Question

Give the ionization reactions of electrolyte used in Hall’* process. write the reaction at the cathode and the anode. Why the anode has to be replaced in this process?

Answer 1

*The ionization reactions of electrolyte in Hall' process.**

1. Cryolite: Na3AlF6 ⇌ 3Na+ + Al3+ + 6F-

2. Fluorspar: CaF2 ⇌ Ca2+ + 2F-

3. Alumina: Al2O3 ⇌2Al3+ + 3O2-

The reaction at the cathode and anode are:

Cathode:

4Al3+ + 12e-→ 4Al

Anode:

6O2- -12e- → 6[O]

3O + 3O → 3O2

The anode has to be replaced from time to time as it gets oxidized by the oxygen evolved at the anode.