Question

7. (Questions 5 and 6 in the original paper are not for Nigeria and are omitted.)
(a)(i) Explain briefly the term chemical industry. (ii) State three factors that should be considered in siting a chemical industry.
(b)(i) Describe briefly how tin is extracted from its ore. (ii) Give two uses of tin.
(c)(i) Name the constituents of cement. (ii) How does mortar set?
(d)(i) Explain briefly the term pollution. (ii) Give two examples of air pollutants.
(e) Consider the following reversible reaction which occurred at the temperature of 298k: N2+3H2(g) ⇌ 2NH3(g); ΔH=−92.37 kJ. List two factors that would increase the yield of NH3(g).

Accepted Answer

(a)(i) A chemical industry simply refers to an industry that utilizes chemical processes for converting raw materials into useful products.
(ii) Factors to be considered in siting a chemical industry: Nearness to the source of raw material; Government policy; Nearness of market.

(b)(i) The tin ore (cassiterite) is first concentrated and then roasted in air to remove impurities. The roasted ore is heated in a furnace to a very high temperature after being mixed with coke. Limestone is added to remove impurities. The tin is collected in molten form.
(ii) Tin is used in making alloys; It is used for coating other metals.

(c)(i) The major components of cement are: Calcium carbonate, silicon oxide and aluminum oxide.
(ii) Mortar which is a mixture of sand, cement and water hardens by the absorption of CO2 from the atmosphere. This leads to the production of CaCO3.

(d)(i) Pollution is the process of introducing harmful and/or unwanted substances into environment.
(ii) Examples of air pollutants: Carbon monoxide; Dust.

(e) The two factors that will increase the yield of ammonia are: Decrease in temperature; Increase in pressure.

WAEC Chemistry 2013 Theory — Question 5

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