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

Question

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

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

Answer 1

The graphite[carbon] anodes are continously replaced during the electrolysis because : 

(a) The oxygen evolved at the anode escapes as a gas or reacts with the carbon anode. 

(b) The carbon anode is thus oxidised to carbon monoxide which either bums giving carbon dioxide or escapes out through an outlet. 

2C + O₂ → 2CO [2CO + O₂ → 2CO₂ ] 

(c) The carbon anode is hence consumed and renewed periodically after a certain period of usage,