Question

The following questions relate to the extraction of aluminium by electrolysis.
Explain why it is necessary to renew the anode periodically.

Answer 1

Oxygen gas is liberated at anode as :
\[\ce{O2- - 2e- -> [O] }\]
\[\ce{[O] + [O] -> O2}\]
The oxygen formed at anode oxidizes the carbon of the anode to carbon dioxide.
\[\ce{C + O2 -> CO2}\]
As a result the anode gets oxidized and it has to be replaced periodically.