Question

In electrolysis of Al₂O₃ by Hall-Heroult process :

(A) cryolite Na₃[AlF₆] lowers the melting point

(B) Al is obtained at cathode and probably CO₂ at anode

(C) both (A) and (B) are correct

(D) none of the above is correct

Answer 1

Correct Answer is: (C) both (A) and (B) are correct

Na₃[AlF₆] → 3NaF +AlF₃

so ionise to give ions. This increases the electrical conductivity and lowers the melting point of Al₂O₃ .

point of Al₂O₃ . At cathode :Al³⁺ (melt) + 3e^– →  Al.

At anode : C(s) + O^2– (melt)—→ CO (g) + 2e^– ; C(s) + 2O^2– (melt)—→ CO² (g) + 4e^–.