Periodic Classification of Elements

  • Question 1
    CBSEENSC10010553

    What is a chemical equation? Illustrate with an example.

    Solution

    The mode of communicating facts in chemical language about a chemical reaction is called chemical equation. Thus, a chemical equation is an expression for given chemical change in terms of symbols or formula of the reactants and products. For example, the reaction of zinc with dilute sulphuric acid to produce zinc sulphate and hydrogen is given by the following chemical equation:
    Zn + H2SO→ ZnSO4 + H2

    In aobve reaction those are left-hand side is reactant and other part that is left hand side is product. 

    Question 2
    CBSEENSC10010554

    How will you know whether a chemical reaction has taken place?

    Solution

    When a chemical reaction occurs, one or more of the following changes take place :

    (i)    Change in state
    (ii)    Change in colour
    (iii)    Evolution of a gas    
    (iv)    Change in temperature.

    Question 3
    CBSEENSC10010555

    How would you justify that a chemical reaction has taken place in the following cases:
    (i)    Burning of magnesium ribbon in air.
    (ii)    Addition of lead nitrate solution to potassium iodide solution.
    (iii)    Addition of dilute hydrochloric acid to zinc granules.

    Solution

    (i) Burning of magnesium ribbon in air gives a powder (of MgO). So there is a change of state.

    Magnesium + Oxygen --> Magnesium oxide(MgO)

    (ii) Addition of colourless lead nitrate solution to potassium iodide solution gives yellow
    coloured precipitate (lead iodide). So there is a change of colour.

    (iii) Addition of dilute hydrochloric acid to zinc granules gives a gas (H2) with effervescence.

    Question 4
    CBSEENSC10010556

    How do you show that respiration is a chemical change?

    Solution
    During respiration, energy is released.Respiration is a form of oxidation.

    Glucose is oxidised to CO2 and H2O (along with release of energy) at the cells by the oxygen from air we breathe in.

          C6H12O6 + 6O2 = 6CO2 + 6H2O+energy

    Since glucose is converted into new products with different composition, respiration is a chemical change.

    Sponsor Area

    Mock Test Series

    Sponsor Area

    NCERT Book Store

    NCERT Sample Papers

    Entrance Exams Preparation