WAEC Chemistry 2020 Theory — Question 5

Model answer

(a)(i) Gases that can be used to perform the fountain experiment: Hydrogen chloride gas; Ammonia; Sulphur (IV) Oxide. (ii) It is to demonstrate the solubility of these gases. (iii) Water is introduced through an inlet into a container filled with ammonia gas. Ammonia dissolves into the water and the pressure in the container drops. As a result, more water is forced into the container from another inlet creating a fountain effect. (b)(i) Chemical industries: Pharmaceutical industry; Petroleum industry; Plastic industry; Petrochemical industry. (ii) Effects of a chemical industry on the community in which it is sited: Employment opportunity; Development of the community; Improvement of standard of living. (c)(i) Products of the destructive distillation of coal: Coke; Coal tar; Coal gas; Ammoniacal liquor. (ii) Uses of products: Coke is used in the extraction of iron. Coal tar is used to manufacture paints, perfumes, dyes and explosives. Coal gas is used as a fuel in industries. Ammoniacal liquor is used as a source of nitrogen (for fertilizer production). (d)(i) Substances responsible for hardness in water: Calcium hydrogen trioxocarbonate; Magnesium hydrogen trioxocarbonate; Calcium tetraoxosulphate (VI); Magnesium tetraoxosulphate (VI). (ii) Methods for removal of hardness: Distillation; Use of ion exchange resin; Use of washing soda. (iii) Advantages of hard water: Hard water tastes better because of the dissolved minerals in it; It does not dissolve lead pipe; Animals such as snails employ hard water in the formation of their shells.