Question

Write chemical equation for the event.

Electrolysis of alumina is done.

Answer 1

The electrolysis of alumina is carried out in a steel tank lined inside with graphite. The graphite lining serves as cathode. Anode is also made up of graphite rods hanging in the molten mass. The electrolyte consists of alumina dissolved in fused Cryolite(Na₃AlF₆) and Fluorspar(CaF₂). Cryolite lowers the melting point of alumina and fluorspar increases the fluidity of the mass so that the liberated aluminum metal may sink at the bottom of the cell. When electric current is passed through this mixture, the aluminum is collected at the cathode in molten state and sinks at the bottom.

Ionization of Alumina:2Al₂O₃ → 6O^-2 + 4Al⁺³
Reaction at  Cathode: 4Al⁺³ + 12e^- → 4Al
Reaction at Anode: 6O^-2 → 3O₂ + 12e^-, C + O₂ → CO₂

Answer 2

When electrolysis of alumina is done, aluminium is formed at the cathode and oxygen gas liberated at the anode.

Cathode:

\[\ce{Al^{3+} + 3e^- -> Al_{(l)}}\] (Reduction)

Anode:

\[\ce{2O^2- -> O_{2(g)} + 4e^-}\] (Oxidation)