Question

Explain the method of obtaining pure aluminium from alumina by electrolysis . In this process , the carbon rods are replaced from time to time. Why ?

Answer 1

Pure $A{l}_2{O}_3$ mixed with cryolite undergo electrolysis.

At cathode: $A{l}^{2+}+3e^{-}\to Al$

At anode : $2O_2\to O_2+4e^{-}$

Carbon at anode reacts with $O_2$ and form $C{O}_2$. Thus anode gets used up. So anode is replaced frequently.