In the extraction of aluminium from bauxite, the first step is the dressing of the ore by Baeyer's process. Give balanced equations for the conversion of impure bauxite to pure alumina using a concentrated solution of NaOH.

In the electrolytic reduction of pure alumina to pure aluminium by Hall Herault's process, give the electrolytic reactions involved in the same, resulting in formation of aluminium at the cathode.

Give reasons for the following pertaining to Hall Herault's process.

(i) The fusion temperature of the electrolyte has to be lowered before conducting the electrolytic reduction.

(ii) The constituents of the electrolyte in addition to one part of fused alumina contains three parts of cryolite and one part of fluorspar.

(iii) A layer of powdered coke sprinkled over the electrolytic mixture, protects the carbon electrodes.

(iv) It is preferred to use a number of graphite electrodes as anode, instead of a single graphite electrode.

Define (a) alloy (b) amalgam