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Chemistry Paper 2 (Essay) ,May/June 2010  
Questions:   1 2 3 4 5 6 7 8   Main
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Question 7

(a) Name one product of destructive distillation of coal that is
        (i)              Solid;
        (ii)             Liquid;
        (iii)            Gas. [3 marks]

(b)    (i) What is the major component of synthetic gas?
(ii) Give one reason why synthetic gas is not a major source of air pollution. [2 marks]

(c)   (i) Write a balanced chemical equation for the complete combustion of carbon.
(ii)State two:
I. physical;
II. chemical properties of the product in 7 (c )(i) [ 5 marks]

(d) (i) Name two allotropes of carbon that are

1. crystalline;
II. amorphous.

(ii) State one use of each of the allotropes named in 7(d)(i). [ 8 marks]

(e) (i) By means of balanced chemical equations only, outline the process of manufacture of H2S04 by contact process.
(ii) State the function of H2S04 in each of the following reaction equations:
                1.              C2H5OH(l) cone H2S04 →C2H4(g);

                II.            Pb(NO3)2(aq) + H2S04(aq)    → PbS04(s) + 2HN03(aq)      [ 7 marks]




_____________________________________________________________________________________________________
OBSERVATION

The question was popular among candidates and the performance was good.

In (a), candidates correctly named one product of destructive distillation of coal that was solid, liquid and gas in (i)-Ciii) as coke, arnrnoniacalliquour/coal tar and coal gas respectively.

In part (b) only few candidates knew that methane was the maj or component of synthetic gas and that synthetic gas was not a major source of air pollution because it does not contain sulphur or sulphur compounds/sulphur was removed in the gasification process.

In part (c), most candidates were able to correctly write a balanced chemical equation for the complete combustion of carbon and stated two physical and two chemical properties of the product formed as follows:
(i) C(s) + 02(g) CO2(g)
(ii) I.  -   it is a gas at room temperature
          -   it is a colourless gas
          - it is odourless gas
          - it is denser than air
           -  it is soluble in water
             - it readily liquefies and solidifies/easily compressible

II.        - reacts with alkali to form trioxocarbonate(IV)
- reacts with (burning) Mg to form MgO
- reacts with red hot carbon to form CO
- it is weakly acidic in water
- it does not support combustion

In part (d), candidates named two crystalline and two amorphous carbon and one use of each of the named allotropes.
In part (e) (i), candidates were able to outline the process of manufacture of H2S04 by contract process. However some lost mark because of reversibility sign. The expected responses from candidates were:



In part (e)(ii), only few candidates correctly stated the function of H2S04 as dehydrating agent and precipitating/displacement agent in I and II respective.



 

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