equals space minus log space square root of fraction numerator straight K subscript straight w straight c over denominator straight K subscript straight b end fraction end root
space space space space space space space space space space equals negative log space open parentheses fraction numerator straight K subscript straight w straight c over denominator straight K subscript straight b end fraction close parentheses to the power of 1 divided by 2 end exponent
or space pH space equals space minus 1 half open square brackets log space straight K subscript straight w space minus space log space straight K subscript straight b space plus space log space straight c close square brackets
     

    Question 279
    CBSEENCH11006578

    Derive the relations:
    straight K subscript straight h space equals space straight K subscript straight w over straight K subscript straight a
    for a solution of a salt of weak acid and strong base.

    Solution
    Consider the hydrolysis of a simple salt of a weak acid with a strong base i.e. BA. The hydrolysis of BA may be represented as:
    space space space space space space space space space BA with Salt below space plus space straight H subscript 2 straight O space space space leftwards harpoon over rightwards harpoon space space space space space BOH with Strong below space space plus space HA
or space space space space space straight B to the power of plus space plus straight A to the power of minus space plus space straight H subscript 2 straight O space space leftwards harpoon over rightwards harpoon space space space straight B to the power of plus space plus space OH to the power of minus space plus space HA
space space space space space Cancelling space the space common space ion comma
space space space space space space space space space straight A to the power of minus space plus space straight H subscript 2 straight O space space leftwards harpoon over rightwards harpoon space space space space stack space OH to the power of minus space plus space HA with left square bracket Anionic space hyrolysis right square bracket below
    The hydrolysis constant Kh is given by
                                  straight K subscript straight h space equals space fraction numerator open square brackets OH to the power of minus close square brackets space open square brackets OH close square brackets over denominator open square brackets straight A to the power of minus close square brackets end fraction space space space space space space space... left parenthesis 1 right parenthesis
    For the weak acid HA, the dissociation equilibrium is
                                     HA space rightwards harpoon over leftwards harpoon space space space straight H to the power of plus space plus space straight A to the power of minus
    therefore space space space space space space space straight K subscript straight a space equals space fraction numerator open square brackets straight H to the power of plus close square brackets space open square brackets straight H to the power of minus close square brackets over denominator open square brackets HA close square brackets end fraction space space space space space... left parenthesis 2 right parenthesis
where space straight K subscript straight a space is space the space dissociation space constant space of space HA.
Also space ionic space product space of space water space straight K subscript straight w space is space given space by
space space space space space straight K subscript straight w space equals space open square brackets straight H to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets space space space space space space space space space space space space space... left parenthesis 3 right parenthesis
Dividing space left parenthesis 3 right parenthesis space by space left parenthesis 2 right parenthesis comma space we space get comma space
space
              straight K subscript straight w over straight K subscript straight a space equals space fraction numerator open square brackets OH to the power of minus close square brackets open square brackets HA close square brackets over denominator open square brackets straight A to the power of minus close square brackets end fraction space equals space straight K subscript straight h
    therefore space space space space space space straight K subscript straight h space equals space straight K subscript straight w over straight K subscript straight a
It space is space clear space from space equation space left parenthesis 4 right parenthesis comma space that
space space space space space space straight K subscript straight h space space proportional to space space space 1 over straight K subscript straight a
    i.e. Hydrolysis constant is inversely proportional to the dissociation constant Ka of the weak acid. Weaker the acid, the greater is the hydrolysis constant of the salt.

     
    Question 280
    CBSEENCH11006579

    Derive the relations:
    straight alpha space equals space square root of fraction numerator straight K subscript straight w over denominator straight K subscript straight a space cross times space straight c end fraction end root

    Solution
    Derivate space of space straight alpha space equals space square root of fraction numerator straight K subscript straight w over denominator straight K subscript straight a space cross times space straight c end fraction end root
    The hydrolysis of the salt (BA) may be represented as:
    straight A to the power of minus space plus space straight H subscript 2 straight O space space space space rightwards harpoon over leftwards harpoon space space space space space space OH to the power of minus space plus space HA
    Let c be the initial concentration of the salt and a be the degree of hydrolysis. At equilibrium, the concentration of various species can be represented as:
                                    straight A to the power of minus space plus space straight H subscript 2 straight O space space space rightwards harpoon over leftwards harpoon space space space space OH to the power of minus space plus space space HA
    Let c be the initial concentration of the salt and a be the degree of hydrolysis. At equilibrium, the concentration of various species can be represented as:
                                    A-  +  H2O        rightwards harpoon over leftwards harpoon     OH-     +    HA
    Initial conc.                c                                0                0
    Equilibrium conc.       straight c left parenthesis 1 minus straight alpha right parenthesis                        cα            cα
    therefore space space space space space straight K subscript straight h space equals space fraction numerator cα space cross times space cα over denominator straight c left parenthesis 1 minus straight alpha right parenthesis end fraction space equals fraction numerator cα squared over denominator 1 minus straight alpha end fraction
therefore space space space space space straight K subscript straight h space equals space fraction numerator cα squared over denominator 1 minus straight alpha end fraction space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
    Since straight alpha is very small as compared to unity,
     1 minus straight alpha space space almost equal to space 1
space space space straight K subscript straight h space space equals space ca squared
or space space space straight alpha squared space equals space straight K subscript straight h over straight c
or space space space space straight alpha space equals space square root of straight K subscript straight h over straight c end root space straight i. straight e. space space straight alpha space space space straight alpha square root of 1 over straight c end root
But space space space straight K subscript straight h space equals space straight K subscript straight w over straight K subscript straight a
therefore space space space space straight alpha space equals space square root of fraction numerator straight K subscript straight w over denominator straight K subscript straight a straight c end fraction end root space space space space space space... left parenthesis 2 right parenthesis
    From equation (2), it is clear that smaller the value of Ka (i.e. weaker the acid), the greater will be the value of a. As Kw increases with temperature, the degree of hydrolysis also increases with the increase in temperature.

                                         
    Question 281
    CBSEENCH11006580

    Derive the relations:
    pH space equals space minus log space square root of fraction numerator straight K subscript straight w. space straight K subscript straight a over denominator straight c end fraction end root
    for a solution of a salt of weak acid and strong base.


    Solution
    Derivative space of space pH space equals space minus log space square root of fraction numerator straight K subscript straight w space. space straight K subscript straight a over denominator straight c end fraction end root
    Hydrolysis of the salt, in the present case is
                           A-  +   H2O              OH-  +   HA
    Initial conc.       c                             0            0
    Equilibrium       straight c left parenthesis 1 minus straight alpha right parenthesis                   cα          cα
    conc. 
    straight i. straight e. space space space space space open square brackets OH close square brackets to the power of minus space equals space cα
But space open square brackets straight H to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets space equals space straight K subscript straight w
therefore space space space space space space open square brackets straight H to the power of plus close square brackets space equals space fraction numerator straight K subscript straight w over denominator open square brackets OH to the power of minus close square brackets end fraction
therefore space space space space space open square brackets straight H to the power of plus close square brackets space equals space straight K subscript straight w over cα
    But space space space space straight alpha space equals space square root of fraction numerator straight K subscript straight w over denominator straight K subscript straight a straight c end fraction end root
therefore space space space space space space open square brackets straight H to the power of plus close square brackets space equals space straight K subscript straight w over straight c square root of fraction numerator straight K subscript straight a straight c over denominator straight K subscript straight w end fraction end root
space space space space space space space space space space space space space space space space space space space space space equals space square root of fraction numerator straight K subscript straight w. space straight K subscript straight a over denominator straight c end fraction end root
therefore space space space space space pH space equals space minus log space open square brackets straight H to the power of plus close square brackets
space space space space space space space space space space space space space equals negative log space square root of fraction numerator straight K subscript straight w. space straight K subscript straight a over denominator straight c end fraction end root
space space space space space space space space space space space space equals negative log space open parentheses fraction numerator straight K subscript straight w. space straight K subscript straight c over denominator straight c end fraction close parentheses to the power of 1 divided by 2 end exponent
pH space equals space minus 1 half open square brackets log space straight K subscript straight W space plus space log space straight K subscript straight a space minus space log space straight c close square brackets space space space space space space space space space space space space
    Question 282
    CBSEENCH11006581

    Derive space straight K subscript straight h space equals space fraction numerator straight K subscript straight w over denominator straight K subscript straight a space straight K subscript straight b end fraction
for space straight a space solution space of space salt space of space weak space acid space and space weak space base.

    Solution
    Suppose the salt of weak acid and weak base is BA and its hydrolysis is represented as:
         BA with salt below space plus space straight H subscript 2 straight O space space space leftwards harpoon over rightwards harpoon space space space space BOH with weak below space plus space HA with weak below
    or space space straight B to the power of plus space space plus straight A to the power of minus space plus space straight H subscript 2 straight O space space space rightwards harpoon over leftwards harpoon space space space space BOH space plus space HA
    It involves both cationic as well as ionic hydrolysis.
    Now space space space space space space space space straight K subscript straight h space equals space fraction numerator open square brackets BOH close square brackets space open square brackets HA close square brackets over denominator open square brackets straight B to the power of plus close square brackets space open square brackets straight A to the power of minus close square brackets end fraction space space space space space space space space space... left parenthesis 1 right parenthesis
    Also for weak acid, 
                        space space space HA space rightwards harpoon over leftwards harpoon space space space straight H to the power of plus space plus space straight A to the power of minus
space space space straight K subscript straight a space equals space fraction numerator open square brackets straight H to the power of plus close square brackets space open square brackets straight A to the power of minus close square brackets over denominator open square brackets HA close square brackets end fraction space space space space space... left parenthesis 2 right parenthesis
    For weak base, 
            BOH space space rightwards harpoon over leftwards harpoon space space space space straight B to the power of plus space plus space OH to the power of minus
straight K subscript straight b space equals space fraction numerator open square brackets straight B to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets over denominator open square brackets BOH close square brackets end fraction space space space space space space space space space space space space space space space space... left parenthesis 3 right parenthesis

    Also space space straight K subscript straight W space equals space open square brackets straight H close square brackets to the power of plus space open square brackets OH to the power of minus close square brackets space space space space space... left parenthesis 4 right parenthesis
Multiplying space equations space left parenthesis 1 right parenthesis comma space left parenthesis 2 right parenthesis space and space left parenthesis 3 right parenthesis comma
straight K subscript straight h space. space straight K subscript straight a space. space straight K subscript straight b space equals space open square brackets straight H to the power of plus close square brackets space open square brackets OH to the power of plus close square brackets
space space space space space space space space space space space space space space space space space space equals space straight K subscript straight w space space space space space space space space space space space space space left square bracket From space eq. space left parenthesis 4 right parenthesis right square bracket
space space therefore space space space space space space space straight K subscript straight h space equals space fraction numerator straight K subscript straight w over denominator straight K subscript straight a space straight K subscript straight b end fraction space space space space space space space space space space space space space space space space space space space space

    Question 283
    CBSEENCH11006582

    Derive space straight K subscript straight h space equals space fraction numerator straight K subscript straight w over denominator straight K subscript straight a space straight K subscript straight b end fraction
for space straight a space solution space of space salt space of space weak space acid space and space weak space base.

    Solution
    Suppose the salt of weak acid and weak base is BA and its hydrolysis is represented as:
             BA with salt below space plus space straight H subscript 2 straight O space space leftwards harpoon over rightwards harpoon space space space BOH with weak below space plus space HA with weak below
    or space space straight B to the power of plus space plus space straight A to the power of minus space space plus space straight H subscript 2 straight O space space rightwards harpoon over leftwards harpoon space space space space BOH space plus space HA
    It involves both cationic as well as ionic hydrolysis.
    Now comma space space space straight K subscript straight h space equals space fraction numerator open square brackets BOH close square brackets open square brackets HA close square brackets over denominator open square brackets straight B to the power of plus close square brackets open square brackets straight A to the power of minus close square brackets end fraction space space space space space space space space... left parenthesis 1 right parenthesis
Also space for space weak space acid comma space
space space space space space space HA space rightwards harpoon over leftwards harpoon space space straight H to the power of plus space plus space straight A to the power of minus
space space space space space space straight K subscript straight a space equals space fraction numerator open square brackets straight H to the power of plus close square brackets open square brackets straight A to the power of minus close square brackets over denominator open square brackets HA close square brackets end fraction space space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis
For space weak space base comma
space space space space space space BOH space leftwards harpoon over rightwards harpoon space space straight B to the power of plus space plus space OH to the power of minus
space space space space space straight K subscript straight b space space equals space fraction numerator open square brackets straight B to the power of plus close square brackets open square brackets OH to the power of minus close square brackets over denominator open square brackets BOH close square brackets end fraction space space space space space space space space space space space space space space... left parenthesis 3 right parenthesis

    Also comma space space space space straight K subscript straight w space equals space open square brackets straight H to the power of plus close square brackets space open square brackets OH to the power of minus close square brackets space space space space space space space space space... left parenthesis 4 right parenthesis
    Multiplying equations (1), (2) and (3),
    straight K subscript straight h. space straight K subscript straight a space. space straight K subscript straight b space equals space open square brackets straight H to the power of plus close square brackets space open square brackets OH to the power of plus close square brackets space equals space straight K subscript straight w space space space space left square bracket From space eq. space left parenthesis 4 right parenthesis right square bracket
space space therefore space space space space space space straight K subscript straight h space equals space fraction numerator straight K subscript straight w over denominator straight K subscript straight a space straight K subscript straight b end fraction
    Question 284
    CBSEENCH11006583

    Show that degree of hydrolysis of a salt of weak acid and weak base is independent of concentration of the solution.
    Or
    Derive the relation,  straight alpha space equals square root of fraction numerator straight K subscript straight w over denominator straight K subscript straight a. space straight K subscript straight b space end fraction end root in case of hydrolysis of a salt of weak acid and weak base.

    Solution
    Let us consider the example of ammonium acetate.
    Let c be the initial concentration of ammonium acetate in moles per litres and a be the degree of hydrolysis. The equilibrium concentration of various species are:
                             CH subscript 3 COO to the power of minus space plus space NH subscript 4 superscript plus space plus space straight H subscript 2 straight O space space space rightwards harpoon over leftwards harpoon space space space space space CH subscript 3 COOH space plus space space NH subscript 4 OH
    Initial conc.               c             c                                  0                    0
    Equilibriumstraight c left parenthesis 1 minus straight alpha right parenthesis space straight c left parenthesis 1 minus straight alpha right parenthesis                                         cα                  cα
    conc. 
                         straight K subscript straight h space equals space fraction numerator cα space cross times space cα over denominator straight c left parenthesis 1 minus straight alpha right parenthesis space cross times space straight c left parenthesis 1 minus straight alpha right parenthesis end fraction space equals space fraction numerator straight alpha squared over denominator left parenthesis 1 minus straight alpha squared right parenthesis end fraction
    Since straight alpha is very small as compared to unity,
    therefore space space space 1 minus space straight alpha space equals space 1
therefore space space space space space straight K subscript straight h space equals space straight alpha squared
or space space space space space straight alpha space equals space square root of straight K subscript straight h end root
AS space space straight K subscript straight h space equals space fraction numerator straight K subscript straight w over denominator straight K subscript straight a space cross times space straight K subscript straight b end fraction
therefore space space space space straight alpha space equals space space square root of fraction numerator straight K subscript straight w over denominator straight K subscript straight a space cross times space straight K subscript straight b end fraction end root
    Hence degree of hydrolysis (R) is independent of the concentration of the solution.
    Question 285
    CBSEENCH11006584

    A 0·02M solution of pyridinium hydrochloride has pH = 3·44. Calculate the ionisation constant of pyridine.

    Solution
    Pyridine hydrochloride is a salt of a weak base and strong acid. Hence
       space space space space space space pH space equals space minus 1 half open square brackets log space straight K subscript straight w space minus space log space straight K subscript straight b space plus space log space straight C close square brackets
           
    or space space 3.44 space equals space minus 1 half open square brackets negative 14 minus log space straight K subscript straight b space plus space log space left parenthesis 2 space cross times space 10 to the power of negative 2 end exponent right parenthesis close square brackets
or space space space 6.88 space equals space 14 space plus space log space straight K subscript straight b space plus space 1.70
or space space log space straight K subscript straight b space equals space minus 8.82 space equals space minus 8 minus 1 plus 1 space minus space 0.82 space equals space 9 with bar on top.18
space space space space space space straight K subscript straight b space equals space antilog space left parenthesis 9 with bar on top space.18 right parenthesis space equals space 1.5 space cross times space 10 to the power of negative 9 end exponent
    Question 286
    CBSEENCH11006585

    The ionisation constant of nitrous acid is 4·5 × 10–4. Calculate the pH of 0·04M sodium nitrite solution and also its degree of hydrolysis.

    Solution
    Sodium nitrite is a salt of a strong base and a weak acid. Its degree of hydrolysis, h is given by the relation:
    straight h space equals space square root of fraction numerator straight K subscript straight w over denominator straight K subscript straight a space cross times space straight C end fraction end root space equals space square root of fraction numerator 1 space cross times space 10 to the power of negative 14 end exponent over denominator 4.5 space cross times space 10 to the power of negative 4 end exponent space cross times space 0.04 end fraction end root
space space space equals space space square root of 5.56 space cross times space 10 to the power of negative 10 end exponent end root
space space space equals space 2.36 space cross times space 10 to the power of negative 5 end exponent
space space We space know comma space
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#11 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(80): com_wiris_plugin_impl_HttpImpl->request(true)
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#13 {main}</pre>
    Question 289
    CBSEENCH11006588

    Calculate the pH of 0.1M solution of sodium acetate (pKa = 4·74).

