Question

4(a) [FOR CANDIDATES IN NIGERIA AND THE GAMBIA] The following reaction scheme is an illustration of the contact process. Study the scheme and answer the questions that follow.
(i) Name X and Y.
(ii) Write balanced chemical equations for each of the processes I, II, III and IV.
(iii) Name the catalyst used in process II.
(iv) Using Le Chatelier's principle, explain briefly why increasing the temperature would not favour the reaction in II.
(v) State two uses of SO2. [12 marks]

Accepted Answer

(i) X is oxygen while Y is sulphur.
(ii) I. S(s)+O2(g)→SO2(g)
  II. 2SO2(g)+O2(g)⇌2SO3(g)
  III. SO3(g)+H2SO4(aq)→H2S2O7(l) (oleum)
  IV. H2S2O7(l)+H2O(l)→2H2SO4(aq)
(iii) The catalyst used in process II is vanadium(V) oxide, V2O5.
(iv) The forward reaction (II) is exothermic, so by Le Chatelier's principle, increasing the temperature would only favour the backward (endothermic) reaction, reducing the yield of SO3.
(v) SO2 is used in the manufacture of H2SO4, and for bleaching wood pulp/wool/silk (also used for destroying bacteria and fungi/as a preservative).

WAEC Chemistry 2019 Theory — Question 19

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