Question

The following questions are relevant to the extraction of aluminum.

State the reason for the addition of caustic alkali to bauxite ore during the purification of bauxite.

Answer 1

1. Bauxite or Aluminum oxide($\mathit{A}{\mathit{l}}_{\mathbf{2}}{\mathit{O}}_{\mathbf{3}}$) is the ore of Aluminum.
2. For removing the impurity Aluminum oxide present in Bauxite caustic alkali that is Sodium hydroxide is added.
3. By the reaction Sodium aluminate and hydrogen gas are produced thereby dissolving the aluminum oxide impurity of the ore.
4. The reaction is,

$\underset{Aluminumoxide}{A{l}_2{O}_3\left(s\right)}+\underset{Sodiumhydroxide}{NaOH\left(aq\right)}\to \underset{Sodiumaluminate}{2NaAl{O}_2\left(s\right)}+\underset{Hydrogen}{H_2\left(g\right)}$

So caustic alkali is added to remove or dissolve the Aluminum oxide impurity.