    Solution
    Since sodium acetate is a salt of weak acid and strong base,
    therefore space space space pH space equals space minus 1 half open square brackets log space straight K subscript straight w space plus space log space straight K subscript straight a space minus space log space straight c close square brackets
space space space space space space space space space space equals space 1 half open square brackets negative log space straight K subscript straight w space minus space log space straight K subscript straight a space plus space log space straight c close square brackets
space space space space space space space space space space equals space 1 half left square bracket pK subscript straight w space plus space pK subscript straight a space plus space log space straight c right square bracket
space space space space space space space space space space space equals 1 half open square brackets negative log space left parenthesis 10 to the power of negative 14 end exponent right parenthesis space plus space 4.74 space plus space log space 0.01 close square brackets
space space space space space space space space space space space equals 1 half left square bracket 14 plus 4.74 plus log space 10 to the power of negative 2 end exponent right square bracket
space space space space space space space space space space space space equals space 0.5 open square brackets 14 space plus space 4.74 space minus space 2 close square brackets
space space space space space space space space space space space space equals space 0.5 space cross times 16.74 space equals space 8.37 space space space space space space space space space space space space space space space space space space
space space space space space space space
    Question 290
    CBSEENCH11006589

    The ionisation constant of chloroacetic acid is 1·35 × 10–3. What will be the pH of 0·1M acid and its 0·1M sodium salt solution?

    Solution
    Chloroacetic acid ionises as,
    ClCH subscript 2 COOH space space rightwards harpoon over leftwards harpoon space space ClCH subscript 2 COO to the power of minus space plus space straight H to the power of plus
therefore space space space space space straight K subscript straight a space equals space fraction numerator open square brackets ClCH subscript 2 COO to the power of minus close square brackets space open square brackets straight H to the power of plus close square brackets over denominator open square brackets ClCH subscript 2 COOH close square brackets end fraction
In space this space case comma space open square brackets ClCH subscript 2 COO to the power of minus close square brackets space equals space open square brackets straight H to the power of plus close square brackets
therefore space space space straight K subscript straight a space equals space open square brackets straight H to the power of plus close square brackets squared over straight C
space therefore space space space space open square brackets straight H to the power of plus close square brackets space equals space square root of straight K subscript straight a space cross times space straight C end root
                 equals space square root of 1.35 space cross times space 10 to the power of negative 3 end exponent space cross times space 0.1 end root
equals space 1.16 space cross times space 10 to the power of negative 2 end exponent
    But space space space pH space equals space minus log space open square brackets straight H to the power of plus close square brackets space equals space minus log space left parenthesis 1.16 space cross times space 10 to the power of negative 2 end exponent right parenthesis
space space space space space space space space space space space space space equals space 2 minus log space 1.16 space equals space 2 minus 0.06 space equals space 1.94 space space space space space space space space space space space space space
    Since sodium salt of chloroacetic acid is a salt of strong base and weak acid, therefore,
                           pH space equals space minus 1 half open square brackets log space straight K subscript straight w space plus space log space straight K subscript straight a space minus space log space straight C close square brackets
space space space space equals negative 1 half open square brackets log space 10 to the power of negative 14 end exponent space plus space log space 1.35 space cross times space 10 to the power of negative 3 end exponent space minus space log space 0.1 close square brackets
space space space space space equals negative 1 half open square brackets negative 14 plus left parenthesis negative 3 plus 0.1303 close square brackets space minus left parenthesis negative 1 right parenthesis right square bracket
space space space space space equals space 7 plus 1.44 minus 0.5
space space space space space space equals space 7.94
    Question 291
    CBSEENCH11006590
    Question 292
    CBSEENCH11006591

    Explain the terms: buffer solution and buffer capacity.

    Solution

    Buffer solution: A buffer solution may be defined as a solution which resists change in its pH on the addition of water or small amount of acid or base. The ability of the buffer solution to resist change in its pH on the addition of acid or base is called buffer action.

    Types of buffer solutions : Buffer solutions are of two types:
    (i) Acidic buffer. An acidic buffer is a mixture (equimolar) of a weak acid and its salt with strong base. For example CH3COOH and CH3COONa ; H2CO3 ; H3PO4 and K3PO4.
    (ii) Basic buffer. A basic buffer is a mixture (equimolar) of a weak base and its salt with strong acid. For example NH4OH and NH4Cl ; Ca(OH)and CaSO4.
    Buffer capacity or Buffer index: The buffer capacity is defined as the amount (number of moles) of the acid or base which when added to 1 litre of the given buffer solution change its pH by unity i.e. 
               Buffer space capacity space left parenthesis straight beta right parenthesis
space space space space space space space space equals space fraction numerator No. space of space moles space of space acid space or space alkali space added divided by litre over denominator Change space in space pH end fraction
Mathematically comma space space straight beta space equals space fraction numerator straight d open square brackets straight B close square brackets over denominator dpH end fraction space space space or space space space fraction numerator straight d open square brackets straight A close square brackets over denominator dpH end fraction
    where d[B] = change in the concentration of base
              d[A] = change in the concentration of acid
      or     dpH = change in pH of the buffer solution
         Buffer capacity is always positive, because
      (i) On adding acid to buffer, its pH is decreased i.e. d[A] is positive but dpH is negative so that negative fraction numerator straight d open square brackets straight A close square brackets over denominator dpH end fraction space space or space space space straight beta space is space positive.
    (ii) On adding base to a buffer solution, its pH increases, i.e. d[B] and dpH are both positive and hence fraction numerator straight d open square brackets straight B close square brackets over denominator dp left square bracket straight H right square bracket end fraction space or space space straight beta space is space positive.
     

    Question 293
    CBSEENCH11006592

    Show with an example how buffer solution resists the action of acid or base towards change in pH.
    Or
    Discuss the buffer action of:
    (i) acidic buffer
    (ii) basic buffer.

    Solution
    The action of acidic buffer: Consider an equimolar mixture of CH3COONa (strong electrolyte) and CH3COOH (weak electrolyte).
    CH subscript 3 COOH space space rightwards harpoon over leftwards harpoon space space space space CH subscript 3 COO to the power of minus left parenthesis aq right parenthesis space plus space straight H to the power of plus left parenthesis aq right parenthesis
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space left square bracket weakly space ionised right square bracket
CH subscript 3 COONa space space rightwards arrow space space space stack CH subscript 3 COO to the power of minus left parenthesis aq right parenthesis with common space ion below space plus space stack Na to the power of plus left parenthesis aq right parenthesis space with left square bracket fully space ionised right square bracket below space space space space
    Ionisation of acetic acid is suppressed by acetate ion[common ion effect].
    There will be a large concentration of Na+ ions. CH3COO ions and undissociated CH3COOH molecules.
    (i) When a few drops of acid (say HCl) are added to it, the H+ ion from the added acid combines with an excess of CH3COO ion to form feebly ionised CH3COO ion to form feebly ionised CH3COOH.
    stack CH subscript 3 COO to the power of minus with left parenthesis In space buffer right parenthesis below space plus space stack straight H to the power of plus with left parenthesis From space acid right parenthesis below space space space leftwards harpoon over rightwards harpoon space space space space CH subscript 3 COOH
    Thus there is no increase in the concentration of H+ ions, pH remains constant.
    (ii) When a few drops of a base (say NaOH) are added, OH ions of the added base are neutralised by the H+ ions (of buffer) to form feebly ionised water molecules.
    stack straight H to the power of plus with left parenthesis From space buffer space CH subscript 3 COOH right parenthesis below space space plus space space space space stack OH to the power of minus with left parenthesis From space base right parenthesis below space space space rightwards arrow space space space straight H subscript 2 straight O
    Thus there is no increase in the concentration of OH ions and hence pH remains constant.
    The reverse acidity is due to CH3COOH and reserves basicity to due to CH3COO ions.
    The action of basic buffer: A basic buffer is a mixture (equimolar) of a weak base and its salt with a strong acid. Consider an equimolar mixture of NH4OH (weak electrolyte) and NH4Cl (strong electrolyte).

    Ionisation of NH4OH is suppressed by NH+ ions [common ion effect].
    There will be a large concentration of NH4+ ions, Cl ions and NH4OH molecules.
    (i) When a few drops of acid (say HCl) are added, the H+ ions of the added acid combine with OH- ions of-NH4OH (of buffer) to form feebly ionised water. Thus no change in pH occurs.
    stack straight H to the power of plus with left parenthesis from space acid right parenthesis below space space plus space stack OH to the power of minus with left parenthesis from space buffer right parenthesis below space space rightwards arrow space space space space straight H subscript 2 straight O
    According to Le Chatelier’s principle, the above reaction results in the greater dissociation of NH4OH to restore the original concentration of OH ions.
    NH subscript 4 OH space rightwards harpoon over leftwards harpoon space space space NH subscript 4 superscript plus space space plus space OH to the power of minus
    (ii) When a few drops of a base (say NaOH) are added to the buffer, the OH ions of added base combine with NH4+ ions to form unionised NH4OH.
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#13 {main}</pre>

    As the concentration of OH ions does not increase, the pH value remains unchanged.
    In this buffer, reserve acidity is due to NH4+ ions and reserve alkalinity is due to NH4OH molecules.

     

    Question 294
    CBSEENCH11006593

    How will you explain buffer action of aqueous solution of ammonium acetate?

    Solution
    Ammonium acetate on dissolution dissociates completely as ions.
    CH subscript 3 COONH subscript 4 left parenthesis aq right parenthesis space space rightwards arrow space space space CH subscript 3 COO to the power of minus left parenthesis aq right parenthesis space plus space NH subscript 4 superscript plus space left parenthesis aq right parenthesis
    (i) If an acid (say HCl) is added to this solution, H3O+ ions generated by the acid combine with CH3COO ion to form weakly ionised acetic acid molecules
    stack CH subscript 3 COO with left parenthesis Buffer right parenthesis below left parenthesis aq right parenthesis space plus space straight H subscript 3 straight O to the power of plus space space space space rightwards arrow space space space space space stack CH subscript 3 COOH with left parenthesis weakly space ionised right parenthesis below space plus space straight H subscript 2 straight O
    Since most of H3O+ ions are consumed by CH3COO ions to form slightly dissociated acetic acid, hence the pH value of the solution does not undergo any change.
    Now suppose a base (say NaOH) is added to ammonium acetate solution. The OH ions liberated by the base will be consumed by NH subscript 4 superscript plusions to form very slightly dissociated NH4OH. 

    stack NH subscript 4 superscript plus left parenthesis aq right parenthesis with From space buffer below space plus space OH to the power of minus space left parenthesis aq right parenthesis space space rightwards arrow space space NH subscript 4 OH
    Since most of the OH ions are consumed by the NH subscript 4 superscript plus ions, hence there is very little or no change in the pH value of ammonium acetate.
    Thus, CH3COONH4 has reserve acidity due to NH subscript 4 superscript plus ions and reserve alkalinity due to CH3COO ions.
    Question 295
    CBSEENCH11006594

    Calculate the pH of:
    (i) an acidic buffer mixture 
    (ii) a basic buffer mixture.
    Or
    Derive Henderson’s equation for an acidic and basic buffer mixture.
    Or
    Derive the following equation for the pH of an acidic buffer:
    pH space equals space pK subscript straight a space plus space log space fraction numerator open vertical bar Salt close vertical bar over denominator open vertical bar Acid close vertical bar end fraction

    Solution
    For acidic buffer mixture: Consider an acid buffer. Let it be a mixture of HA (weak acid) and its salt with a strong base, BA. A weak acid is only ionised to a small extent.
    HA space rightwards harpoon over leftwards harpoon space space space straight H to the power of plus space plus space space straight A to the power of minus
    Applying the law of chemical equilibrium, we get,
                         straight K subscript straight a space equals space fraction numerator open square brackets straight H to the power of plus close square brackets space open square brackets straight A to the power of minus close square brackets over denominator open square brackets HA close square brackets end fraction
where space straight K subscript straight a space is space the space dissociation space constant space of space the space acid. space
therefore space space space space space space space space open square brackets straight H to the power of plus close square brackets space equals space straight K subscript straight a space fraction numerator open square brackets HA close square brackets over denominator open square brackets straight A to the power of minus close square brackets end fraction space space space space space space space space space space... left parenthesis 1 right parenthesis
The space salt space BA space being space strong space electrolyte space dissociates space
almost space completely space in space the space solution.
space space space space BA space space rightwards arrow space space space straight B to the power of plus space plus space straight A to the power of minus
    Due to the increase in the concentration of A ions the dissociation of the weak acid is further suppressed due to common ion effect. The concentration of weak acid molecules is taken as the concentration of HA and the concentration of the salt is the concentration of A ions. Thus,
    [HA] = [Acid]
    [BA] = [A-] = [Salt]
    Substituting the values of [HA] and [A] in expression (1), we have.
    open square brackets straight H to the power of plus close square brackets space equals space straight K subscript straight a space fraction numerator open square brackets Acid close square brackets over denominator open square brackets Salt close square brackets end fraction
    Taking logarithm of both the sides, we get,
    log space open square brackets straight H to the power of plus close square brackets space equals space log space straight K subscript straight a space plus space log space fraction numerator open square brackets Acid close square brackets over denominator open square brackets Salt close square brackets end fraction
or space space space minus log space open square brackets straight H to the power of plus close square brackets space equals space minus log space straight K subscript straight a space minus space log space fraction numerator open square brackets Acid close square brackets over denominator open square brackets Salt close square brackets end fraction
or space space space space space pH space equals space pK subscript straight a space plus space log space fraction numerator open square brackets Salt close square brackets over denominator open square brackets Acid close square brackets end fraction
    This equation is known as Henderson equation. It helps in calculating the pH value of the buffer solution if the concentration of acid, as well as the salt, is known.
    For basic buffer mixture: Proceeding exactly in a similar way as above, the expression for the pH of a basic buffer mixture (BOH + BA) can be obtained. BOH being a weak base dissociates to a small extent.
    space space space space space space space space space space space BOH space space space rightwards harpoon over leftwards harpoon space space space straight B to the power of plus space plus space OH to the power of minus
or space space space space space space space space space space straight K subscript straight b space equals space fraction numerator open square brackets straight B to the power of plus close square brackets open square brackets OH to the power of minus close square brackets over denominator open square brackets BOH close square brackets end fraction
where space straight K subscript straight b space is space the space dissociation space constant space of space the space base comma space
or space space space space space open square brackets OH to the power of minus close square brackets space equals space straight K subscript straight b space cross times space fraction numerator open square brackets BOH close square brackets over denominator open square brackets straight B to the power of plus close square brackets end fraction space space space space space space space... left parenthesis 1 right parenthesis
    The salt BA being strong electrolyte dissociates almost completely. 
                                 space space space space space space BA space space rightwards arrow space space space straight B to the power of plus space plus space straight A to the power of minus
Now space space space space space open square brackets BOH close square brackets space equals space open square brackets Base close square brackets
space space space open square brackets BA close square brackets space equals open square brackets straight B to the power of plus close square brackets space equals space open square brackets Salt close square brackets
Substituting space the space values space of space open square brackets BOH close square brackets space and space open square brackets straight B to the power of plus close square brackets space
in space expression space left parenthesis 1 right parenthesis comma space we space have comma space
space space space open square brackets OH to the power of minus close square brackets space equals space straight K subscript straight b space cross times space fraction numerator open square brackets Base close square brackets over denominator open square brackets Salt close square brackets end fraction
    Taking logarithm of both the sides we get,
         log space open square brackets OH to the power of minus close square brackets space equals space log space straight K subscript straight b space plus space log space fraction numerator open square brackets Base close square brackets over denominator open square brackets Salt close square brackets end fraction
minus log space open square brackets OH to the power of minus close square brackets space equals space minus log space straight K subscript straight b space minus space log space fraction numerator open square brackets Base close square brackets over denominator open square brackets Salt close square brackets end fraction
pOH space equals space pK subscript straight b space plus space log space fraction numerator open square brackets Salt close square brackets over denominator open square brackets Base close square brackets end fraction space space space space space space space space... left parenthesis 2 right parenthesis
    This is also called Henderson equation. The pH of the basic buffer solution can be obtained by the following expression:
            pH space plus space pOH space equals space 14
or space space space space space space space space space space pH space space equals space 14 space minus space pOH
Substituting space the space values space of space pOH comma
space space pH space equals space 14 minus space pK subscript straight b space minus space log space fraction numerator open square brackets Salt close square brackets over denominator open square brackets Base close square brackets end fraction
    Question 296
    CBSEENCH11006595

    Calculate the pH value of a solution obtained by mixing 0·083 moles of acetic acid and 0·091 moles of sodium acetate and making the volume 500 ml. Ka for acetic acid is 1·75 × 10–5.

    Solution
    For acidic buffer, Henderson equation is
    pH space equals space pK subscript straight a space plus space log space fraction numerator open square brackets Salt close square brackets over denominator open square brackets Acid close square brackets end fraction space space... left parenthesis 1 right parenthesis
Here space open square brackets Acid close square brackets space equals space open square brackets CH subscript 3 COOH close square brackets
space space space space space space space space space space space space space space space equals space fraction numerator 0.083 over denominator 500 end fraction space cross times space 1000 space equals space 0.166 space mol space straight L to the power of negative 1 end exponent
space space space space space space space space space space space open square brackets Salt close square brackets space equals space open square brackets CH subscript 3 COONa close square brackets
space space space space space space space space space space space space space space space space space space space space equals fraction numerator 0.091 over denominator 500 end fraction cross times 1000 space equals space 0.182 space mol space straight L to the power of negative 1 end exponent
space space space space space space space space space pK subscript straight a space equals space minus log space straight K subscript straight a
space space space space space space space space space space space space space space space space equals negative log space open square brackets 1.75 space space cross times 10 to the power of negative 5 end exponent close square brackets space equals space 4.757 space space space space space space space space space space space space space space space space space space space space space
    Substituting the values in equation (1), we get, 
    pH space equals space 4.757 space plus space log space fraction numerator 0.182 over denominator 0.166 end fraction
space space space space space equals space 4.757 space plus space 0.040 space equals space 4.797
                    
    Question 297
    CBSEENCH11006596

    Calculate the pH of a solution obtained by mixing 6·0g of acetic acid and 12·30g of sodium acetate and making the volume of solution to 500 ml. Ka for acetic acid is 1·8 × 10–5

    Solution
    Molecular space mass space of space acetic space acid comma space space left parenthesis CH subscript 3 COOH right parenthesis space equals 60
Molecular space mass space of space sodium space acetate comma space left parenthesis CH subscript 3 COONa right parenthesis space equals space 82
open square brackets CH subscript 3 COOH close square brackets space equals fraction numerator 6.0 over denominator 60 end fraction cross times 1000 over 50 space equals 0.2 space straight M
open square brackets CH subscript 3 COONa close square brackets space equals space fraction numerator 12.30 over denominator 82 end fraction cross times 1000 over 500 space equals 0.3 space straight M
    For acidic buffer, Henderson equation is
         pH space equals space pK subscript straight a space plus space log space fraction numerator open square brackets Salt close square brackets over denominator open square brackets Acid close square brackets end fraction space space space... left parenthesis 1 right parenthesis
Now space space pK subscript straight a space equals space minus log space straight K subscript straight a
space space space space space space space space space space space space space space equals negative log space left parenthesis 1.8 space cross times space 10 to the power of negative 5 end exponent right parenthesis
space space space space space space space space space space space space space space equals negative left square bracket log space 1.8 space plus space log space 10 to the power of negative 5 end exponent right square bracket
space space space space space space space space space space space space space space equals negative open square brackets log space 1.8 space minus 5 close square brackets
space space space space space space space space space space space space space space equals plus 5 space minus space log space 1.8
therefore space space space space pK subscript straight a space space equals space 4.7417 space space space space space space space space space

    Substituting the values in equation (1), we get,
         pH space equals space 4.7447 space plus space log space fraction numerator open square brackets 0.3 close square brackets over denominator open square brackets 0.2 close square brackets end fraction space equals space 4.9248

    Question 298
    CBSEENCH11006597

    Determine the pH of a solution obtained by mixing equal volumes of 0·015N NH4OH and 0·15N NH4NO3 solutions. (Kb for NH4OH is 1·8 × 10–5).

