Question

During extraction of aluminium from bauxite,

• A. the concentration of ore is done by gravity separation method
• B. molten mixture of aluminium oxide, cryolite and fluorspar is electrolysed
• C. impure aluminium is refined by liquation
• D. molten aluminium is obtained at cathode while fluorine is liberated at anode.

Answer 1

Answer: (B)

Purified $A{l}_2{O}_3$ is mixed with $N{a}_{3}Al{F}_6$ and $Ca{F}_2$ to improve conductivity of $A{l}_2{O}_3$ and to lower the melting point of the mixture.
$A{l}_2{O}_3\stackrel{\text{Electrolysis}}{\to }2A{l}^{3+}+3O^{2-}$
At cathode : $A{l}^{3+}+3e^{-}\to Al$
At anode : $C+O^{2-}\to CO+2e^{-}$
$C+2O^{2-}\to C{O}_2+4e^{-}$