Chemistry Paper 1 (Practical) ,May/June 2008

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Chemistry Paper 1 (Practical) ,May/June 2008

Questions:				1	2	3	4	5	6		Main

General Comments
Weakness/Remedies
Strength

Question 3
(a) In the laboratory preparation of crystals of CuSO`4`, a green powder Q was added to dilute H`2`SO`4` and stirred. Effervescence occurred and a gas R was given off which turned lime water milky. Excess Q was removed from the mixture. The solution of CuSO`4` was concentrated to half its original volume and allowed to stand. (i) What is substance Q? (ii) Name gas R. (iii) Why was excess Q used? (iv) How would you know that the reaction is complete? (v) What method was used to remove excess Q? (vi) Why was the solution of CuSO`4` not heated to dryness? [6 marks] (b) Name the reagent(s) used for testing each of the following substances in the laboratory: (i) Water; (ii) Primary alkanol. [2 marks]
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OBSERVATION
This question was attempted by few candidates and the performance was poor. Most candidates could not attempt 3(a) because they lacked the required laboratory experience. However, the expected responses to the questions were as follows: (a) (i) Q is copper(II) trioxocarbonate (IV)/ CuCO3 (ii) Carbon (IV) oxide (formula not acceptable) (iii) Excess Q was used to ensure that all the acid reacted (iv) When there is no more effervescence (v) Filtration (vi) To form crystals/ to concentrate the filtrate in order to form crystals on cooling or Heating to dryness the crystals of CuSO4 would not be obtained/ anhydrous CuSO4 will be obtained. In (b), only few candidates correctly named the reagent(s) used for testing water and primary alkanol in the laboratory as follows: White anhydrous copper (II) tetraoxosulphate (VI)/cobalt (II) chloride paper and alkaline iodine solution/acidified potassium tetraoxomanganate (VII)/acidified potassium heptaoxodichromate (VI) respectively.

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