    Solution
    For a basic buffer, Henderson equation is
    pOH space equals space pK subscript straight b space plus space log space fraction numerator open square brackets Salt close square brackets over denominator open square brackets Base close square brackets end fraction space space space space... left parenthesis 1 right parenthesis
    Here,  on mixing equal volumes of two solutions,
         open square brackets NH subscript 4 OH close square brackets space equals space space fraction numerator 0.015 over denominator 2 end fraction space equals 0.0075 space straight N
open square brackets NH subscript 4 NO subscript 3 close square brackets space equals space fraction numerator 0.015 over denominator 2 end fraction equals space 0.075 space straight N
space space space space space space pK subscript straight b space equals space log space straight K subscript straight b
space space space space space space space space space space space space space equals log space left parenthesis 1.8 space cross times space 10 to the power of negative 5 end exponent right parenthesis
space space space space space space space space space space space
    Substituting the values in equation (1), we get,
     
        pOH space equals space 4.7447 space plus space log space fraction numerator 0.075 over denominator 0.0075 end fraction
space space space space space space space equals 4.7447 space plus space log space 10
space space space space space space space equals 4.7447 space plus 1 space equals space 5.7447
But space pH space plus space pOH space equals space 14
therefore space space space space pH space equals space 14 space minus space pOH
space space space space space space space space space space space space equals space 14 minus 5.7447 space equals space 8.2553
    Question 299
    CBSEENCH11006598

    Describe Ostwald’s theory of acid-base indicators.
    Or
    How does Ostwald’s theory explain the colour change of:
    (i) Phenolphthalein
    (ii) Methyl orange in acid-base titrations?

    Solution

    (i) Ostwald’s theory: According to this theory, an acid-base indicator is either a weak organic acid or a weak organic base whose undissociated molecule has a. colour different from the ions furnished by it. These different coloured ions are produced in the solution under the influence of a strong acid or a strong base.
    To understand this theory, consider the case of phenolphthalein which is written as HPh. It is a weak acid. Its undissociated molecules are colourless. When its molecules are dissociated, they give colourless H+ ions and deep pink coloured Ph+ ions.
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#13 {main}</pre>
    When phenolphthalein is added to the acidic solution, the dissociation of phenolphthalein is practically nil due to increasing the concentration of hydrogen ions. It means that the solution remains colourless.
    When strong alkali is added to the phenolphthalein, OH ions furnished by alkali combine with H+ ions furnished by phenolphthalein to form feebly ionised water and sodium salt NaPh. The NaPh remains in ionic state and imparts a pink colour to it. This is explained as follows:

    Similarly, this theory also explains the action of methyl orange. It is a weak base and may be, represented as MeOH. Its undissociated molecules are yellow while its ions (Me+) are red. thus,
    MeOH with Yellow below space space leftwards harpoon over rightwards harpoon space space space stack Me to the power of plus with Red below space space space plus space stack OH to the power of minus with Colourless below
    When a base is added to MeOH. the OH ions of alkali suppress the ionisation of MeOH so that the solution of MeOH is yellow in colour. When an acid is added to MeOH. the H+ ions furnished by acid combine with MeOH to form feebly ionised water along with the formation of MeCl. The McCl. is strongly ionised to give a large concentration of Meions, thereby producing a pink-red colour. Thus, in the acid solution, methyl orange gives a pink-red colour.

    Ostwald’s theory does not explain the cause of colour changes in the indicator.

    Question 300
    CBSEENCH11006599

    How does the concept of solubility product help in finding out the solubility of sparingly soluble salts?

    Solution
    The concept of solubility product is helpful in finding out the solubility of the sparingly soluble salts in water if their Ksp values are known. For example, let AB be a sparingly soluble salt and suppose S mol L–1 be the solubility of AB.
    stack AB left parenthesis straight s right parenthesis with straight S space mol space straight L to the power of minus below space space space rightwards harpoon over leftwards harpoon with Water on top space space stack straight A to the power of plus left parenthesis aq right parenthesis with straight S space mol space straight L to the power of negative 1 end exponent below space plus space stack straight B to the power of minus left parenthesis aq right parenthesis with straight S space mol space straight L to the power of negative 1 end exponent below
    Applying the law of solubility equilibrium,
       straight K subscript sp space equals space open square brackets straight A to the power of plus close square brackets space open square brackets straight B to the power of minus close square brackets
space space straight K subscript sp space equals space straight S space cross times space straight S
      or space space space straight S squared space space equals space straight K subscript sp
therefore space space straight S space equals space square root of straight K subscript sp end root
    Knowing the solubility product Ksp (from tables), solubility can be calculated.
    Question 301
    CBSEENCH11006600

    How does the concept of solubility product help in predicting the ionising and precipitating nature of a salt?

    Solution

    Knowing the solubility product of a salt, it is possible to predict that on mixing the solutions of its ions, a precipitate will be formed or not. For the precipitation to occur, its ionic product should exceed its solubility product. Therefore, to predict the precipitation reaction, we just calculate the ionic product of the ions and find out whether it is greater than Ksp or not. If
    Ionic product > Ksp, precipitation occurs;
    Ionic product < Ksp, no precipitation occurs.
    Ionic product = Ksp, the solution is just saturated and no precipitation occurs.

    Question 302
    CBSEENCH11006601

    Give the main points of difference between solubility product and ionic product.

    Solution

    Solubility product

    Ionic product

    1. It is applicable to saturated solution.

    1. It is applicable to any kind of solution.

    2. It is the product of the concentrations of the ions of the electrolyte each concentration raised to the power equal to the number of times each ion occurs in the equation in a saturated solution.

    2. It is the product of the concentrations of the ions of the electrolyte. Each concentration raised to the power equal to the number of times each ion occurs in the equation in solution at any concentration.

    3. It is constant for a given electrolyte at a given temperature.

    3. Its value is not constant and varies with change in concentration of the ions.

    Question 303
    CBSEENCH11006602

    Give the points of difference betw een solubility and solubility product.

    Solution

    Solubility

    Solubility product

    1. It is applicable to electrolytes such as NaCl as well as non-electrolytes such as urea.

    1. It can be increased or decreased in case of electrolytes by common ions even at constant temperature.

    2. It is applicable only to electrolytes like urea.

    2. Ksp remains constant at a particular temperature.

    Question 304
    CBSEENCH11006603

    The solubility of silver chloride is 1·06×10–5 mole per litre at 298K. Find its solubility product.

    Solution
    We know,
    AgCl left parenthesis straight s right parenthesis space space space space space space space rightwards harpoon over leftwards harpoon space space space space space space space space Ag to the power of plus space left parenthesis aq right parenthesis space space space space space space space space space space plus space space space Cl to the power of minus left parenthesis aq right parenthesis straight s
1.06 space cross times 10 to the power of negative 5 end exponent space mol space space space space space space space space 1.06 space cross times 10 to the power of negative 5 end exponent mol space space space space space 1.06 cross times 10 to the power of negative 5 end exponent space mol space space
    Applying the law of solubility product
                straight K subscript sp space equals space open square brackets Ag to the power of plus close square brackets space space open square brackets Cl to the power of minus close square brackets
space space space space space space equals space left parenthesis 1.06 space cross times 10 to the power of negative 5 end exponent right parenthesis thin space left parenthesis 1.06 space cross times space 10 to the power of negative 5 end exponent right parenthesis
space space space space space space equals space 1.12 space cross times space 10 to the power of negative 10 end exponent
    Hence the solubility product of silver chloride
                            equals space 1.12 space cross times space 10 to the power of negative 10 end exponent.
    Question 305
    CBSEENCH11006604

    The solubility of Ag2CrO4 at 298K is 6·6 × 10–5 moles/litre. Find its solubility product.

    Solution
    We know,
    Ag subscript 2 CrO subscript 4 space space space rightwards harpoon over leftwards harpoon space space space space 2 Ag to the power of plus space plus space CrO subscript 4 superscript 2 minus end superscript
    Now 1 mole of  on dissociation gives 2 moles of Ag+ ions and 1 mole of CrO subscript 4 superscript 2 minus end superscript ions. 
    2 space moles space of space Ag to the power of plus space ions space and space 1 space mole space of space CrO subscript 4 superscript 2 minus end superscript space ions.
Hence comma space
open square brackets Ag to the power of plus close square brackets space equals space 2 space cross times space 6.6 space cross times space 10 to the power of negative 5 end exponent mol space straight L to the power of negative 1 end exponent
open square brackets CrO subscript 4 superscript 2 minus end superscript close square brackets space equals space 6.6 space cross times 10 to the power of negative 5 end exponent space mol space straight L to the power of negative 1 end exponent
Applying space the space law space of space solubility space product comma space
straight K subscript sp space equals space open square brackets Ag to the power of plus close square brackets squared space open square brackets CrO subscript 4 superscript 2 minus end superscript close square brackets
space space space space space space equals space left parenthesis 2 space cross times space 6.6 space cross times space 10 to the power of negative 5 end exponent right parenthesis squared space left parenthesis 6.6 space cross times space 10 to the power of negative 5 end exponent right parenthesis
space space space space space space equals 1.149 space cross times space 10 to the power of negative 12 end exponent
space space
    Question 306
    CBSEENCH11006605

    At 298K, the, solubility of silver chloride in water is 0·00188 gL. What is its Ksp?

    Solution
    Molecular mass of AgCl
                                 =  108  + 35.5  = 143.5 
    Solubility of AgCl in water = 0.00188 gL-1                                
          equals space fraction numerator 0.00189 over denominator 143 end fraction space mol space straight L to the power of negative 1 end exponent
          equals space 1.31 space cross times space 10 to the power of negative 5 end exponent space mol space straight L to the power of negative 1 end exponent
    We Know,   AgCl space space rightwards harpoon over leftwards harpoon space space space Ag to the power of plus space plus space Cl to the power of minus
    i.e.  1 mole of AgCl in solution gives 1 mole of  Ag+ ion and 1 mole of Clions. Hence in the solution
                   open square brackets Ag to the power of plus close square brackets space equals space 1.31 space cross times space 10 to the power of negative 5 end exponent space mol space straight L to the power of negative 1 end exponent
open square brackets Cl to the power of minus close square brackets space equals space 1.31 space cross times space 10 to the power of negative 5 end exponent space mol space straight L to the power of negative 1 end exponent
    Applying the law of solubility product, 
             straight K subscript sp space equals space open square brackets Ag to the power of plus close square brackets space open square brackets Cl to the power of minus close square brackets
space space space space space space equals left parenthesis 1.31 space cross times space 10 to the power of negative 5 end exponent right parenthesis thin space left parenthesis 1.31 space cross times space 10 to the power of negative 5 end exponent right parenthesis
space space space space space space equals space 1.7 space cross times space 10 to the power of negative 10 end exponent
    Question 307
    CBSEENCH11006606

    The solubility of CaF2 in water at 298K is 1·7×10–3 gram per 100 cm3. Calculate the solubility product of CaF2 at 298K.

    Solution
    The molecular mass of CaF2
                               equals space 40 plus space 2 space cross times 19 space equals space 78
    Solubility of CaF2 = 1.7 x 10-3 g/100 cm3
                              = 1.7 x 10-2 g L-1

                              equals space fraction numerator 1.7 space cross times 10 to the power of negative 2 end exponent over denominator 78 end fraction mol space straight L to the power of negative 1 end exponent
equals space 2.18 space cross times space 10 to the power of 4 space mol space straight L to the power of negative 1 end exponent
    The solubility equilibrium is
               
     CaF subscript 2 space rightwards harpoon over leftwards harpoon space space space space Ca to the power of 2 plus end exponent space plus space 2 straight F to the power of minus
    i.e. 1 mole of CaF2 in the solution gives 1 mole of Ca2+ ions and 2 moles of F- ions. Hence in the solution.
       open square brackets Ca to the power of 2 plus end exponent close square brackets space equals space 2.18 space cross times space 10 to the power of negative 4 end exponent space mol space straight L to the power of negative 1 end exponent
open square brackets straight F to the power of minus close square brackets space equals space 2 space cross times space left parenthesis 2.18 space cross times space 10 to the power of negative 4 end exponent right parenthesis
space space space space space space space space space equals space 4.36 space cross times space 10 to the power of negative 4 end exponent space mol space straight L to the power of negative 1 end exponent
     Applying the law of solubility product
           straight K subscript sp space equals space open square brackets Ca to the power of 2 plus end exponent close square brackets space space open square brackets straight F to the power of negative 1 end exponent close square brackets squared
space space space space space space space equals space left parenthesis 2.18 space cross times space 10 to the power of negative 4 end exponent right parenthesis thin space left parenthesis 4.36 space cross times space 10 to the power of negative 4 end exponent right parenthesis squared
space space space space space space space equals 4.14 space cross times space 10 to the power of negative 11 end exponent
    Question 309
    CBSEENCH11006608

    Calculate the molar solubility of Ni(OH)2 in 0·10M NaOH. The ionic product of Ni(OH)2 is 2·0 × 10–15.

    Solution
    Let the solubility of Ni(OH)2 in 0·10M NaOH = S mol L–1.
    Ni left parenthesis OH right parenthesis subscript 2 space space space space space space space rightwards harpoon over leftwards harpoon space space space space space Ni to the power of 2 plus end exponent space space space space space plus space space space space space space space space space 2 OH to the power of minus
straight S space space space space space space space space space space space space space space space space space space space space space space space space space straight S space space space space space space space space space space space space space space space space space space space space space left parenthesis 0.10 space plus space 2 straight S right parenthesis

    Applying the law of solubility product
        straight K subscript sp space equals space open square brackets Ni to the power of 2 plus end exponent close square brackets space open square brackets OH to the power of minus close square brackets squared
    or        
      straight K subscript sp space equals space straight S space cross times space left parenthesis 0.10 space plus space 2 straight S right parenthesis squared
    straight i. straight e. space 2.0 space cross times space 10 to the power of negative 15 end exponent space equals space straight S space cross times space left parenthesis 0.10 right parenthesis squared space left square bracket As space 2 straight S less than 0.10 right square bracket
or space space space space space straight S space equals fraction numerator 2.0 space cross times space 10 to the power of negative 15 end exponent over denominator left parenthesis 0.10 right parenthesis squared end fraction
space space space space space space space space space space equals 2.0 space cross times space 10 to the power of negative 13 end exponent mol space straight L to the power of negative 1 end exponent
space space space space space space space space space space equals 2.0 space cross times space 10 to the power of negative 13 end exponent straight M

    Question 310
    CBSEENCH11006609

    At a certain temperature, the solubility product of AgCl is 1 × 10–10, calculate the solubility of AgCl in g/litre.

    Solution

    Let the solubility of AgCl be S mole litre
    AgCl space space space space space space rightwards harpoon over leftwards harpoon space space space space space space space space space space Ag to the power of plus space space space plus space space Cl to the power of minus
straight S space mol space space space space space space space space space space space space space space space space space space straight S space mol space space space space space space space straight S space mol
    Applying the law of solubility product, 
    space space space space space space space straight K subscript ap space equals space open square brackets Ag to the power of plus close square brackets space open square brackets Cl to the power of minus close square brackets space equals space straight S space cross times space straight S
or space space space space straight S squared space equals space straight K subscript sp
or space space space straight S space equals space square root of straight S subscript sp end root space equals space square root of 1 space cross times space 10 to the power of negative 10 end exponent end root
space space space space space space space space equals space 1 cross times space 10 to the power of negative 5 end exponent space mol space straight L to the power of negative 1 end exponent
    Molecular mass of AgCl
                      = 108 + 35.5 = 143.5 
    Hence solubility of AgCl
      = 143.5 x 1 x 10-5 g L-1
      = 14.35 x 10-4 g L-1

    Question 311
    CBSEENCH11006610

    Calculate the solubility of lead iodide in water at 298 K. (Ksp of PbI2 = 7·1×10–9).

