Question

In the extraction of aluminium by Hall-Heroult process, purified $A{l}_2{O}_3$ is mixed with $Ca{F}_2$ to:

• A. Lower the melting point of $A{l}_2{O}_3$ mixture
• B. Increase the conductivity of molten mixture
• C. Reduce $A{l}^{3+}$ into $Al\left(s\right)$
• D. Acts as catalyst

Answer 1

Answer: (A), (B)

Increase the conductivity of molten mixture

In the extraction of aluminium by Hall Heroult process, $A{l}_2{O}_3$ is mixed with $Ca{F}_2$ or $N{a}_{3}Al{F}_6$ as it lowers the melting point of the mixture and increases the conductivity of the electrolyte. $A{l}^{3+}$ is reduced at the cathode to form $Al$
Therefore, the correct options are A and B.