Question -
Answer -
In the electrometallurgy ofaluminium, a fused mixture of purified alumina (Al2O3), cryolite (Na3AlF6) and fluorspar (CaF2) is electrolysed. In this electrolysis,graphite is used as the anode and graphite-lined iron is used as the cathode.During the electrolysis, Al is liberated at the cathode, while CO and CO2 are liberated at the anode, according tothe following equation.
If a metal is used instead ofgraphite as the anode, then O2 will be liberated. This will not onlyoxidise the metal of the electrode, but also convert some of the Al liberatedat the cathode back into Al2O3. Hence, graphite is used for preventing theformation of O2 atthe anode. Moreover, graphite is cheaper than other metals.