    Solution
    Let the solubility of lead iodide in water be S mol L–1.
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#13 {main}</pre>
    i.e. 1 mole of PbI2 in the solution gives 1 mole of Pb2+ ions and 2 moles of I- ions. 
     Hence in the solution open square brackets Pb to the power of 2 plus end exponent close square brackets space equals space straight S space mol space straight L to the power of negative 1 end exponent
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#13 {main}</pre>
    Applying the law of solubility product, 
      space space space space space space straight K subscript sp space equals space open square brackets Pb to the power of 2 plus end exponent close square brackets space open square brackets straight I to the power of minus close square brackets squared space equals space straight S left parenthesis 2 straight S right parenthesis squared space equals space 4 straight S cubed
or space space space space straight S space equals space open parentheses straight K subscript sp over 4 close parentheses to the power of 1 divided by 3 end exponent space equals space open parentheses fraction numerator 7.1 space cross times space 10 to the power of negative 9 end exponent over denominator 4 end fraction close parentheses to the power of 1 divided by 3 end exponent
space space space space space space space space space space space space equals space 1.21 space cross times space 10 to the power of negative 3 end exponent
    Hence solubility of PBI2 in water is 1·21 × 10–3 mol L–1.
    Question 312
    CBSEENCH11006611

    Calculate the concentration of Mg2+ ions and OH- ions in a saturated solution of Mg(OH)2, solubility product of Mg(OH)2 is 9×10–12 

    Solution
    Let the solubility of Mg(OH)2 be S mole per litre.
    Mg left parenthesis OH right parenthesis subscript 2 space space space rightwards harpoon over leftwards harpoon space space space Mg to the power of 2 plus end exponent space plus space 2 OH to the power of minus
    i.e. 1 mole of Mg(OH)2 in the solution gives 1 mole of Mg2+ ions and 2 moles of OH- ions. 
    Hence in the solution,
     
     open square brackets Ag to the power of 2 plus end exponent close square brackets space equals space straight S space mol space straight L to the power of negative 1 end exponent semicolon space space space space open square brackets OH to the power of minus close square brackets space equals space 2 straight S space mol space straight L to the power of negative 1 end exponent
    Applying the law of solubility  product;
            <pre>uncaught exception: <b>Http Error #404</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php line 61<br />#0 [internal function]: com_wiris_plugin_impl_HttpImpl_0(Object(com_wiris_plugin_impl_HttpImpl), NULL, 'http://www.wiri...', 'Http Error #404')
#1 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('com_wiris_plugi...', Array)
#2 [internal function]: _hx_lambda->execute('Http Error #404')
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(532): call_user_func_array(Array, Array)
#4 [internal function]: haxe_Http_5(true, Object(com_wiris_plugin_impl_HttpImpl), Object(com_wiris_plugin_impl_HttpImpl), Array, Object(haxe_io_BytesOutput), true, 'Http Error #404')
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('haxe_Http_5', Array)
#6 [internal function]: _hx_lambda->execute('Http Error #404')
#7 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(27): call_user_func_array(Array, Array)
#8 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(444): com_wiris_plugin_impl_HttpImpl->onError('Http Error #404')
#9 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(458): haxe_Http->customRequest(true, Object(haxe_io_BytesOutput), NULL, NULL)
#10 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(40): haxe_Http->request(true)
#11 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(80): com_wiris_plugin_impl_HttpImpl->request(true)
#12 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#13 {main}</pre>
                         
      = 2 x 1.225 x 10-4 mol ion L-1
      = 2.45 x 10-4 mol ion L-1

    Question 313
    CBSEENCH11006612

    Determine the solubility of silver chromate at 298K. Given that Ksp for Ag2CrO= 1·1 × 10–12. Also determine the molarities of each ion. 

    Solution
    Let the solubility of Ag2CrO4 in water be S mol L–1.
    Ag subscript 2 CrO subscript 4 left parenthesis straight s right parenthesis space space rightwards harpoon over leftwards harpoon space space space space 2 Ag to the power of plus left parenthesis aq right parenthesis space plus space CrO subscript 4 superscript 2 minus end superscript left parenthesis aq right parenthesis
straight i. straight e. space 1 space mole space of space Ag subscript 2 CrO subscript 4 space in space the space solution space gives space
2 space moles space of space Ag to the power of plus space ions space and space 1 space mole space of space CrO subscript 4 superscript 2 minus end superscript space ion.
    Hence in solution, 
    therefore space space open square brackets Ag to the power of plus close square brackets space equals space 2 straight S space mol space straight L to the power of negative 1 end exponent semicolon space space space space open square brackets CrO subscript 4 superscript 2 minus end superscript close square brackets space equals straight S space mol space straight L to the power of negative 1 end exponent
    Applying the law of solubility product
           straight K subscript sp space equals space open square brackets Ag to the power of plus close square brackets squared space open square brackets CrO subscript 4 superscript 2 minus end superscript close square brackets space equals space left parenthesis 2 straight S right parenthesis squared left parenthesis straight S right parenthesis space equals space 4 straight S cubed
or space space space space straight S cubed space equals space straight K subscript sp over 4
or space space space space straight S space equals space open parentheses straight K subscript sp over 4 close parentheses to the power of 1 divided by 3 end exponent space equals space open parentheses fraction numerator 1.1 space cross times space 10 to the power of negative 12 end exponent over denominator 4 end fraction close parentheses to the power of 1 divided by 3 end exponent
space space space space space space space space space space space space space equals space 0.65 space cross times 10 to the power of negative 4 end exponent space mol space straight L to the power of negative 1 end exponent
therefore space space space Molarity space of space Ag to the power of plus space ions
space space space open square brackets Ag to the power of plus close square brackets space equals space 2 straight S space equals space 2 cross times 0.65 space cross times space 10 to the power of negative 4 end exponent
space space space space space space space space space space space space equals 1.03 space cross times space 10 to the power of negative 4 end exponent straight M
    Molarity space fo space CrO subscript 4 superscript 2 minus end superscript space ions comma space
space space space space space open square brackets CrO subscript 4 superscript 2 minus end superscript close square brackets space equals space straight S space equals space 0.65 space cross times space 10 to the power of negative 4 end exponent straight M

    Question 314
    CBSEENCH11006613

    Determine the solubility of barium chromate at 298K. Given K for BaCrO4 = 1·2 × 10–10. Also, determine the molarities of each ion.

    Solution
    Let the solubility of BaCrO4 in water be S mol–1.
    BaCrO subscript 4 left parenthesis straight s right parenthesis space space space space rightwards harpoon over leftwards harpoon space space space space space space Ba to the power of 2 plus end exponent left parenthesis aq right parenthesis space plus space CrO subscript 4 superscript 2 minus end superscript left parenthesis aq right parenthesis
straight i. straight e. space 1 space mole space of space BaCrO subscript 4 space in space the space solution space gives
1 space mole space of space Ba to the power of 2 plus end exponent space ions space and space 1 space mole space of space CrO subscript 4 superscript 2 minus end superscript space ions.
space  
    Hence in solution
    open square brackets Ba to the power of 2 plus end exponent close square brackets space equals space straight S space mol space straight L to the power of negative 1 end exponent semicolon
open square brackets CrO subscript 4 superscript 2 minus end superscript close square brackets space equals space straight S space mol space straight L to the power of negative 1 end exponent
    Applying the law of solubility product,
      <pre>uncaught exception: <b>Http Error #502</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php line 61<br />#0 [internal function]: com_wiris_plugin_impl_HttpImpl_0(Object(com_wiris_plugin_impl_HttpImpl), NULL, 'http://www.wiri...', 'Http Error #502')
#1 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('com_wiris_plugi...', Array)
#2 [internal function]: _hx_lambda->execute('Http Error #502')
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(532): call_user_func_array(Array, Array)
#4 [internal function]: haxe_Http_5(true, Object(com_wiris_plugin_impl_HttpImpl), Object(com_wiris_plugin_impl_HttpImpl), Array, Object(haxe_io_BytesOutput), true, 'Http Error #502')
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('haxe_Http_5', Array)
#6 [internal function]: _hx_lambda->execute('Http Error #502')
#7 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(27): call_user_func_array(Array, Array)
#8 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(444): com_wiris_plugin_impl_HttpImpl->onError('Http Error #502')
#9 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(458): haxe_Http->customRequest(true, Object(haxe_io_BytesOutput), NULL, NULL)
#10 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(40): haxe_Http->request(true)
#11 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(80): com_wiris_plugin_impl_HttpImpl->request(true)
#12 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#13 {main}</pre>
    Question 315
    CBSEENCH11006614
    Question 316
    CBSEENCH11006615

    Determine the solubility of lead chloride at 298K. Given Ksp for PbCl2 = 1·6 × 10–5. Also, determine the molarity of each ion.

    Solution
    Let the solubility of lead chloride in water be S mol L-1
    PbCI subscript 2 left parenthesis straight s right parenthesis space space space rightwards harpoon over leftwards harpoon space space space space Pb to the power of 2 plus end exponent left parenthesis aq right parenthesis space plus space 2 Cl to the power of minus left parenthesis aq right parenthesis
    i.e. 1 mole of PbCI2 in the solution gives 1 mole of Pb2+ ions and 2 moles of Cl- ions. 
    Hence in the solution,
      open square brackets Pb to the power of 2 plus end exponent close square brackets space equals space straight S space mol space straight L to the power of negative 1 end exponent semicolon space space space open square brackets Cl to the power of minus close square brackets space equals space 2 straight S space mol space straight L to the power of negative 1 end exponent
    Applying the law of solubility product
      straight K subscript sp space equals space open square brackets Pb to the power of 2 plus end exponent close square brackets space open square brackets Cl to the power of minus close square brackets squared space equals space straight S space cross times space space left parenthesis 2 straight S right parenthesis squared space equals space 4 straight S cubed
    or space space space straight S space equals space open parentheses straight K subscript sp over 4 close parentheses to the power of 1 divided by 3 end exponent space equals space open parentheses fraction numerator 1.6 space cross times space 10 to the power of negative 5 end exponent over denominator 4 end fraction close parentheses to the power of 1 divided by 3 end exponent
space space space space space space space space equals open parentheses fraction numerator 16 space cross times space 10 to the power of negative 6 end exponent over denominator 4 end fraction close parentheses to the power of 1 divided by 3 end exponent
space space space space space space space equals space left parenthesis 4 space cross times space 10 to the power of negative 6 end exponent right parenthesis to the power of 1 divided by 3 end exponent
space space space space space space space space equals space 1.58 space cross times space 10 to the power of negative 2 end exponent

    Molarity space of space Pb to the power of 2 plus end exponent space ions comma space
open square brackets Pb to the power of 2 plus end exponent close square brackets space equals space straight S space space equals 1.58 space cross times space 10 to the power of negative 2 end exponent straight M
Molarity space of space Cl to the power of minus space ions comma space space open square brackets Cl to the power of minus close square brackets space equals space 2 straight S
space equals space 2 space cross times space 1.58 space cross times space 10 to the power of negative 2 end exponent straight M space equals space 3.16 space cross times space 10 to the power of negative 2 end exponent straight M
    Question 317
    CBSEENCH11006616

    The solubility of Sr(OH)2 at 298K is 19·23g/L of the solution. Calculate the concentration of strontium and hydroxyl ions and pH of the solution. 

    Solution
    Molar mass of Sr(OH)2 = 87·6 + 32 + 2 = 121·6
      Solubility space of space Sr left parenthesis OH right parenthesis subscript 2 space equals space 19.23 space gL to the power of negative 1 end exponent
space space space space space space space space space space space space space space space space space space space space space space space space space space space equals fraction numerator 19.23 over denominator 121.6 end fraction space equals space 0.1581 space mol space straight L to the power of negative 1 end exponent
    The solubility equilibrium is
      Sr left parenthesis OH right parenthesis subscript 2 space space space rightwards harpoon over leftwards harpoon space space space space Sr to the power of 2 plus end exponent space space plus space space 2 OH to the power of minus
    i.e. 1 mole of Sr left parenthesis OH right parenthesis subscript 2 in the solution gives 1 mole of Sr to the power of 2 plus end exponent space ion space and space 2 space moles space of space OH to the power of minus space ions.
    Hence in the solution, 
         open square brackets Sr to the power of 2 plus end exponent close square brackets space equals space 0.581 space mol space straight L to the power of negative 1 end exponent
open square brackets OH to the power of minus close square brackets space equals space 2 space cross times space 0.1581 space space equals space 0.3162 space mol space straight L to the power of negative 1 end exponent
We space know comma
space space space space space space open square brackets straight H to the power of minus close square brackets space open square brackets OH to the power of minus close square brackets space equals space 1 space cross times space 10 to the power of negative 14 end exponent
or space space space space space space space space open square brackets straight H to the power of plus close square brackets space equals space fraction numerator 1 space cross times space 10 to the power of negative 14 end exponent over denominator open square brackets OH to the power of minus close square brackets end fraction space equals fraction numerator 1 space cross times space 10 to the power of negative 14 end exponent over denominator 0.3162 end fraction
space space space space space space space space space space space space space space space space space space space equals space 3.162 space cross times space 10 to the power of negative 4 end exponent space mol space straight L to the power of negative 1 end exponent space
    <pre>uncaught exception: <b>Http Error #404</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php line 61<br />#0 [internal function]: com_wiris_plugin_impl_HttpImpl_0(Object(com_wiris_plugin_impl_HttpImpl), NULL, 'http://www.wiri...', 'Http Error #404')
#1 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('com_wiris_plugi...', Array)
#2 [internal function]: _hx_lambda->execute('Http Error #404')
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(532): call_user_func_array(Array, Array)
#4 [internal function]: haxe_Http_5(true, Object(com_wiris_plugin_impl_HttpImpl), Object(com_wiris_plugin_impl_HttpImpl), Array, Object(haxe_io_BytesOutput), true, 'Http Error #404')
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('haxe_Http_5', Array)
#6 [internal function]: _hx_lambda->execute('Http Error #404')
#7 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(27): call_user_func_array(Array, Array)
#8 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(444): com_wiris_plugin_impl_HttpImpl->onError('Http Error #404')
#9 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(458): haxe_Http->customRequest(true, Object(haxe_io_BytesOutput), NULL, NULL)
#10 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(40): haxe_Http->request(true)
#11 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(80): com_wiris_plugin_impl_HttpImpl->request(true)
#12 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#13 {main}</pre>

    Question 318
    CBSEENCH11006617

    The solubility product of BaSO4 is 1·5 × 10–9. Find solubility in:
    (i) pure water    
    (ii) 0·10 M BaCl
    2.

    Solution
    Let the solubility of BaSO4 be S mole per litre.
    <pre>uncaught exception: <b>Http Error #502</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php line 61<br />#0 [internal function]: com_wiris_plugin_impl_HttpImpl_0(Object(com_wiris_plugin_impl_HttpImpl), NULL, 'http://www.wiri...', 'Http Error #502')
#1 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('com_wiris_plugi...', Array)
#2 [internal function]: _hx_lambda->execute('Http Error #502')
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(532): call_user_func_array(Array, Array)
#4 [internal function]: haxe_Http_5(true, Object(com_wiris_plugin_impl_HttpImpl), Object(com_wiris_plugin_impl_HttpImpl), Array, Object(haxe_io_BytesOutput), true, 'Http Error #502')
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(769): call_user_func_array('haxe_Http_5', Array)
#6 [internal function]: _hx_lambda->execute('Http Error #502')
#7 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(27): call_user_func_array(Array, Array)
#8 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(444): com_wiris_plugin_impl_HttpImpl->onError('Http Error #502')
#9 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/haxe/Http.class.php(458): haxe_Http->customRequest(true, Object(haxe_io_BytesOutput), NULL, NULL)
#10 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/HttpImpl.class.php(40): haxe_Http->request(true)
#11 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(80): com_wiris_plugin_impl_HttpImpl->request(true)
#12 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#13 {main}</pre>
    Applying the law of solubility product, 
          straight K subscript sp space equals space open square brackets Ba to the power of 2 plus end exponent close square brackets space open square brackets SO subscript 4 superscript 2 minus end superscript close square brackets space equals space straight S space cross times space space straight S
or space space straight S squared space equals space straight K subscript sp
or space space space straight S space equals space square root of straight K subscript sp end root space equals space square root of 1.5 space cross times space 10 to the power of negative 9 end exponent end root
space space space space space space space space space space space equals space 3.78 space cross times space 10 to the power of negative 5 end exponent space mol space straight L to the power of negative 1 end exponent

    left parenthesis ii right parenthesis space Solubility space in space 0.10 straight M space BaCl subscript 2 colon
open square brackets Ba to the power of 2 plus end exponent close square brackets space equals space 0.1 space plus space straight S semicolon space open square brackets SO subscript 4 superscript 2 minus end superscript close square brackets space equals space straight S
space space space straight K subscript sp space equals space open square brackets Ba to the power of 2 plus end exponent close square brackets space open square brackets SO subscript 4 superscript 2 minus end superscript close square brackets
space space space space space space space space equals space space left parenthesis 0.1 plus straight S right parenthesis space left parenthesis straight S right parenthesis space equals space 0.1 space straight S space plus space straight S squared
straight S squared space being space the space product space of space two space small space quanitities space is space neglected.
therefore space space space straight K subscript sp space equals space 0.15 space
therefore space space space 0.1 space straight S space equals space 1.5 space cross times space 10 to the power of negative 9 end exponent
or space space space space space straight S space equals space fraction numerator 1.5 space cross times space 10 to the power of negative 9 end exponent over denominator 0.1 end fraction space equals space 1.5 space cross times space 10 to the power of negative 8 end exponent space mol space straight L to the power of negative 1 end exponent
    Question 319
    CBSEENCH11006618

    How many moles of AgBr (Ksp = 5 × 10–13 mol2 L–2) will dissolve in a 0·01 M NaBr solution (NaBr is completely dissociated into Na+ and Br- ion).

    Solution
    The complete ionisation of NaBr is represented as
    NaBr space space space space space space space rightwards arrow space space space space Na to the power of plus space space space space space space plus space space space space Br to the power of minus
0.01 space straight M space space space space space space space space space space space 0.01 space straight M space space space space space space space space space space 0.01 space straight M
therefore space space space open square brackets Br to the power of minus close square brackets space equals space 0.01 space straight M space space
    The solubility equilibrium of AgBr is represented as
         AgBr space space rightwards harpoon over leftwards harpoon space space space Ag to the power of plus space plus space Br to the power of minus
straight K subscript sp space plus space open square brackets Ag to the power of plus close square brackets space open square brackets Br to the power of minus close square brackets
    Now the product of space open square brackets Ag to the power of plus close square brackets space open square brackets Br to the power of minus close square brackets can not exceed 5 x 10-13 mol2  L-2   
    open square brackets Ag to the power of plus close square brackets space equals space fraction numerator 5 space cross times space 10 to the power of negative 13 end exponent over denominator 0.01 end fraction
space space space space space space space space equals space fraction numerator 5 cross times 10 to the power of negative 13 end exponent over denominator 0.01 end fraction cross times 5 space cross times space 10 to the power of negative 11 end exponent space mol space straight L to the power of negative 1 end exponent
    Question 320
    CBSEENCH11006619
    Question 321
    CBSEENCH11006620

    If 20 ml of 1·5 × 10–5 M BaClsolution is mixed with 40 ml of 0·9 × 10–5MNa2SO4 solution, will a precipitate get formed? Ksp for BaSO4 = 0·1 × 10–10.

