The s-Block Elements

  • Question 141
    CBSEENCH11007119

    Can we prepare potassium bicarbonate by Solvay process?

    Solution
    Potassium bircarbonate which is to be formed in the process is highly soluble in water and cannot be precipitated.
    Question 142
    CBSEENCH11007120

    What is the action of heat on Na2CO3.10H2O?

    Solution

    On heating below 373K, it loses 9 molecules of water of crystallisation to form monohydrate (Na2CO3.H2O). On heating above 373K, the monohydrate changes to an anhydrous white powder called soda ash but does not decompose further.
           
    Na subscript 2 CO subscript 3. space 10 straight H subscript 2 straight O space rightwards arrow with Below space 373 space straight K on top space Na subscript 2 CO subscript 3. space straight H subscript 2 straight O space plus space 9 straight H subscript 2 straight O
space space space Na subscript 2 CO subscript 3. space straight H subscript 2 straight O space rightwards arrow with Above space 373 space straight K on top space Na subscript 2 CO subscript 3 space plus space straight H subscript 2 straight O

    Question 143
    CBSEENCH11007121

    State as to why a solution of Na2COis alkaline.

    Solution
    Na2CO3 is a salt of strong base (NaOH) and weak acid (H2CO3). When Na2CO3 is dissolved in water, it undergoes hydrolysis to produce strong base (NaOH) and weak acid (H2CO3). Hence its aqueous solution is alkaline in nature.
    Na subscript 2 CO subscript 3 left parenthesis straight s right parenthesis space plus space straight H subscript 2 straight O left parenthesis straight l right parenthesis space rightwards arrow space space space stack 2 NaOH left parenthesis aq right parenthesis with Strong space base below space plus space stack straight H subscript 2 CO subscript 3 left parenthesis aq right parenthesis with Weak space acid below
    Question 144
    CBSEENCH11007122

    What happens when:
    (i) sodium carbonate reacts with the milk of lime.
    (ii) sodium carbonate is added to water.
    (iii) sodium carbonate reacts with a dilute mineral acid?

    Solution
    (i) It reacts with hot milk of lime to form sodium hydroxide
    Na subscript 2 CO subscript 3 space plus space Ca left parenthesis OH right parenthesis subscript 2 space space rightwards arrow space space space CaCO subscript 3 downwards arrow space plus space NaOH.
    (ii) It undergoes hydrolysis to form an alkaline solution.
      Na subscript 2 CO subscript 3 space plus space 2 straight H subscript 2 straight O space rightwards arrow space space space straight H subscript 2 CO subscript 3 space plus space 2 NaOH.
    (iii) It reacts with dilute mineral acid evolving CO2 gas. 
    Na subscript 2 CO subscript 3 space plus space 2 HCl space rightwards arrow space space space 2 NaCl space plus space straight H subscript 2 straight O space plus space CO subscript 2.

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