.(a)(i) Name two gases that can be used to perform the fountain experiment. (ii) What is the aim of he fountain experiment? (iii) Describe briefly the fount...

Answer Details

(a)(i) Two gases for the fountain experiment

Ammonia (\(NH_3\)) and hydrogen chloride (\(HCl\)); both are extremely soluble in water.

(a)(ii) Aim of the fountain experiment

To demonstrate the very high solubility of the gas in water.

(a)(iii) Description of the fountain experiment

A dry round-bottomed flask is filled with the dry gas (e.g. ammonia) and fitted with a stopper carrying a jet tube that dips into a beaker of water (containing an indicator such as litmus) and a small dropper of water. A little water is squeezed from the dropper into the flask. The gas dissolves rapidly and almost completely, creating a partial vacuum (reduced pressure) inside the flask. The greater atmospheric pressure on the water in the beaker then forces water up the jet tube, and it spurts into the flask as a fountain. The indicator changes colour (turning blue for ammonia), showing the gas is alkaline.

(b)(i) Two chemical industries

Petrochemical (oil-refining) industry and cement industry. (Also acceptable: fertilizer, brewery, soap and detergent, pharmaceutical industries.)

(b)(ii) Three effects of a chemical industry on its community

• Provision of employment and improved standard of living (positive).
• Provision of social infrastructure such as roads, water and electricity (positive).
• Air and water pollution and health hazards from the disposal of wastes and emission of gases (negative).

(c)(i) Three products of the destructive distillation of coal

Coke, coal gas, coal tar (and ammoniacal liquor).

(c)(ii) One use each of two products

• Coke: used as a fuel and as a reducing agent in the extraction of metals.
• Coal gas: used as a gaseous fuel for heating and lighting. (Coal tar: source of organic chemicals and for surfacing roads.)

(d)(i) Two substances responsible for hardness in water

Calcium and magnesium hydrogencarbonates and sulphates (\(Ca^{2+}\) and \(Mg^{2+}\) salts).

(d)(ii) Two methods of removing hardness

Boiling (for temporary hardness) and addition of washing soda, \(Na_2CO_3\) (also ion exchange or distillation).

(d)(iii) Two advantages of hard water

• It supplies calcium salts needed for the formation of strong bones and teeth.
• It has a pleasant taste and helps prevent lead poisoning by coating lead pipes with an insoluble layer.