    Solution

    Solubility product of BaSO4 = 0·1 × 10–10
    Total volume of the mixture solution = 20 + 40 = 60 ml
    (i) Determining Ba2+ ions concentration ; (Before mixing) M1 V1 = M2V2 (After mixing)
               1.5 space cross times space 10 to the power of negative 5 end exponent space cross times space 20 space equals space straight M subscript 2 space cross times space 60
therefore space space space space straight M subscript 2 left parenthesis Molarity space of space BaCl subscript 2 right parenthesis
space space space space equals space fraction numerator 1.5 space cross times space 10 to the power of negative 5 end exponent space cross times space 20 over denominator 60 end fraction equals space 0.5 space cross times space 10 to the power of negative 5 end exponent space mol space straight L to the power of negative 1 end exponent
therefore space space space space open square brackets Ba to the power of 2 plus end exponent close square brackets space space equals space 0.5 space cross times space 10 to the power of negative 5 end exponent space mol space ions space straight L to the power of minus to the power of 1
    left parenthesis ii right parenthesis space Determining space SO subscript 4 superscript 2 minus end superscript space ions space concentration colon
left parenthesis Before space mixing right parenthesis space straight M subscript 1 straight V subscript 1 space equals space straight M subscript 2 straight V subscript 2 left parenthesis After space mixing right parenthesis
space space space space space space space 0.9 space cross times space 10 to the power of negative 5 end exponent space cross times space 40 space equals space straight M subscript 2 space cross times space 60
therefore space space space space straight M subscript 2 left parenthesis Molarity space of space Na subscript 2 SO subscript 4 right parenthesis
space space equals space fraction numerator 0.9 space cross times space 10 to the power of negative 5 end exponent space cross times space 40 over denominator 60 end fraction equals space 0.6 space cross times space 10 to the power of negative 5 end exponent space mol space straight L to the power of negative 1 end exponent
    As sodium sulphate is fully ionised
    space space Na subscript 2 SO subscript 4 space space space rightwards harpoon over leftwards harpoon space space space space 2 Na to the power of 2 plus end exponent space plus space SO subscript 4 superscript 2 minus end superscript
therefore space space open square brackets SO subscript 4 superscript negative 2 end superscript close square brackets space equals space 0.6 space cross times space 10 to the power of negative 5 end exponent space mol space ions space straight L to the power of negative 1 end exponent
    (iii) Determining ionic product;
    open square brackets Ba to the power of 2 plus end exponent close square brackets space open square brackets SO subscript 4 superscript 2 minus end superscript close square brackets space equals space left parenthesis 0.5 space cross times space 10 to the power of negative 5 end exponent right parenthesis thin space left parenthesis 0.6 space cross times space 10 to the power of negative 5 end exponent right parenthesis
space space space space space space space space space space space space space space space space space space space space space space equals space 0.30 space cross times space 10 to the power of negative 10 end exponent
    As the ionic product of BaSO4 (0·30 × 10–10) is more than the Ksp value of the salt, therefore, a precipitate of barium sulphate will be formed.

                      

    Question 322
    CBSEENCH11006621

    If 25.0 cm3 of 0.50 M - Ba(NO3)are mixed with 25·0 cm3 of 0·0220M-NaF, will any BaF2 precipitate  [Ksp of Ba F2 is 1·7 × 10–6 at 298 K.]

    Solution
    Kspof BaF2 = 1·7 × 10–6 Total volume of the mixture solution = 25 + 25 = 50 cm3
    left parenthesis straight i right parenthesis space Determining space of space Ba to the power of 2 plus end exponent space ion space concentration colon
left parenthesis Before space mixing right parenthesis space straight M subscript 1 straight V subscript 1 space equals space straight M subscript 2 straight V subscript 2 space left parenthesis After space mixing right parenthesis
space space space space space space space space space space space 0.05 space cross times space 25 space equals space straight M subscript 2 space cross times space 50
therefore space space space straight M subscript 2 left square bracket Molarity space of space Ba left parenthesis NO subscript 3 right parenthesis subscript 2 right square bracket space equals space fraction numerator 0.05 space cross times space 25 over denominator 50 end fraction space equals space 0.025 space straight M
Since space Ba left parenthesis NO right parenthesis subscript 3 space is space fully space ionised comma space
space space space space space space space space open square brackets Ba to the power of 2 plus end exponent close square brackets space equals space 0.025 space mol space ion space straight L to the power of negative 1 end exponent
    left parenthesis ii right parenthesis space Determining space straight F to the power of minus space ion space concentration colon
left parenthesis Before space mixing right parenthesis space straight M subscript 1 straight V subscript 1 space equals space straight M subscript 2 straight V subscript 2 left parenthesis After space mixing right parenthesis
space space space space space space space space space space space 0.020 space cross times space 25 space space space space equals space straight M subscript 2 space cross times space 50
therefore space space space straight M subscript 2 left parenthesis Molarity space of space NaF right parenthesis space equals fraction numerator 0.020 space cross times space 25 over denominator 50 end fraction equals space 0.01 space straight M
As space NaF space is space fully space ionised
therefore space space space space space space space open square brackets straight F to the power of minus close square brackets space equals space 0.01 space mol space ions space straight L to the power of negative 1 end exponent
    left parenthesis iii right parenthesis space Determining space ionic space product comma space
space space space space BaF subscript 2 space space rightwards harpoon over leftwards harpoon space space space Ba to the power of 2 plus end exponent space plus space 2 straight F to the power of minus
Ionic space product space equals space space open square brackets Ba to the power of 2 plus end exponent close square brackets space open square brackets straight F to the power of minus close square brackets squared
space space space space space space space space space space space space space space space space space space space equals left parenthesis 0.025 right parenthesis thin space left parenthesis 0.01 right parenthesis squared
space space space space space space space space space space space space space space space space space space space equals space 2.5 space cross times space 10 to the power of negative 6 end exponent
because space space Ionic space product space space equals space left parenthesis 2.5 space cross times space 10 to the power of negative 6 end exponent right parenthesis thin space greater than thin space straight K subscript sp space space left parenthesis 1.7 space cross times space 10 to the power of negative 6 end exponent right parenthesis
therefore space space space BaF subscript 2 space will space be space precipitated. space space space space space space space space space space


    Question 323
    CBSEENCH11006622

    Equal volumes of 0.002M solutions of sodium iodate and cupric chlorate are mixed together. Will it lead precipitation of copper iodate? (For cupric iodate Ksp = 7·4 × 10–8).

    Solution
    Solubility equilibrium of copper iodate may be represented as
    Cu left parenthesis IO subscript 3 right parenthesis subscript 2 space space space rightwards harpoon over leftwards harpoon with aq on top space space Cu to the power of 2 plus end exponent left parenthesis aq right parenthesis space plus space 2 IO subscript 3 superscript minus left parenthesis aq right parenthesis
Now comma space space space Cu to the power of 2 plus end exponent semicolon space ions space are space to space be space provided space by space Cu left parenthesis CIO subscript 3 right parenthesis subscript 2 space
and space IO subscript 3 superscript minus space ions space are space to space be space provided space by space
NaIO subscript 3 comma space as space straight a space result space of space dissociation.
space space space space Cu left parenthesis CIO subscript 3 right parenthesis subscript 2 space space rightwards arrow with aq on top space space Cu to the power of 2 plus end exponent left parenthesis aq right parenthesis space plus space 2 CIO subscript 3 superscript minus left parenthesis aq right parenthesis
space space space space space NaIO subscript 3 space rightwards arrow with aq on top space Na to the power of plus left parenthesis aq right parenthesis space plus space IO subscript 3 superscript minus left parenthesis aq right parenthesis
    Since equal volumes of the two solutions have been mixed, therefore, the concentrations of both Cu2+ ions and IO subscript 3 superscript minus ions in the solution after mixing will be reduced to one-half.

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#13 {main}</pre>
    because space space Ionic space product space left parenthesis 0.1 space cross times space 10 to the power of negative 10 end exponent right parenthesis thin space less than thin space straight K subscript sp space left parenthesis 7.4 space cross times space 10 to the power of negative 8 end exponent right parenthesis
therefore space space There space is space no space precipitation.
    Question 324
    CBSEENCH11006623

    What is the maximum concentration of equimolar solutions of ferrous sulphate and sodium sulphide so that when mixed in equal volumes, there is no precipitation of iron sulphide? (For iron sulphide, Ksp = 6·3 × 10–18).

    Solution
    Let the concentration of both FeSO4 and Na2S solutions before mixing = x mol L= xM
    The solubility equilibrium of iron sulphide may be represented as,
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#13 {main}</pre>
    Now, Fe2+ ions are to be provided by FeSOand S2– ions and are to be provided by Na2S, as a result of dissociation.
    FeSO subscript 4 space rightwards arrow with aq on top space Fe to the power of 2 plus end exponent left parenthesis aq right parenthesis space plus space SO subscript 4 superscript 2 minus end superscript left parenthesis aq right parenthesis
Na subscript 2 straight S space rightwards arrow with aq on top space 2 Na to the power of plus left parenthesis aq right parenthesis space plus space straight S to the power of negative 2 end exponent left parenthesis aq right parenthesis
    Since equal volumes of the two solutions have been mixed, the concentration of the solutions as well as of ions on mixing will be reduced to half i.e.
     straight x over 2 straight M
    therefore space space space space Before space mixing comma space open square brackets Fe to the power of 2 plus end exponent close square brackets space equals space xM
space space space space space space After space mixing comma space open square brackets Fe to the power of 2 plus end exponent close square brackets space equals space straight x over 2 straight M
Similarly comma space Before space mixing comma space open square brackets straight S to the power of 2 minus end exponent close square brackets space equals space xM
space space space space space space space space After space mixing comma space space open square brackets straight S to the power of 2 minus end exponent close square brackets space equals space straight x over 2 straight M
Ionic space product space space equals space open square brackets Fe to the power of 2 plus end exponent close square brackets space open square brackets straight S to the power of 2 minus end exponent close square brackets space equals straight x over 2 cross times straight x over 2 space equals straight x squared over 4
    Since oh mixing, there is no precipitation of iron sulphide, therefore,
    Ionic product = Solubility product
    straight x squared over 4 space equals space 6.3 space cross times space 10 to the power of negative 18 end exponent
straight x squared space equals space 4 space cross times space 6.3 space cross times space 10 to the power of negative 18 end exponent space equals space 2.52 space cross times space 10 to the power of negative 18 end exponent
straight x space equals left parenthesis 2.52 space cross times space 10 to the power of negative 18 end exponent right parenthesis to the power of 1 divided by 2 end exponent space equals space 5.02 space cross times space 10 to the power of negative 9 end exponent straight M
    The maximum concentration of both the solutions is 5·02 × 10–9M
    Question 325
    CBSEENCH11006624

    The concentration of sulphide ion in 0·1M HCl solution saturated with hydrogen sulphide is 1·0 × 10–19M. If 10 mL of this solution is added to 5 mL of 0·04M solution of FeSO4, MnCl2, ZnCl2 and CaCl2, in which solutions precipitation will take place? Given Ksp for FeS = 6·3 × 10–18, MnS = 2·5 × 10–13, ZnS =1·6 × 10–24and CdS = 8·0 × 10–27.

    Solution
    Precipitation will occur in the solution for which ionic product is greater than solubility product. As 10 mL of solution containing S2– ion is mixed with 5mL of metal salt solution, therefore,
    After space mixing comma space open square brackets straight S to the power of 2 minus end exponent close square brackets space equals space left parenthesis 1.0 space cross times space 10 to the power of negative 19 end exponent straight M right parenthesis space cross times space fraction numerator left parenthesis 10 space mL right parenthesis over denominator left parenthesis 15 space mL right parenthesis end fraction space
equals space 6.67 space cross times space 10 to the power of negative 20 end exponent straight M

After space mixing comma space open square brackets straight M to the power of 2 plus end exponent close square brackets space equals space left parenthesis 0.04 straight M right parenthesis space cross times space fraction numerator left parenthesis 5 space mL right parenthesis over denominator left parenthesis 15 space mL right parenthesis end fraction space
equals space 1.33 space cross times space 10 to the power of negative 2 end exponent straight M

Ionic space product space space equals space open square brackets straight M to the power of 2 plus end exponent close square brackets space open square brackets straight S to the power of 2 minus end exponent close square brackets

equals space left parenthesis 1.33 space cross times space 10 to the power of negative 2 end exponent right parenthesis space cross times space left parenthesis 6.67 space cross times space 10 to the power of negative 20 end exponent right parenthesis
equals space 8.87 space cross times space 10 to the power of negative 22 end exponent
space space space
    Since the ionic product is greater than the solubility of ZnS and CdS, therefore both ZnCland CdCl2 solutions will be precipitated by passing H2S gas in the presence of HCl.
    Question 326
    CBSEENCH11006625

    The values of Ksp of two sparingly soluble salts Ni(OH)2 and AgCN are 2·0 × 10–15 and 6 × 10–17 respectively. Which salt is more soluble ? Explain

    Solution

    For AgCN
    Let the solubility of AgCN be S1 mol L–1
    AgCN with straight S subscript 1 space mol below space space space rightwards harpoon over leftwards harpoon space space space space space space stack Ag to the power of plus with straight S subscript 1 space mol below space space space plus space space stack CN to the power of minus with straight S subscript 1 space mol below
    Applying the law of solubility product, 
    straight K subscript sp space equals open square brackets Ag to the power of plus close square brackets space open square brackets CN to the power of minus close square brackets space equals space straight S subscript 1 space cross times space straight S subscript 1 space equals space straight S subscript 1 superscript 2
or space space straight S subscript 1 space equals space square root of straight K subscript sp end root
space space space space space space space space space equals square root of 6.0 space cross times space 10 to the power of negative 17 end exponent end root space equals space 7.8 space cross times space 10 to the power of negative 9 end exponent
For space Ni left parenthesis OH right parenthesis subscript 2
Let space the space solubility space of space Ni left parenthesis OH right parenthesis subscript 2 space be space straight S subscript 2 space mol space straight L to the power of negative 1 end exponent
stack Ni left parenthesis OH right parenthesis subscript 2 with straight S subscript 2 space mol below space space space space leftwards harpoon over rightwards harpoon space space space space space stack space Ni to the power of 2 plus end exponent left parenthesis aq right parenthesis with straight S subscript 2 space mol below space space space plus space space stack 2 OH to the power of minus left parenthesis aq right parenthesis with 2 straight S subscript 2 space mol below
space
    Applying the law of solubility product
                straight K subscript sp space equals open square brackets Ni to the power of 2 plus end exponent close square brackets space open square brackets OH to the power of minus close square brackets squared space equals space straight S subscript 2 space cross times space left parenthesis 2 straight S subscript 2 right parenthesis squared space equals space 4 straight S subscript 2 cubed
therefore space space space space straight S subscript 2 cubed space space equals space straight K subscript sp over 4 space equals fraction numerator 2.0 space cross times space 10 to the power of negative 15 end exponent over denominator 4 end fraction
therefore space space space straight S subscript 2 space equals space open square brackets fraction numerator 2.0 space cross times space 10 to the power of negative 15 end exponent over denominator 4 end fraction close square brackets to the power of 1 divided by 3 end exponent space equals space 0.58 space cross times space 10 to the power of negative 4 end exponent
    Since the solubility of Ni(OH) is more than that of AgCN, so Ni(OH)2 is more soluble than AgCN.

    Question 327
    CBSEENCH11006626

    The solubility product constant of Ag2CrO4 and AgBr are 1·1 × 10–12 and 5·0 × 10–13 respectively. Calculate the ratio of the molarities of their saturated solutions.

    Solution
    For Ag2CrO4, the solubility equilibrium is
    Ag subscript 2 CrO subscript 4 space space rightwards harpoon over leftwards harpoon space space space 2 Ag to the power of plus left parenthesis aq right parenthesis space plus space CrO subscript 4 superscript 2 minus end superscript left parenthesis aq right parenthesis
Let space the space solubility space of space Ag subscript 2 CrO subscript 4 space be space straight S space mol space straight L to the power of negative 1 end exponent
therefore space space open square brackets Ag to the power of plus close square brackets space equals space 2 straight S semicolon space space space space open square brackets CrO subscript 4 superscript 2 minus end superscript close square brackets space equals space straight S
space space space space space space straight K subscript sp space equals space open square brackets Ag to the power of plus close square brackets squared space open square brackets CrO subscript 4 superscript minus close square brackets space equals space left parenthesis 2 straight S right parenthesis squared left parenthesis straight S right parenthesis space equals space 4 straight S cubed
or space space space space 4 straight S cubed space equals space straight K subscript sp space space or space space space straight S cubed space equals space straight K subscript sp over 4 space space or space space space straight S space equals space open parentheses straight K subscript sp over 4 close parentheses to the power of 1 divided by 3 end exponent
therefore space space space space straight S space equals space open parentheses fraction numerator 1.1 space cross times space 10 to the power of negative 12 end exponent over denominator 4 end fraction close parentheses to the power of 1 divided by 3 end exponent
space space space space space space space space equals space 0.65 space cross times space 10 to the power of negative 4 end exponent mol space straight L to the power of negative 1 end exponent
    Thus,   straight M subscript Ag subscript 2 CrO subscript 4 end subscript space equals space 0.65 space cross times space 10 to the power of negative 4 end exponent space mol space straight L to the power of negative 1 end exponent
    For AgBr, the solubility equilibrium is
     AgBr space space rightwards harpoon over leftwards harpoon space space space Ag to the power of plus left parenthesis aq right parenthesis space plus space Br to the power of minus left parenthesis aq right parenthesis
    Let the solubility of AgBr be S mol L-1

    therefore space space space space open square brackets Ag to the power of plus close square brackets space equals space straight S space semicolon space space open square brackets Br to the power of minus close square brackets space equals space straight S
space space space space space space space space space space straight K subscript sp space equals space open square brackets Ag to the power of plus close square brackets space open square brackets Br to the power of minus close square brackets space equals space left parenthesis straight S right parenthesis space left parenthesis straight S right parenthesis space equals straight S squared
or space space space space space space space space straight S squared space equals space straight K subscript sp space space end subscript or space space space straight S space equals space left parenthesis straight K subscript sp right parenthesis to the power of 1 divided by 2 end exponent
or space space space space space space space space space straight S space equals space left parenthesis 5.0 space cross times 10 to the power of negative 13 end exponent right parenthesis to the power of 1 divided by 2 end exponent space
space space space space space space space space space space space space space space equals space 0.707 space cross times space 10 to the power of negative 6 end exponent space mol space straight L to the power of negative 1 end exponent
Thus space space space straight M subscript AgBr space equals space 0.707 space cross times space 10 to the power of negative 6 end exponent space mol space straight L to the power of negative 1 end exponent
    The ratio of molarities of their saturated solutions
          equals space straight M subscript Ag subscript 2 CrO subscript 4 end subscript over straight M subscript AgBr space equals space fraction numerator 0.65 space cross times space 10 to the power of negative 4 end exponent over denominator 0.707 space cross times space 10 to the power of negative 6 end exponent end fraction space equals space 91.9

    Since the solubility of Ag2CrO4 is more than that of AgBr, so the former is more soluble.
     
