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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 1

(a) (i)     Give the name and nature of the radiations that are emitted during radioactivity.
(ii) State two differences between chemical reaction and nuclear reaction.
(iii) Balance the following nuclear reactions and identify X and Y
       I.               21284PO → 20882Pb + X

       II.             13755Cs → 13756Ba + Y                                                 [12 marks]


(b) The electron configuration of an element X is:
             IS22s22p63s23p5
              (i)           Deduce the atomic number of X.
              (ii)          To what group does X belong?
              (iii)         Give two properties of the group to which the element X belong.
              (iv)         Identify element X by name.
              (v)          Write a balanced equation to represent the reaction between the element X and hot                             concentrated NaOH
(c)       (i) Explain why:
                      1.             graphite is used as a lubricant;
                      II.             diamond is used as an industrial cutting tool.[7 marks]
            (ii)   Write an equation to represent the reaction between aqueous BCL and NH3 solution.
            (iii) Name the type of reaction represented by the equation.                                 [ 6 marks]



_____________________________________________________________________________________________________
OBSERVATION

The question was attempted by majority of the candidates and the performance was good.

In part (a)(i), candidates correctly gave name and corresponding nature of the radiations emitted during radioactivity as follows:

- alpha particle, (doubly charged) helium nucleus/high ionizing/low penetrating power/deflected towards negative plate
- beta particle, (fast moving) electron/moderate ionizing/moderate penetrating power/deflected towards positive plate
- gamma radiation, (high energy) electromagnetic radiation/low ionizing/high penetrating power/no effect on magnetic field.

Some candidates however lost marks because of spelling mistakes and use of symbols to denote the particles (i.e alfa for alpha or a instead of alpha).

In part (a)(ii), only very few candidates were able to give corresponding differences between chemical reaction and nuclear reaction as follows:

Chemical reaction

 

Nuclear reaction

- atoms are rearranged by the

-

elements are converted to other

breaking and forming of chemical

 

elements/new elements may be

bond/no new atom is

 

formed/atomic number or mass

formed/atomic number or mass

 

number of each element may change.

number of each element does not    
change    
- only (valence) electrons are
involved.
  - protons, neutrons, electrons and other
elementary parties may be involved.
- reactions are accompanied by
absorption/release of (relatively)
small amount of energy.
  - reactions are accompanied by release
of (relatively) large amount of energy.

- rate of reaction is influenced by
temperature, pressure,
concentration and catalyst.

 

- rate of reaction normally are not
affected by pressure, temperature and
catalyst.



In(a)(iii), most candidates correctly balanced the nuclear reactions and identify X and Y thus:

     (iii)               21284PO → 20882Pb +42 X                    X is α- particle/helium nucleus I42He

                  13755Cs → 13756Ba + 0-1Y                           Y is β - particle/electron    0-1e

In part (b) (i) - (v), majority of the candidates correctly answered as follows:
(i)            atomic number - 17
(ii)           group 7
(iii)           - formation of diatomic molecules
                 - formation of monovalent ions/same valence electrons
                 - they are coloured substances
                 - they are oxidizing agents
                 - most electronegative in its period/smallest atomic size in its period
                 - they are non metals
(iv)         chlorine (formula was not accepted)
(v)          3Cl2 + 6NaOH   →   5NaCl + NaCl03 + 3H20
However, some of the candidates lost marks because they could not give a correct balanced equation for the reaction of element X and hot concentrated NaOH.

In part (c )(i), most candidates lost marks because they did not know that graphite was used as a lubricant because of its planar layers which slides over each other and that diamond has three dimensional network which makes it so hard hence, used as a cutting tool in I and II respectively.

In part (c)(ii), candidates correctly wrote the reaction equation thus:

 

Also the gave the name of the reaction as combination/neutralization in (iii).

 

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