Question

During extraction of aluminum from bauxite,

• A. The concentration of ore is done by gravity separation method.
• B. Molten mixture of aluminum oxide, cryolite or 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)

Molten mixture of aluminum oxide, cryolite or fluorspar is electrolysed

Answer 2

Purified $Al_{2}O_{3}$ is mixed with $Na_{3}AlF_{6}$ and $CaF_{2}$ to improve conductivity of $Al_{2}O_{3}$ and to lower the melting point.

$Al_{2}O_{3}\overset{\quad electrolysis\quad}{\rightarrow}2Al^{3 +} + 3O^{2 -}$

At cathode : $Al^{3 +} + 3e^{-} \rightarrow Al$

At anode : $C + O^{2 -} \rightarrow CO + 2e^{-}$

$C + 2O^{2 -} \rightarrow CO_{2} + 4e^{-}$