(a)(i) Draw and label a diagram to illustrate the preparation and collection of dry chlorine gas in the laboratory. (ii) State two uses of chlorine. (b) Des...

(a)(i) Laboratory preparation and collection of dry chlorine gas

Chlorine is prepared by heating manganese(IV) oxide with concentrated hydrochloric acid:

\[MnO_2(s)+4HCl(aq)\rightarrow MnCl_2(aq)+Cl_2(g)+2H_2O(l)\]

The gas is passed through saturated sodium chloride solution to remove hydrogen chloride, then through concentrated sulphuric acid to dry it. It is collected by downward delivery, that is, by upward displacement of air, because chlorine is denser than air and dissolves in water.

(ii) Uses of chlorine

1. It is used to disinfect and sterilize drinking water.
2. It is used as a bleaching agent for paper pulp and textiles.

(b) Preparation of hydrogen from water gas

Water gas, a mixture of carbon(II) oxide and hydrogen, is mixed with steam and passed over heated iron(III) oxide or chromium(III) oxide catalyst at about \(450^\circ\mathrm{C}\). The carbon(II) oxide is converted to carbon(IV) oxide, producing more hydrogen:

\[CO(g)+H_2O(g)\rightarrow CO_2(g)+H_2(g)\]

The carbon(IV) oxide is removed by absorption in water under pressure or in aqueous sodium hydroxide, potassium hydroxide, or calcium hydroxide. The gas remaining is hydrogen.

(c)(i) The chief ore of aluminium is bauxite, \(Al_2O_3\cdot 2H_2O\).

(ii) The ore is purified to obtain alumina and to remove impurities, such as iron(III) oxide and silica, which would contaminate the aluminium and may poison the electrodes.

(iii) The electrodes used are carbon (graphite) electrodes.

(iv) Cryolite, \(Na_3AlF_6\), is added to lower the melting point of alumina, thereby reducing the energy required for electrolysis. It also increases the electrical conductivity of the electrolyte.

(d) Three products obtained directly from the destructive distillation of coal are:

1. coke;
2. coal tar;
3. coal gas.

Ammoniacal liquor is also obtained.