a)(i) Give two uses of ammonia. (ii) Name the process by which ammoniacal liquor can be obtained from coal and list two other products of the reaction (iii)...

(a)(i) Two uses of ammonia are:

• Manufacture of fertilizers such as ammonium sulphate and ammonium nitrate.
• Manufacture of trioxonitrate(V) acid, i.e. nitric acid.

(a)(ii) Ammoniacal liquor is obtained by the destructive distillation of coal.

Two other products are:

• Coke
• Coal tar

Coal gas is also produced.

(a)(iii) The reaction is a neutralisation (acid-base) reaction.

\(2NH_3 + H_2SO_4 \rightarrow (NH_4)_2SO_4\)

(a)(iv) Energy profile diagram for the reaction:

The reaction is exothermic because the products are at a lower energy level than the reactants. Pt/Rh lowers the activation energy but does not change the value of \(\Delta H\).

(b)(i) Procedure for preparing pure sodium chloride from rock salt:

• Crush the rock salt and dissolve it in water.
• Filter the mixture to remove insoluble impurities such as sand.
• Evaporate the filtrate until it is nearly saturated.
• Allow the solution to cool so that sodium chloride crystals form.
• Filter, wash the crystals with a little cold distilled water and dry them.

(b)(ii) Two methods of preparing chlorine from rock salt are:

• Electrolysis of concentrated sodium chloride solution (brine):
  \(2NaCl(aq) + 2H_2O(l) \xrightarrow{\text{electrolysis}} 2NaOH(aq) + H_2(g) + Cl_2(g)\)
• Oxidation of sodium chloride with manganese(IV) oxide and concentrated tetraoxosulphate(VI) acid:
  \(2NaCl + MnO_2 + 2H_2SO_4 \rightarrow Cl_2 + MnSO_4 + Na_2SO_4 + 2H_2O\)

(c)(i) The air pollutant is hydrogen sulphide, \(H_2S\).

(c)(ii) The black substance is lead(II) sulphide, \(PbS\).

(c)(iii) The white salt is lead(II) tetraoxosulphate(VI), \(PbSO_4\).

(c)(iv) Hydrogen peroxide, \(H_2O_2\), acts as an oxidising agent. It oxidises black lead(II) sulphide to white lead(II) sulphate:

\(PbS + 4H_2O_2 \rightarrow PbSO_4 + 4H_2O\)