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Chemistry Paper 2 (Essay) ,May/June 2009  
Questions:   1 2 3 4 5 6 7 8   Main
General Comments

Question 3

  • (a)        (i)      Define polymerization.  
    (ii)     Mention two types of polymerization.  
    (iii)    Give one example of                                     

    1. naturally occurring polymer;
    2. synthetic polymer.                                                                             [6 marks]

    (b)        (i)      Describe how ethyne could be prepared in the laboratory.
    (ii)     Write an equation for the

    1. polymerization of ethyne.  
    2. complete reaction of ethyne with hydrogen bromide.

    (iii)    Name each of the products formed in 3(b)(ii)II.                                        [11 marks]

    (c)        (i)      Define each of the following terms:

    1. pollution;   
    2. pollutant.

    (ii)    Mention three types of pollution. 
    (iii)   Give two ways by which pollution can be prevented.
                                                                                                                     [8 marks]              

  • _____________________________________________________________________________________________________
  • The question was attempted by most candidates and the performance was good.
  • In part (a)(i), candidates correctly defined polymerization as a process whereby many small molecules (monomers) link together to form a giant molecule (polymer).  In (a)(ii), many of the candidates thought natural and synthetic polymer are the two types of polymerization hence they lost marks.  The expected answers from them were addition and condensation polymerization.
    In (a)(iii), some candidates could not correctly give one example of naturally occurring polymer and synthetic polymer.  The required answers were:

    1. starch/cellulose/proteins/natural rubber/latex
    2. polythene (polyethene)/PVC/polystyrene/nylon/perplex.

    In (b)(i), candidates were able to correctly describe the laboratory preparation of ethyne as follows:

    The action of water on calcium dicarbide evolved a gas which was passed through a solution of copper (II) tetraoxosulphate (VI) to remove impurities and ethyne is collected over water by upward delivery.

    In (b)(ii), candidates wrote equation for the polymerization of ethyne and complete reaction of ethyne with hydrogen bromide thus:

    1. 3C2H2(g)             C6H6(g)
    2. C2H2   +   2HBr            C2H4Br2

    In (b)(iii), the name of each of the products was given as benzene and l, 1 – dibromomethane respectively.

    In (c)(i), candidates correctly defined pollution and pollutant thus:

    1. Pollution is the presence of harmful substances in the environment in concentrations that can cause injury to life and property.
    1. Pollutants are harmful substances in the environment.

    They are also able to mention three types of pollution and two ways by which pollution could be prevented in (c)(ii) and (iii) respectively, as follows:

    1. -      air pollution;
    2. water pollution;
    3.   land/soil pollution.
    1. -       use of anti-pollutants in automobiles
    •    promulgation of laws with effective monitoring
    •   oil spillage prevention
    •   enlightenment programme
    •   tree planting
    •   proper sewage disposal.


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