Question

Observe the following options and choose the incorrect one for Hall-Hèrault’s process for the extraction of aluminium.

• A. Cryolite $\left(N{a}_{3}Al{F}_6\right)$ is added to alumina $\left(A{l}_2{O}_3\right)$ to decrease the melting point.
• B. To increase the electrical conductivity, fluorspar $\left(Ca{F}_2\right)$ is added to the electrolyte.
• C. Almost 99.5% pure aluminium obtained at the anode in molten form.
• D. The anode used in this process is made up of graphite.

Answer 1

The correct option is C Almost 99.5% pure aluminium obtained at the anode in molten form.

In the Hall-Hèrault’s process, cryolite $\left(N{a}_{3}Al{F}_6\right)$ is added to alumina to decrease its melting point. Adding fluorspar $\left(Ca{F}_2\right)$ increases the ability of alumina-cryolite mixture to conduct electricity.
The steel case coated with carbon lining acts as cathode and graphite acts as an anode. When electricity is passed through the electrolytic cell, oxygen is formed at the anode while almost 99.5% pure aluminium is obtained at the cathode in molten form.