Question

Observe the following diagram and write answers.

1. Name the method.
2. Write anode reaction and cathode reaction.
3. Why fluorspar and cryolite are added in the mixture?

Answer 1

1. This method is electrolytic reduction of alumina.
2. Anode reaction:
   \[\ce{2O^{2-} -> O2 + 4e^-}\] (Oxidation)
   Cathode reaction:
   \[\ce{Al^{3+} + 3e^- -> Al_{(l)}}\] (Reduction)
3. Alumina has a very high melting point (>2000 °C). The purpose of mixing ‘cryolite’ and ‘fluorspar’ with ‘alumina’ in the electrolytic reduction of alumina is to carry out the process at a much lower temperature. Addition of cryolite and fluorspar reduces the melting point of alumina to about 1000 °C.