Chemistry [4 MARCK QUESTION]

(i) A shining coppery colour (red) is formed on the cathode due to the deposition of copper metal.
(ii) The anode slowly dissolves, but the colour of copper sulphate does not change. Shining reddish colour of copper appears at anode because of the removal of copper atoms.
(iii) At the anode, reddish vapours of bromine escape in air from molten lead bromide.
(iv) When copper sulphate solution is electrolysed using copper electrodes, fresh reddish copper metal is deposited at cathode and fresh surface of copper is exposed at anode. The colour of copper sulphate solution does not change.

(i) Sodium argentocyanide is a complex salt.
(ii) Sodium argentocyanide is preferred to silver nitrate as it does not hydrolyse in aqueous solution.
(iii) The metal to be electroplated should be absolutely free from oxides of metals, grease, etc., and low current density should be used.
(iv) Ag⁺ + e^- → Ag [at cathode]
Ag - e^- → Ag⁺ [at anode]

(a) On the passage of electric current through molten sodium chloride, sodium ions migrate to the cathode and chloride ions migrate to the anode.
At the cathode, sodium ions gain electrons and at the anode, chloride ions lose electrons to form sodium and chlorine atoms.
Na⁺ + e^- → Na [At cathode]
Cl^- - e^- → Cl [At anode]
(b) (i) Aluminium and sodium.
(ii) Alumina (Al₂O₃) for the manufacture of aluminium.
Sodium chloride (NaCl) for the manufacture of sodium.
(iii) Al³⁺ + 3e^- → Al (At cathode)
Na⁺ +e^- → Na (At cathode)