    Question 328
    CBSEENCH11006627

    How do solubility product and ionic product help in predicting the nature of solution? What is the significance of ionic product of water ?

    Solution

    Depending upon the ionic product, the solution of the salt may be unsaturated, saturated or super-saturated.
    (i) If the ionic product < solubility product, the solution is unsaturated.
    (ii) If the ionic product solubility product, the solution is saturated.
    (iii) If the ionic product > solubility product, the solution is super-saturated.

    Question 329
    CBSEENCH11006628

    Flow will you purify an impure sample of sodium chloride containing water soluble impurities?

    Solution
    A saturated solution of the impure sample is prepared and HCl gas is passed through it.

    By passing HCl gas, the concentration of Cl ion increases. According to Le-Chatelier’s principle, equilibrium shifts to the left. As a result, NaCl(s) will be formed. In other words, we can say that pure NaCl will get precipitated leaving behind the impurities in the aqueous solution.
    Question 330
    CBSEENCH11006629

    What is the function of dilute HCl in group II analysis?

    Solution
    The cations of group II are precipitated as their sulphides when H2S gas is passed through their solution acidified with HCl. This is explained oh the basis of common ion effect.

    Due to common ion effect of H+ ions, the degree of dissociation of H2S is suppressed, so the concentration of sulphide ions decreases. Thus the ionic product of sulphides of group II cations (Hg2+, Pb2+, Cu2+, Cd2+, Bi3+) decreases. But this is large enough to exceed the value of their solubility products and radicals of group II get precipitated.

    Other groups cations are not precipitated because their Ksp are comparatively higher.

    Question 331
    CBSEENCH11006630

    What is the function of NH4Cl in group II analysis?

    Solution
    The cations of group III (Al3+, Fe3+, Cr3+, Cr3+ are precipitated as their hydroxides by adding NH4OH to their salt solutions containing NH4Cl. This is explained on the basis of common ion effect.

    Due to the common ion effect of NH subscript 4 superscript plus ions, the degree of dissociation of NH4OH is suppressed, so the concentration of hydroxide ions decreases and thereby the ionic product of the hydroxides of group III cations decreases. Even with their suppressed concentration of OH ions, their ionic products exceed the solubility product and hence radicals of group III get precipitated. The solubility products of hydroxides of higher group cations are relatively high and thus these cations are not precipitated in group III.
    Question 332
    CBSEENCH11006631

    What is the function of ammonium hydroxide in group IV? 

    Solution
    Cations of group IV (Zn2+, Mn2+, Co2+, Ni2+) are precipitated as their sulphides by passing H2S gas through their solution containing NH4OH. This is explained on the basis of common ion effect.
    straight H subscript 2 straight S space space space rightwards harpoon over leftwards harpoon space space space space space 2 straight H to the power of plus space plus space straight S to the power of 2 minus end exponent space space left square bracket Equilibrium space shifts space to space the space right right square bracket
space NH subscript 4 OH space space space rightwards harpoon over leftwards harpoon space space space space space NH subscript 4 superscript plus space plus space OH to the power of minus
    H+ ions react with OH ions to give water Due to decrease in the concentration of H+ions, the equilibrium shifts towards right and S2– ions concentration increases. As a result ionic product increases and becomes sufficient to exceed the solubility products of sulphides of group IV cations. Hence radicals of group IV get precipitated.
    In the absence of NH4OH, the concentration of S2 ions is not sufficient. Hence the sulphides of group IV cations may not get precipitated due to their high Ksp value .
    Question 333
    CBSEENCH11006632

    What is the function of NH4Cl in group V analysis?

    Solution
    Cations of group V (Ba2+, Sr2+, Ca2+) are precipitated as their carbonates on adding ammonium carbonate to their solution containing NH4Cl and NH4OH.

    Due to common ion effect of NH4+ ions, the degree of dissociation of (NH4)2CO3 is suppressed, so the concentration of CO subscript 3 superscript 2 minus end superscript ions decreases. Thus. ionic product of carbonates of group V cations decreases. Even the low concentration of CO subscript 3 superscript 2 minus end superscript ions is sufficient for the ionic product of these ions and cations of the fifth group to exceed the solubility product of corresponding carbonates. Hence, the carbonates of the fifth group get precipitated.

    Other group cations (Na+, K+ and NH4+ ) are either soluble or their solubility product (in the case of Mg2+) is higher.

    Question 334
    CBSEENCH11006633

    What is the necessity of adding NH4OH in group V analysis?

    Solution
    Cations of group V (Ba2+, Sr2+, Ca2+) are precipitated as their carbonates on adding ammonium carbonate to their solutions containing NH4Cl and NH4OH. The necessity of adding ammonium hydroxide arises due to the fact that ammonium carbonate solution usually contains a large amount of ammonium bicarbonate. Since the bicarbonates of Ba2+, Sr2+, Ca2+ are soluble and do not get precipitated, therefore, ammonium hydroxide is added to convert NH4HCO3 into (NH4)2CO3.
    NH subscript 4 HCO subscript 3 space plus space NH subscript 4 OH space space space rightwards arrow space space space left parenthesis NH subscript 4 right parenthesis subscript 2 CO subscript 3 space plus space straight H subscript 2 straight O

    Question 335
    CBSEENCH11006634

    Give reason:  The precipitation of Mg(OH)2 is prevented by the addition of NH4Cl prior to the addition of NH4OH. But its precipitation by NaOH is not prevented by the prior addition of NaCl.

    Solution
    It can be explained by common ion effect.

    Due to common ion effect, NH4ions suppress the ionisation of NH 4OH. The low concentration of OH ions is not sufficient for the ionic product [Mg2+][OH-]2 to exceed the solubility product of Mg(OH)2. Hence it is not precipitated.
    On the other hand, NaOH is a strong base and ionises almost completely. Its dissociation is not much affected by the common ion (Na+) from NaCl. Thus the ionic product [Mg2+][OH]2 exceeds the solubility product value of Mg(OH)2. Hence Mg(OH)2 gets precipitated.

    Question 336
    CBSEENCH11006635

    In which of the following, silver chloride will dissolve more:
    (i) Pure water
    (ii) 0·1M AgNO3 solution?

    Solution
    Silver chloride will be more soluble in water than in AgNO3 solution because, in AgNO3, the solubility of AgCl will be suppressed due to the presence of common Ag+ion.

    Question 338
    CBSEENCH11008062

    For the reaction,

    SO subscript 2 space left parenthesis straight g right parenthesis space plus space 1 half space straight O subscript 2 space left parenthesis straight g right parenthesis space leftwards harpoon over rightwards harpoon space SO subscript 3 space left parenthesis straight g right parenthesis
    if Kp = Kc (RT)x where the symbol has usual meaning then the value of x is (assuming ideality)

    • -1

    • -1/2

    • 1/2

    • 1

    Solution

    B.

    -1/2

    For  the given reaction, ∆ng = np-nR
    where np = number of moles of products
    nR = number of moles of reactants
    Kp = Kc (RT)∆ng
    ∆ng = -1/2

    Question 339
    CBSEENCH11008079

    The species which can best serve as an initiator for the cationic polymerization is

    • LiAlH4

    • HNO3

    • AlCl3

    • BaLi

    Solution

    C.

    AlCl3

    Electron-deficient species (Lewis acid) like AlCl3, BF3, etc, are is used as an initiator for cationic polymerisation.

    Question 344
    CBSEENCH11008102

    In aqueous solution the ionization constants for carbonic acid are
    K1 = 4.2 x 10-7 and K2 = 4.8 x 10-11.
    Select the correct statement for a saturated 0.034 M solution of the carbonic acid.

    • The concentration of CO32- is 0.034 M

    • The concentration of CO32- is greater than that of HCO3-

    • The concentration of H+ and HCO3- are approximately equal

    • The concentration of H+ is double that of CO32-

    Solution

    C.

    The concentration of H+ and HCO3- are approximately equal

    straight H subscript 2 CO subscript 3 space rightwards harpoon over leftwards harpoon with space on top space straight H to the power of plus space plus space HCO subscript 3 superscript minus space semicolon space straight K subscript 1 space equals space 4.2 space straight x space 10 to the power of negative 7 end exponent
HCO subscript 3 superscript minus space rightwards harpoon over leftwards harpoon with space on top space straight H to the power of plus space plus space CO subscript 3 superscript 2 minus end superscript space semicolon space straight K subscript 2 space equals space 4.8 space straight x space 10 to the power of negative 11 end exponent
straight K subscript 1 space greater than greater than space straight K subscript 2
therefore space left square bracket straight H to the power of plus right square bracket space equals space left square bracket HCO subscript 3 superscript minus right square bracket semicolon space straight K subscript 2 space equals space fraction numerator left square bracket straight H to the power of plus right square bracket left square bracket CO subscript 3 superscript 2 minus end superscript right square bracket over denominator left square bracket HCO subscript 3 superscript minus right square bracket end fraction
So comma space left square bracket CO subscript 3 superscript 2 minus end superscript right square bracket space equals space straight K subscript 2 space equals space 4.8 space straight x space 10 to the power of negative 11 end exponent
    Second dissociation constant is much smaller than the first one. Just a small fraction of total HCO3- formed will undergo the second stage of ionization. Hence in a saturated solution.
    Question 345
    CBSEENCH11008103

    The correct order of increasing basicity of the given conjugate bases (R = CH3) is

    • RCO straight O with minus on top space less than space HC space identical to space straight C with minus on top space less than thin space straight N with minus on top straight H subscript 2 space less than straight R with minus on top
    • RCO straight O with minus on top space less than thin space HC space identical to straight C with minus on top space less than space thin space straight R with minus on top less than space straight N with minus on top straight H subscript 2
    • straight R with minus on top space less than HC space identical to space straight C with minus on top space less than space RCO straight O with minus on top space less than space straight N with minus on top straight H subscript 2
    • RCO straight O with minus on top space less than space straight N with minus on top straight H subscript 2 space less than HC space identical to straight C with minus on top space less than thin space straight R with minus on top

    Solution

    A.

    RCO straight O with minus on top space less than space HC space identical to space straight C with minus on top space less than thin space straight N with minus on top straight H subscript 2 space less than straight R with minus on top

    Stronger acid has a weaker conjugate base.
    Order of acidity : RCOOH > CH≡CH > NH3 > RH
    Order of basicity : RCO straight O with minus on top space less than space HC space identical to space straight C with minus on top space less than thin space straight N with minus on top straight H subscript 2 space less than straight R with minus on top 

    Question 347
    CBSEENCH11008110

    pKa of a weak acid (HA) and pKb of a weak base (BOH) are 3.2 and 3.4, respectively. The pH of their salt (AB) solution is

    • 7.2

    • 6.9

    • 7.0

    • 1.0

    Solution

    B.

    6.9

    Given
    pKa (HA) = 3.2
    pKb (BOH) = 3.4
    As given salt is of weak acid and weak base
    therefore,
    pH = 7 + (1/2)pKa - (1/2)pKb
    = 7 + (1/2)(3.2) - (1/2)(3.4)
    = 6.9

    Question 348
    CBSEENCH11008112

    In the following reactions, ZnO is respectively acting as a/an :
    (a) ZnO + Na2O → Na2ZnO2
    (b) ZnO + CO2 → ZnCO3

    • base and acid

    • base and base

    • acid and acid

    • acid and base

    Solution

    D.

    acid and base

    ZnO is amphoteric oxide,in given reaction,
    (a) ZnO + Na2O → Na2ZnO2
    In this reaction ZnO act as Acid.
    (b) ZnO + CO2 → ZnCO3
    In this reaction ZnO act as Base.

    Question 353
    CBSEENCH11008141

    The pKa of a weak acid (HA) is 4.5. The pOH of an aqueous buffered solution of HA in which 50% of the acid is ionized is

    • 4.5

    • 2.5 

    • 9.5

    • 7.0

    Solution

    C.

    9.5

    For buffer solution
    PH space equals space pKa space plus space log space fraction numerator left square bracket salt right square bracket over denominator left square bracket Acid right square bracket end fraction
equals space 4.5 space plus space log space fraction numerator left square bracket salt right square bracket over denominator left square bracket Acid right square bracket end fraction
    as HA is 50% ionized so [Salt] = [Acid]
    pH = 4.5 pH + pOH = 14
    ⇒ pOH = 14 – 4.5 = 9.5

    Question 354
    CBSEENCH11008146

    Regular use of which of the following fertilizers increases the acidity of soil ?

    • Potassium nitrate

    • Urea

    • Superphosphate of lime

    • Ammonium sulphate

    Solution

    D.

    Ammonium sulphate

    (NH4)2 SO4 is a salt of the strong acid and weak base, on hydrolysis it ill produce H+ ion. This will increase the acidity of the soil.
    left parenthesis NH subscript 4 right parenthesis subscript 2 SO subscript 4 space rightwards arrow with space on top space 2 NH subscript 4 superscript plus space plus space SO subscript 4 superscript 2 minus end superscript
NH subscript 4 superscript plus space plus space straight H subscript 2 straight O space rightwards harpoon over leftwards harpoon with space space on top space NH subscript 4 OH space plus straight H to the power of plus

    Question 359
    CBSEENCH11008181

    What is the conjugate base of OH-?

    • O2

    • H2O

    • O-

    • O-2

    Solution

    D.

    O-2

    OH-→ O-2 + H+

    Question 361
    CBSEENCH11008206

    The conjugate base of H2PO4- is

    • PO43-

    • HPO42-

    • H3PO4

    • P2O5

    Solution

    B.

    HPO42-

    H3PO4 is a tribasic acid, thus ionising in three steps.
    left parenthesis straight i right parenthesis space straight H subscript 3 PO subscript 4 space rightwards harpoon over leftwards harpoon with space space on top space straight H to the power of plus space plus space straight H subscript 2 PO subscript 4 superscript minus
left parenthesis ii right parenthesis space straight H subscript 2 PO subscript 4 superscript minus space rightwards harpoon over leftwards harpoon with space on top space straight H to the power of plus space plus space HPO subscript 4 superscript 2 minus end superscript
left parenthesis iii right parenthesis space HPO subscript 4 superscript 2 minus end superscript space rightwards harpoon over leftwards harpoon with space space on top space straight H to the power of plus space plus space PO subscript 4 superscript 3 minus end superscript

    The conjugate base is formed when an acid loses its proton. Thus, HPO42- is the conjugate base of H2PO4- (which is an acid in step II, but is the conjugate base of H3PO4 in step I)
    Question 362
    CBSEENCH11008208

    What is the equilibrium expression for the reaction P4(s) +5O2(g)⇌ P4O10(s)? 

    • Kc = [P4O10] / P4] [O2]5

    • Kc = 1/[O2]5

    • Kc = [O2] 5

    • Kc = [P4O10] / 5[P4][O2]

    Solution

    B.

    Kc = 1/[O2]5

    In the expression for equilibrium constant (Kp or Kc) species  state are not written (i.e., their molar concentrations are not taken as 1)
    P4 (s) + 5O2 (g) ⇌ P4O10 (s)
    Thus, Kc = 1/[O2]5

    Question 363
    CBSEENCH11008209

    For the reaction, CO(g) + Cl2(g) ⇌ COCl2(g) the Kp/Kc is equal to

    • 1/RT

    • 1.0

    • √RT

    • RT

    Solution

    A.

    1/RT

    Kp =Kc (RT)Δn
    Δn = sum of coefficients of gaseous products
    Sum of coefficients of gaseous reactants.
    CO (g) + Cl2 (g) → COCl2 (g)
    Δn = 1-2 = -1
    Kp = Kc (RT)-1
    Kp/Kc = (RT)-1 
    1/RT

    Question 365
    CBSEENCH11008215

    The predominant form of histamine present in human blood is (pKa, Histidine = 6.0)

    Solution

    A.

    The N-atoms present in the ring will have the same pKa values (6.0), while N atom outside the ring will have different pKa value (pKa > 7.4)

    Therefore, two N-atoms inside the ring will remain in the unprotonated form in human blood because of their pKa(6.0) < pH of blood (7.4), while the N-atom outside the ring will remain in protonated form because of its pKa > pH of blood (7.4).

    Question 366
    CBSEENCH11008219

    Which of the following are Lewis acids?

    • BCl3 and AlCl3

    • PH3 and BCl3

    • AlCl3 and SiCl4

    • PH3 and SiCl4

    Solution

    A.

