(a) (i) - action of an acid upon an active metal / metals higher than hydrogen in the reactivity series
- preparation by double decomposition (reaction between two soluble compounds to produce an insoluble compound)
- by neutralization (reaction between acids & bases)
- action of an acid on trioxocarbonate (IV) of a metal
- direct combination of elements
- action of dilute acid on an insoluble base

Examples:
(ii) - Addition of granulated zinc to a dilute solution of tetraoxosulphate (VI) acid.

Zn(s) + H\(_2\)SO\(_{4(aq)}\) → ZnSO\(_{4(aq)}\) + H\(_{2(g)}\)
- Pb(NO\(_3\))\(_{2(aq)}\) + H\(_2\)SO\(_{4(aq)}\) → PbSO\(_{4(s)}\) + 2HNO\(_{3(aq)}\)

OR

Pb(NO\(_3\))\(_{2(aq)}\) + Na\(_{2}\)SO\(_{4(aq)}\) → PbSO\(_{4(s)}\) + 2NaNO\(_{3(aq)}\)
2NaOH\(_{(aq)}\) + H\(_{2}\)SO\(_{4(aq)}\) → Na\(_2\)SO\(_{4(aq)}\) + 2H\(_2\)O\(_{(l)}\)
ZnCO\(_{3(s)}\) + H\(_2\)SO\(_{4(aq)}\) → ZnSO\(_{4(aq)}\) + H\(_2\)O\(_{(l)}\) + CO\(_{2(g)}\)
- CaCO\(_{3(s)}\) + 2HCl\(_{(aq)}\) → CaCl\(_{2(aq)}\) + H2O\(_{(l)}\) + CO\(_{2(g)}\)
- 2Fe + 3Cl\(_2\) → 2FeCl\(_3\)
Fe + S → FeS
- 2HNO\(_3\) + CuO → Cu(NO\(_3\))\(_2\) + H\(_2\)O

(iii) Uses of Na\(_2\)CO\(_3\)
- used as a water softner
- manufacture of glass/paper/rayon/soaps/detergents/NaOH/Borax
- food processing aid
- pH modifier
- swimming pool chemical
- electrolyte
- analytical reagent / standardization of acids

(b) Use pure copper as the cathode and impure copper as anode and then use a named soluble copper salt e.g. CuSO\(_4\) solution as the electrolyte impure copper dissolves /CuCu\(^{2+}\) + 2e\(^-\) and will be deposited at cathode / Cu\(^{2+}\) + 2e\(^-\) Cu Wash the cathode to obtain pure copper.

(c) (i) Mass of NaCl deposited = 39.0 – 36.3 g = 2.7 g
% NaCl deposited = 2.7 x \(\frac{100}{39.0}\) = 6.92 % or 7.0%

Mass of AgNO\(_3\) deposited = 952.0 – 297.0 = 655 g
% AgNO\(_3\) = \(\frac{655}{952}\) x 100 = 68.8 % Or 69%

(ii) AgNO\(_3\) (Silver trioxonitrate (V)) will be more efficiently crystallized because it has a higher percentage deposited.