CBSE Class 10 Answered

           Electrolysis of pure Al₂O₃ is impractical because it melts at very high temperature (2045^oC) and electrolysis of aqueous Al³⁺³⁺ ion. Thus use of cryolite as a solvent for Al₂O₃ is the key to the success of Hall – Heroult process. solution is not feasible because water is reduced in preference to Al

             The electrode reactions are still not fully understood, but they probably involve complex anions of the type AlF_xO_y^+3-x-2y formed by the reaction of Al₂O₃ with Na₃AlF₆. The complex anions are reduced at the cathode to molten Al metal and are oxidized at anode to O₂ from O₂^2- gas which reacts with graphite anodes to give CO₂ gas. As a result the anodes are chewed up rapidly and must be replaced frequently