    BCl3 and AlCl3

    Both BCl3 and AlCl3 are Lewis acids as both ‘B’ and ‘Al’ has vacant p-orbitals. SiCl4 is also a Lewis acid as silicon atom has vacant 3d-orbital.

    Question 367
    CBSEENCH11008225

    The addition of a catalyst during a chemical reaction alters which of the following quantities ?

    • Internal energy

    • Enthalpy

    • Activation energy

    • Entropy

    Solution

    C.

    Activation energy

    A catalyst is a substance which alters the reaction but itself remains unchanged in the chemical reaction. In a chemical reaction, it provides a new reaction path by the lowering the activation energy barrier.

    Question 368
    CBSEENCH11008230

    Which one of the following characteristics is associated with adsorption?

    • ΔG, ΔH and  ΔS all are negative

    • ΔG and  ΔH are negative but  ΔS is positive

    • ΔG and  ΔS are negative but  ΔH is positive

    • ΔG is negative but  ΔH and  ΔS are positive

    Solution

    A.

    ΔG, ΔH and  ΔS all are negative

    Adsorption is a spontaneous process that occurs with the release of energy and decrease in the entropy of the substance. For a spontaneous process,  ΔG must be  negative,
     ΔG = ΔH - T ΔS
    As the process is exothermic and randomness of the molecule (entropy) decreases hence both  ΔH and  ΔS will be negative as well.

    Question 370
    CBSEENCH11008234

    Consider the following liquid-vapour equilibrium

    Liquid space rightwards harpoon over leftwards harpoon space Vapour
    Which of the following relations is correct?

    • dlnP over dT equals fraction numerator negative increment H subscript v over denominator R T end fraction
    • dlnP over dT squared space equals space fraction numerator negative increment straight H subscript straight v over denominator straight T squared end fraction
    • dlnP over dT space equals space fraction numerator negative increment straight H subscript straight v over denominator RT squared end fraction
    • dlnG over dT space equals space fraction numerator negative increment straight H subscript straight v over denominator RT squared end fraction

    Solution

    C.

    dlnP over dT space equals space fraction numerator negative increment straight H subscript straight v over denominator RT squared end fraction

    The given phase equilibria is 
    Liquid space rightwards harpoon over leftwards harpoon space Vapour
    This equilibrium states that, when liquid is heated, it converts into vapour but on cooling, it further converts into liquid, which is derived by Clausius clapeyron and the relationship is written as,

    dlnP over dT space equals space fraction numerator negative increment straight H subscript straight v over denominator RT squared end fraction
where space increment straight H subscript straight v space equals space Heat space of space vaporisation

    Question 372
    CBSEENCH11008260

    Which of these is least likely to act as a lewis base? 

    • CO

    • F-

    • BF3

    • PF3

    Solution

    C.

    BF3

    Electron rich species are called lewis base. Among the given, BF3 is an electron deficient species, so have a capacity of electrons accepting instead of donating that's why it is least likely to act as a lewis base. It is a lewis acid. 

    Question 373
    CBSEENCH11008267

    pH of a saturated solution of Ba(OH)2 is 12. The value of solubility product Ksp of Ba(OH)2 is

    • 3.3 x 10-7

    • 5.0 x 10-7

    • 4.0 x 10-6

    • 5.0 x 10-6

    Solution

    B.

    5.0 x 10-7

    Given, pH of Ba(OH)2 = 12
    pOH = 14-pH
    = 14-12 = 2
    We know that,
    pOH = -log [OH-]
    2 =-log [OH-]
    [OH-] = antilog (-2)
    [OH-] = 1 x 10-2
    Ba(OH)2dissolves in water as 
    stack Ba left parenthesis OH right parenthesis subscript 2 space left parenthesis straight s right parenthesis with straight s space mol space straight L to the power of negative 1 end exponent below space rightwards harpoon over leftwards harpoon space stack Ba to the power of 2 plus end exponent with straight s below space plus stack 2 OH to the power of minus with 2 straight s below
left square bracket OH to the power of minus right square bracket space equals space 2 straight s space equals space 1 space straight x space 10 to the power of negative 2 end exponent
left square bracket Ba to the power of 2 plus end exponent right square bracket space equals space fraction numerator left square bracket OH to the power of minus right square bracket over denominator 2 end fraction space equals space fraction numerator 1 space straight x space 10 to the power of negative 2 end exponent over denominator 2 end fraction
straight K subscript sp space equals space left square bracket Ba to the power of 2 plus end exponent right square bracket left square bracket OH to the power of minus right square bracket squared
space equals space open parentheses fraction numerator 1 space straight x space 10 to the power of negative 2 end exponent over denominator 2 end fraction close parentheses left parenthesis 1 straight x 10 to the power of negative 2 end exponent right parenthesis squared
space equals space 0.5 space straight x space 10 to the power of negative 6 end exponent space equals space 5 space straight x space 10 to the power of negative 7 end exponent

    Question 374
    CBSEENCH11008271

    Equimolar solutions of the following substances were prepared separately, which one of these will record the highest pH value?

    • BaCl2

    • AlCl3

    • LiCl

    • BeCl2

    Solution

    A.

    BaCl2

    BaCl2 is a salt of strong acid HCl and strong base Ba(OH)2. So, its aqueous solution is neutral with pH 7. All other salts give acidic solution due to cationic hydrolysis, so their pH is less than 7. Thus, pH value is highest for the solution of BaCl2.

    Question 375
    CBSEENCH11008275

    Buffer solutions have constant acidity and alkalinity because

    • these give unionised acid or base on reaction with added acid or alkali

    • acids and alkalies in these solutions are shielded from attack by other ions.

    • they have a large excess of H+ or OH- ions

    • they have fixed value of pH

    Solution

    A.

    these give unionised acid or base on reaction with added acid or alkali

    If a small amount of an acid or alkali is added to a buffer solution, it converts them into unionised acid or base. Thus, remains unaffected or in other words its acidity/alkalinity remains constant. e.g.,
    H3O+ + A-  ⇌ H2O +HA
    -OH +HA → H2O +A-
    If acid is added, it reacts with A- to form undissociated HA. Similarly, if base/alkali is added, O H- combines with HA to give H2O and A- and thus, maintains the acidity/alkalinity of buffer solution.

    Question 378
    CBSEENCH11008311

    The value of ΔH for the reaction

    X2 (g) + 4Y2 (g) ⇌ 2XY4 (g) is less than zero. Formation of XY4 (g) will be favoured at

    • Low pressure and low temperature

    • high temperature and low pressure

    • high pressure and low temperature

    • high temperature and high pressure

    Solution

    C.

    high pressure and low temperature

    X2 (g) + 4Y2 (g) ⇌ 2XY4 (g);


    ΔH < 0 and Δn < 0
    Therefore, the forward reaction is favoured at high pressure and low temperature. (According to Le- Chatelier's principle)
    Question 379
    CBSEENCH11008312

    For the reaction N2 (g) + O2 (g) ⇌  2NO (g), the equilibrium constant is K1. The equilibrium constant is K2 for the reaction 2NO (g) + O2(g) ⇌ 2NO2 (g). What is K for the reaction NO subscript 2 space left parenthesis straight g right parenthesis space rightwards harpoon over leftwards harpoon 1 half straight N subscript 2 space left parenthesis straight g right parenthesis space plus straight O subscript 2 space left parenthesis straight g right parenthesis ? space space

    • 1/(4K1K2)

    • [1/K1K2]1/2

    • 1/(K1K2)

    • 1/(2K1K2)

    Solution

    B.

    [1/K1K2]1/2

    N2 (g) + O2 (g) ⇌  2NO (g) ; K1 (i)
    2NO (g) + O2 (g) ⇌ 2NO2 (g) ; K2 (ii)
    ______________________________
    N2 (g) + O2(g)  ⇌ 2NO2 (g) ; K = K1 x K2
    therefore, For NO2 (g) = N2/2 (g)  +O2 (g);
    K = [1/K1K2]1/2

    Question 380
    CBSEENCH11008324

    What is the pH of the resulting solution when equal volumes of 0.1 M NaOH and 0.01 M HCl are mixed?

    • 12.65

    • 2.0

    • 7.0

    • 1.04

    Solution

    A.

    12.65

    When equal volumes of acid and base are mixed then resulting solution become alkaline if the concentration of base is taken high.
    Let normality  of the solution after mixing 0.1 M
    NaOH and 0.01 M HCl is N.
    therefore,   N1V1 - N2V2 = NV
    or   0.1 x 1 - 0.01 x 1 = N x 2
    Since normality, of NaOH, is more than that of HCl. Hence, the resulting solution is alkaline.
    Or
    [OH-] = N = 0.09/2 = 0.045 N
    Or pOH = - log (0.045) = 1.35
    therefore, pH = 14-pOH
    = 14 - 1.35 = 12.65

    Question 381
    CBSEENCH11008327

    Which one of the following pairs of the solution is not an acidic buffer?

    • HClO4 and NaClO4

    • CH3COOH and CH3COONa

    • H2CO3 and Na2PO4

    • H2PO4 and Na3PO4

    Solution

    A.

    HClO4 and NaClO4

    A buffer solution is one which resists changes in pH when small quantities of an acid or an alkali are added to it.

    HClO4 and NaClO4 are not an acidic buffer because strong acid with its salt cannot form buffer solution.
    Question 382
    CBSEENCH11008333

    If the equilibrium constant for 

    straight N subscript 2 space left parenthesis straight g right parenthesis space plus space straight O subscript 2 space left parenthesis straight g right parenthesis space rightwards harpoon over leftwards harpoon space 2 space NO space left parenthesis straight g right parenthesis space is space straight K comma space the space equilibrium space constant space for
1 half straight N subscript 2 space left parenthesis straight g right parenthesis space plus space 1 half straight O subscript 2 left parenthesis straight g right parenthesis space rightwards harpoon over leftwards harpoon space NO space left parenthesis straight g right parenthesis space will space be

    • K1/2

    • K/2

    • K2

    Solution

    A.

    K1/2

    As we can see the reaction for which we have to find out equilibrium constant is different only in stoichiometric coefficient as compared to the given reaction. Hence, we can find equilibrium constant as,
    straight N subscript 2 space left parenthesis straight g right parenthesis space plus space straight O subscript 2 space left parenthesis straight g right parenthesis space rightwards harpoon over leftwards harpoon space 2 space NO space left parenthesis straight g right parenthesis thin space is space straight K
straight i. straight e. space straight K space equals space fraction numerator left square bracket NO right square bracket squared over denominator left square bracket straight N subscript 2 right square bracket left square bracket straight O subscript 2 right square bracket end fraction space space space.. space left parenthesis straight i right parenthesis
Let space equilibrium space constant space for space the space reaction comma
1 half space straight N subscript 2 space left parenthesis straight g right parenthesis space plus space 1 half straight O subscript 2 space left parenthesis straight g right parenthesis space rightwards harpoon over leftwards harpoon space 2 NO space left parenthesis straight g right parenthesis space is space straight K apostrophe
straight i. straight e space space straight K apostrophe space equals space fraction numerator left square bracket NO right square bracket over denominator left square bracket straight N subscript 2 right square bracket to the power of 1 divided by 2 end exponent left square bracket straight O subscript 2 right square bracket to the power of 1 divided by 2 end exponent end fraction
On space squaring space both space sides
straight K apostrophe squared space equals space fraction numerator left square bracket NO right square bracket squared over denominator left square bracket straight N subscript 2 right square bracket left square bracket straight O subscript 2 right square bracket end fraction space space.. space left parenthesis ii right parenthesis
On space comparing space Eqs. space left parenthesis straight i right parenthesis space and space left parenthesis ii right parenthesis space we space get
straight K equals space straight K apostrophe squared
or
straight K to the power of apostrophe space equals space square root of straight K

    Question 383
    CBSEENCH11008334

    An aqueous solution of which of the following compounds is the best conductor of electric current?

    • Acetic acid C2H4O2

    • Hydrochloric acid, HCl

    • Ammonia, NH3

    • Fructose, C6H12O6

    Solution

    B.

    Hydrochloric acid, HCl

    HCl is strong acid and dissociates completely. Hence, it conducts electricity best in its aqueous solution.

    Question 384
    CBSEENCH11008349

    If pH ofa saturated solution of Ba(OH)2 is 12, the value of its Ksp is 

    • 4.00 x 10-6 M3

    • 4.00 x 10-7 M3

    • 5.00 x 10-6 M3

    • 5.00 x 10-7 M3

    Solution

    C.

    5.00 x 10-6 M3

    Given pH of Ba(OH)2 = 12
    therefore, [H+] = [1 x 10-12]
    and [OH-] = 1 x 10-14 / 1 x 10-12   {[H+][OH-] = 1 x 10-14}
    Ba left parenthesis OH right parenthesis subscript 2 space equals space stack Ba to the power of 2 plus end exponent space with straight s below plus space stack 2 OH to the power of minus with 2 straight s below
Ksp space equals space left square bracket Ba to the power of 2 plus end exponent right square bracket left square bracket OH to the power of minus right square bracket squared
space equals space left square bracket straight s right square bracket left square bracket 2 straight s squared right square bracket

equals space open square brackets fraction numerator 1 space straight x space 10 to the power of negative 2 end exponent over denominator 2 end fraction close square brackets left parenthesis 1 space straight x space 10 to the power of negative 2 end exponent right parenthesis squared

equals space 0.5 space straight x space 10 to the power of negative 6 end exponent space equals space 5.0 space straight x space 10 to the power of negative 7 end exponent space straight M cubed

    Question 385
    CBSEENCH11008361

    What is [H+] in mol/L of a solution that is 0.20 M in CH3COONa and 0.10 M in CH3COOH? 
    (Ka for CH3COOH = 1.8 x 10-5 )

    • 3.5 x 10-4

    • 1.1 x 10-5

    • 1.8 x 10-5

    • 9.0 x 10-6

    Solution

    D.

    9.0 x 10-6

    CH3COOH (weaK acid) and CH3COONa (conjugated salt) form acidic buffer and for acidic buffer,
    pH space equals space pK subscript straight a space plus space log space fraction numerator open square brackets salt close square brackets over denominator left square bracket acid right square bracket end fraction
and
left square bracket straight H to the power of plus right square bracket space equals space minus space antilog space pH
pH space equals space minus space log space straight K subscript straight a space plus space log space fraction numerator left square bracket salt right square bracket over denominator left square bracket acid right square bracket end fraction space space space space space left square bracket therefore space pK subscript straight a space equals space minus space log space straight K subscript straight a right square bracket
space equals space minus log space left parenthesis 1.8 space straight x space 10 to the power of negative 5 end exponent right parenthesis space plus space log space fraction numerator 0.20 over denominator 0.10 end fraction
equals space 4.74 space plus space log space 2
equals space 4.74 space plus space 0.3010 space equals space 5.041
Now comma space left square bracket straight H to the power of plus right square bracket space equals antilog space left parenthesis negative 5.045 right parenthesis
equals space 9.0 space straight x space 10 to the power of negative 6 end exponent space mol divided by straight L

    Question 386
    CBSEENCH11008362

    In which of the following equilibrium Kc and Kp are not equal?

    • 2NO (g) ⇌ N2 (g)  + O2 (g)

    • SO2 (g) + NO2 (g) ⇌ SO3 (g) + NO (g)

    • H2 (g) + I2 (g) ⇌ 2 HI (g)

    • 2C (s) + O2 (g) ⇌ 2CO2 (g)

    Solution

    D.

    2C (s) + O2 (g) ⇌ 2CO2 (g)

    The reaction for which the number of moles of gaseous products (np) is not equal to the number of moles of gaseous reactants (nR), has a different value of Kc and Kp.
    a) np = nR = 2 thus, Kp = Kc
    b) np = nR = 2 thus, Kp = Kc
    c) np = nR = 2 thus, Kp = Kc
    d) np = 2, nR = 1 thus, Kp not equal to Kc

    Question 389
    CBSEENCH11008377

    Which of the following molecules acts as a Lewis acid?

    • (CH)3B

    • (CH3)O

    • (CH3)P

    • (CH3)2)O

    Solution

    A.

    (CH)3B

    According to Lewis concept " Acids are electron acceptor and bases are electron donor" Since, electron deficient compounds also have an ability to accept electrons, these are regarded as acids.
    Trimethylborane (CH)3B have incomplete octet thus, act as Lewis acid.

    Question 390
    CBSEENCH11008380

    The ionisation constant of ammonium hydroxide is 1.77 x 10-5 at 298 K. Hydrolysis constant of ammonium chloride is 

    • 5.65 x 10-10

    • 6.50 x 10-12

    • 5.65 x 10-13

    • 5.65 x 10-12

    Solution

    A.

    5.65 x 10-10

    Given comma space straight K subscript straight a space left parenthesis NH subscript 4 OH right parenthesis space equals space 1.77 space straight x space 10 to the power of negative 5 end exponent

NH subscript 4 OH space leftwards harpoon over rightwards harpoon space NH subscript 4 to the power of plus space plus space OH to the power of minus

straight K subscript straight a space equals space fraction numerator left square bracket NH to the power of plus subscript 4 right square bracket left square bracket OH to the power of minus right square bracket over denominator left square bracket NH subscript 4 OH right square bracket end fraction space equals space 1.77 space straight x space 10 to the power of negative 5 end exponent space... space left parenthesis straight i right parenthesis
    Hydrolysis of NH4Cl takes place as,
    NH4Cl + H2O → NH4OH + HCl
    or 
    NH4+ +H2O → NH4OH + H+
    Hydrolysis constant, Kh

    straight K subscript straight h space equals space fraction numerator left square bracket NH subscript 4 OH right square bracket left square bracket straight H to the power of plus right square bracket over denominator left square bracket NH subscript 4 to the power of plus right square bracket end fraction space... space left parenthesis ii right parenthesis

or space straight K subscript straight h space equals space fraction numerator left square bracket NH subscript 4 OH to the power of plus right square bracket left square bracket OH to the power of minus right square bracket over denominator left square bracket NH subscript 4 to the power of plus right square bracket left square bracket OH to the power of minus right square bracket end fraction space... space left parenthesis iii right parenthesis

from space eqs. space left parenthesis straight i right parenthesis space and space left parenthesis iii right parenthesis

straight K subscript straight h space equals space straight K subscript straight w over straight K subscript straight a space left square bracket space because space left square bracket OH to the power of minus right square bracket left square bracket straight H to the power of plus right square bracket space equals space straight K subscript straight w right square bracket
equals space fraction numerator 10 to the power of negative 14 end exponent over denominator 1.77 space straight x space 10 to the power of negative 5 end exponent end fraction
space equals space 5.65 space straight x space 10 to the power of minus to the power of 10
    Question 391
    CBSEENCH11008387

    Nitrobenzene can be prepared from benzene by using a mixture of conc. HNO3 and Conc. H2SO4.In the mixture, nitric acid acts as a/an:

    • reducing agent

    • acid

    • base

    • catalyst

    Solution

    C.

    base

    Proton donor is acids and proton acceptor is bases.
    Conc. H2SO4 and conc. HNO3 react in the following manner:
    HNO3 + H2SO4 → H2NO3+ +HSO4-
    H2NO3+ → NO2+ +H2O
    Hence, in this reaction HNO3 acts as a base and H2SO4 as an acid.

