Question

In the Hall's process for extraction of aluminium, Sate the location of cathode and anode and explain what occurs at each electrode.

Answer 1

Cathode is the inner lining of gas-carbon of the electrolytic cell and anode is the thick carbon rods dipping into the fused electrolytes.
At cathode: Aluminium ions get reduced as:
Al³⁺ + 3e^- → Al
At anode: oxygen gas is liberated as:
O^2- - 2e^- → [O]
[O] + [O] → O₂
The oxygen formed at anode oxidizes the carbon of the anode to carbon dioxide.

C + O₂ → CO₂
As a result the anode gets oxidized and it has to be replaced periodically.