Question

What is the net reaction in Hall-Heroult process?

(a) 2Al2O3 + 3C → 4Al + 3CO2

(b) 4Al2O3 + 3C → 4Al + 6CO2

(c) F2 + Al2O3 → Al + F2O3

(d) Na3AlF6 → AlF3 + 3NaF

I had been asked this question in a job interview.

My question is taken from Electrochemical Principles of Metallurgy topic in chapter General Principles and Processes of Isolation of Elements of Chemistry – Class 12

Answer 1

Correct choice is (a) 2Al2O3 + 3C → 4Al + 3CO2

To elaborate: The reaction involved in Hall-Heroult process are:-

Na3AlF6 → AlF3 + 3NaF

AlF3 → Al^+3 + 3F^–

Cathode: Al^+3 + 3e^– → Al

Anode: 6F^– → 3F2 + 6e^–

F2 + Al2O3 → AlF3 + O2

C + O^2- → CO or CO2 + 2e^–

The overall reaction may be written as 2Al2O3 + 3C → 4Al + 3CO2.