    Question 393
    CBSEENCH11008396

    Equal volumes of three acid solutions of pH 3.4 and 5 are mixed in a vessel. What will be the H+ ion concentration in the mixture?

    • 1.11 x 10-4 M

    • 3.7 x 10-4

    • 3.7 x 10-3 M

    • 1.11 x 10-3 M

    Solution

    B.

    3.7 x 10-4

    [H]+ in mixture
    [H]+ of 1st acid x its volume + [H+]
    of IInd acid  x its volume + [H+] of 

    equals fraction numerator IIIrd space acid space straight x space its space volume over denominator Total space volume end fraction

straight M space equals fraction numerator straight M subscript 1 straight V subscript 1 space plus straight M subscript 2 straight V subscript 2 space plus space straight M subscript 3 straight V subscript 3 over denominator straight V end fraction
    Assume the volume of each solution is 1 L.
    [H3O+] in solution of pH = 3 is 10-3M
    [H3O+] in solution of pH = 4 is 10-4 M
    [H3O+] in solution is pH is 5 is 10-5 M
    Total space left square bracket straight H subscript 3 straight O to the power of plus right square bracket space equals space space fraction numerator 10 to the power of negative 3 end exponent space plus 10 to the power of negative 4 end exponent plus 10 to the power of negative 5 end exponent over denominator space 3 end fraction
space equals space 0.00037
equals 3.7 space straight x space 10 to the power of negative 4 end exponent space straight M

    Question 394
    CBSEENCH11008405

    If the concentration of OH- ions in the reaction Fe(OH)3 (s)  ⇌ Fe3+ (aq) + 3OH-(aq) is decreased by 1/4 times, then equilibrium concentration of Fe3+ will increase by 

    • 8 times

    • 16 times

    • 64 times

    • 4 times

    Solution

    C.

    64 times

    The concentration of solids taken to be unity.
    Fe(OH)3 (s)  ⇌ Fe3+ (aq) + 3OH- (aq)
    therefore,
    K = [Fe3+][OH-]3
    Hence, if OH- ion concentration is decreased by 1/4 times. then equilibrium concentration of Fe3+ will increase by 64 times.

    Question 395
    CBSEENCH11008408

    Base strength of 

    1. space straight H subscript 3 straight C straight C with minus on top straight H subscript 2
2. space straight H subscript 2 straight C equals straight C with minus on top straight H
3. space straight H minus space straight C identical to straight C with minus on top

    is in the order of 

    • (2) > (1) > (3)

    • (3) > (2) > (1) 

    • (1) > (3)> (2) 

    • (1) > (2) > (3)

    Solution

    D.

    (1) > (2) > (3)

    Stronger the acid, weaker is its conjugate base. 
    The strength of their conjugate acids are in the order: 
    HC space identical to CH space greater than thin space straight H subscript 2 straight C space equals CH subscript 2 space greater than thin space CH subscript 3 minus CH subscript 3
    Therefore, the correct order of strength of their conjugate base is: 
    CH subscript 3 CH subscript 2 to the power of minus greater than thin space straight H subscript 2 straight C space equals straight C to the power of minus straight H space greater than thin space HC identical to straight C to the power of minus

    Question 396
    CBSEENCH11008410

    Equimolar solutions of the following  were prepared in water separately which one of the solutions will record the highest pH? 

    • SrCl2

    • BaCl2

    • MgCl2

    • CaCl2

    Solution

    B.

    BaCl2

    As the basic nature increases
    pH  of base > 7
    pH of acid < 7
    In alkaline earth metals on moving downward the size of cation increases, thus basicity increases. Hence, the increasing order or basicity is as:
    MgCl2 < CaCl2 < SnCl2< BaCl2
    Therefore, the solution of BaCl2 will record the highest pH.

    Question 397
    CBSEENCH11008418

    The dissociation equilibrium  of gas AB2 can be represented as

    2AB2 (g) ⇌ 2AB (g) + B2 (g)
    The degree of dissociation is 'x' and is small compared to 1. The expression relating the degree of dissociation  (x) with equilibrium constant Kp and total pressure p is 

    • (2Kp / p)

    • (2Kp/p)1/3

    • (2Kp/p)1/2

    • (Kp/p)

    Solution

    D.

    (Kp/p)

    Initial              1                   0               0
    at equ        2(1-x)              2x               x
    where,  x = degree of dissociation
    Total moles at equilibrium = 2-2x + 2x + x
     = ( 2 + x)
    straight p subscript AB subscript 2 end subscript space equals space fraction numerator 2 space left parenthesis 1 minus straight x right parenthesis straight p over denominator left parenthesis 2 plus straight x right parenthesis end fraction
straight p subscript AB space equals space fraction numerator 2 xp over denominator left parenthesis space 2 space plus straight x right parenthesis end fraction
straight p subscript straight B subscript 2 space end subscript space equals space fraction numerator xp over denominator space left parenthesis space 2 space plus straight x right parenthesis end fraction
straight K subscript straight p space equals space fraction numerator left parenthesis straight p subscript AB right parenthesis squared left parenthesis straight p subscript straight B subscript 2 right parenthesis over denominator left parenthesis straight p subscript AB subscript 2 end subscript right parenthesis end fraction
space equals space fraction numerator open parentheses begin display style fraction numerator 2 xp over denominator 2 plus straight x end fraction end style close parentheses squared open parentheses begin display style fraction numerator straight x over denominator 2 space plus straight x end fraction end style straight p close parentheses over denominator open parentheses begin display style fraction numerator 2 left parenthesis 1 minus straight x right parenthesis over denominator 2 plus straight x end fraction end style straight p close parentheses end fraction
equals space fraction numerator straight x cubed straight p over denominator left parenthesis 2 plus straight x right parenthesis left parenthesis 1 minus straight x right parenthesis squared end fraction
open square brackets therefore space straight x less than less than less than space 1 space and space 2 space so comma space left parenthesis 1 minus straight x right parenthesis space almost equal to 1 comma space left parenthesis 2 plus straight x right parenthesis space almost equal to space 2 close square brackets
equals fraction numerator straight x cubed straight p over denominator 2 end fraction
straight x space equals open parentheses fraction numerator 2 straight K subscript straight p over denominator straight p end fraction close parentheses to the power of 1 divided by 3 end exponent

    Question 398
    CBSEENCH11008420

    The value of KP1 and Kp2 for the reactions

    X ⇌ Y +Z  ... (i)
    A ⇌ 2B    ... (ii)

    are in the ratio of 9:1. if the degree of dissociation of X and A be equal, then the total pressure at equilibrium (i) and (ii) are in the ratio

    • 3:1

    • 1:9

    • 36:1

    • 1:1

    Solution

    C.

    36:1

    From equation.
    X     ⇌    Y  +   Z
    1            0        0     initial mole
    (1-α)     α         α     mole at equilibrium

    K subscript p subscript 1 space end subscript space equals space fraction numerator p subscript y italic space x italic space p subscript z over denominator straight p subscript straight x end fraction
equals fraction numerator open square brackets begin display style fraction numerator straight alpha space plus straight p subscript 1 over denominator 1 plus straight alpha end fraction end style close square brackets squared over denominator open square brackets begin display style fraction numerator 1 minus straight alpha over denominator 1 plus straight alpha end fraction end style close square brackets straight p subscript 1 end fraction
K subscript p subscript 1 space end subscript space equals space fraction numerator alpha squared p subscript 1 over denominator 1 minus alpha squared end fraction space... space left parenthesis straight i right parenthesis
From space equation
straight A space space space space space space space space leftwards harpoon over rightwards harpoon space space space space space space 2 straight B
1 space space space space space space space space space space space space space space space space space space space 0 space space space space space space space Initial space mole
left parenthesis 1 minus straight alpha right parenthesis space space space space space space space space space space 2 straight alpha space space space space space space mole space at space equilibrium

straight k subscript straight p subscript 2 end subscript equals fraction numerator open square brackets begin display style fraction numerator 2 straight alpha space over denominator 1 plus straight alpha end fraction. straight p subscript 2 end style close square brackets squared over denominator open square brackets begin display style fraction numerator 1 minus straight alpha over denominator 1 plus straight alpha end fraction end style close square brackets straight p subscript 2 end fraction

K subscript p subscript 1 space end subscript space equals space fraction numerator italic 4 alpha squared p italic 2 over denominator 1 minus alpha squared end fraction space.. space left parenthesis ii right parenthesis
From space eqa space left parenthesis straight i thin space right parenthesis and space left parenthesis ii right parenthesis
straight K subscript straight p subscript 1 end subscript over straight K subscript straight p subscript 2 end subscript space equals space fraction numerator straight p subscript 1 over denominator 4 straight p subscript 2 end fraction
equals space 9 over 1 space equals space fraction numerator straight p subscript 1 over denominator 4 straight p subscript 2 end fraction
rightwards double arrow space straight p subscript 1 over straight p subscript 2 space equals space 36 over 1

    Question 400
    CBSEENCH11008422

    Calculate the pOH of a solution at 250C that contains 1 x 10-10 M of hydronium ions.

    • 7

    • 4

    • 9

    • 1

    Solution

    B.

    4

    [H3O+] = [H+] = 10-10

    pH + pOH = [14]
    pH = - log [ H+]
    pH = - log [10-10]
    pH = 10
    ⇒ pOH + 10 = 14
    ⇒ pOH = 14-10 = 4

    Question 403
    CBSEENCH11008436

    Identify the correct statement for the change of Gibbs energy for a system (ΔGsystem) at constant temperature and pressure

    • If ΔGsystem > 0, the process is spontaneous

    • If ΔGsystem =0, the system has attained equilibrium

    • If ΔGsystem < 0, the system is still moving in a particular direction

    • If ΔGsystem < 0, the process is not spontaneous

    Solution

    B.

    If ΔGsystem =0, the system has attained equilibrium

    If the Gibbs free energy for a system (ΔGsystem) is equal to zero, then system is present in equilibrium at a constant temperature and pressure.

    Question 404
    CBSEENCH11008439

    The enthalpy and entropy change for the reaction:

    Br2 (l) + Cl2 (g)→ 2BrCl (g)

    are 30 kJ mol-1 and 105 JK-1 mol-1 respectively. The temperature at which the reaction will be in equilibrium is:

    • 285.7 K 

    • 273 K

    • 450 K

    • 300 K

    Solution

    A.

    285.7 K 

    At equilibrium, Gibbs free energy change (ΔGo) is equal to zero. The following thermodynamic relation is used to show the relation of ΔGo with the enthalpy change (ΔHo) and entropy change (ΔSo)
    ΔGo  = ΔHo - ΔSo
    0 = 30 x 103 (J mol-1) - T x 105 (J K-1) mol-1
    Therefore comma
straight T space equals space fraction numerator 30 space straight x space 10 cubed over denominator 105 end fraction space straight K thin space equals space space 285.71 space straight K

    Question 405
    CBSEENCH11008441

    For the reaction,

    CH4  (g) + 2 O2 (g) ⇌ CO2 (g) + 2H2O (l), 

    ΔrH = - 170. 8 kJ mol-1

    Which of the following statements is not true? 

    • At equilibrium, the concentrations of CO2 (g) and H2O (l) are not equal

    • The equilibrium constant for the reaction is given by Kpfraction numerator left square bracket CO subscript 2 right square bracket over denominator left square bracket CH subscript 4 right square bracket left square bracket straight O subscript 2 right square bracket end fraction

    • Addition of CH4 (g) or O2 (g) at equilibrium will cause a shift to the right

    • The reaction is exothermic

    Solution

    B.

    The equilibrium constant for the reaction is given by Kpfraction numerator left square bracket CO subscript 2 right square bracket over denominator left square bracket CH subscript 4 right square bracket left square bracket straight O subscript 2 right square bracket end fraction

    For the reaction,
    CH4  (g) + 2 O2 (g) ⇌ CO2 (g) + 2H2O (l), 
    ΔrH = - 170. 8 kJ mol-1
    This equilibrium is an example of heterogeneous chemical equilibrium.Hence, for it
    straight K subscript straight c space equals space fraction numerator left square bracket CO subscript 2 right square bracket over denominator left square bracket CH subscript 4 right square bracket left square bracket straight O right square bracket squared end fraction space... space left parenthesis straight i right parenthesis
left parenthesis equilibrium space constant space on space the space basis space of space conc. right parenthesis
and space straight K subscript straight p space equals space fraction numerator straight P subscript Co subscript 2 end subscript over denominator straight P subscript CH subscript 4 end subscript space straight x space straight P subscript straight O subscript 2 end subscript squared space end fraction space space space space.... space left parenthesis ii right parenthesis
left parenthesis Equilibrium space constant space according space to space partial space pressure right parenthesis
Thus space in space it space concentration space of space CO subscript 2 space left parenthesis straight g right parenthesis space and space straight H subscript 2 straight O space left parenthesis straight l right parenthesis space are space not space equilibrium
The space equilibrium space constant space left parenthesis straight K subscript straight p right parenthesis space equals space fraction numerator left square bracket CO subscript 2 right square bracket over denominator left square bracket CH subscript 4 right square bracket left square bracket straight O subscript 2 right square bracket space end fraction
    not correct expression.
    In addition of CH4 (g) or O2 (g) at equilibrium Kc = will be decreased according to expression (i) but Kc remains constant at constant  at constant temperature fro a reaction, so for maintaining the constant value of Kc, the concentration of CO2 will increase in same order. Hence, on the addition of CH4 or O2 equilibrium will cause to the right.
    This reaction is an example of an exothermic reaction.

    Question 406
    CBSEENCH11008443

    Which of the following pairs consitutes a buffer?

    • HNO2 and NaNO2

    • NaOH and NaCl

    • HNO3 and NH4NO3

    • HCl and KCl

    Solution

    A.

    HNO2 and NaNO2

    A pair constituent with an HNO2 and NaNO2 because HNO2 is weak acid and NaNO2 is a salt of the weak acid (HNO2) with a strong base (NaOH). Hence, it is an example of acidic buffer solution.

    Question 407
    CBSEENCH11008444

    The hydrogen ion concentration of a 10-8 M HCL aqueous solution at 298 K (Kw = 10-14) is:

    • 1.0 x 10-6

    • 1.0525 x 10-7 M

    • 9.525 x 10-8 M

    • 1.0 x 10-8 M

    Solution

    B.

    1.0525 x 10-7 M

    In aqueous solution of 10-8 M HCl, [H+] is based upon the concentration of H+ ion of 10-8 M HCl and concentration of H+ ion of water Kw of H2O = 10-14 = [H+][OH-] or [H+] = 10-7 M (due to neutral behaviour) os, in aqueous solution of 10-8 M HCl,
    [H+] = [H+] of HCl +[H+] of water
    = 10-8 + 10-7 = 11 x 10-8 M
    1.10 x 10-7 M

    Question 408
    CBSEENCH11008449

    Which of the following, not a correct statement? 

    • The electron -deficient molecules can act as Lewis acids

    • The canonical structures have no real existence

    • Every AB5 molecules does, in fact, have square pyramid structure

    • Multiple bonds are always shorter than corresponding single bonds

    Solution

    C.

    Every AB5 molecules does, in fact, have square pyramid structure

    Every AB5 molecule does not, in fact, have square pyramidal structure but AB5 molecules have trigonal bipyramidal structures due to sp3d hybridisation.

    Question 409
    CBSEENCH11008454

    HgCl2 and I2 both when dissolved in water containing I ions the pair of species formed is

    • HgI2 , I3-

    • Hgl2, I-

    • HgI43-, I3-

    • Hg2I2, I-

    Solution

    C.

    HgI43-, I3-

    In a solution containing HgCl2, I2 and I–, both HgCl2 and I2
    compete for I.
    Since formation constant of [HgI4]2– is 1.9 × 1030
    which is very large as compared with I3 (Kf= 700)
    therefore, I will preferentially combine with HgCl2
    HgCl2 + 2l- → Hgl2↓ + 2Cl-
    Hgl2 + 2l- → [Hgl4]2-

    Question 410
    CBSEENCH11008486

    When 750 mL of 0.5 M HCl is mixed with 250 mL of 2 M NaOH solution, the value of pH will be

    • pH = 7

    • pH > 7

    • pH < 7

    • pH = 0

    Solution

    B.

    pH > 7

    nHCl = MHCl x VHCl and nNaOH = MNaOH x VNaOH

    where n = number of moles

    M = molarity, V = volume

    ∴ nHCl  = 0.5 x 750 = 375 milimoles

    nNaOH = 2.0 x 250 = 500 milimoles

    ∵ nNaOH > nHCl

    The solution is basic and has pH > 7

    Question 411
    CBSEENCH11008487

    The most stable carbonium ion among the following is

    • C6H5 -CH2C+H2

    • CH3CH2+

    • C6H5 -C+-C6H5

    • C6H5C+H2

    Solution

    C.

    C6H5 -C+-C6H5

    Due to more possibility for delocalisation in 

    C6H5 - C+ -C6H5 (of π -electrons),C6H5 _C+ -C6H5 is the most stable ion.

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