Aluminium is extracted from it's chief ore, bauxite. The ore is first purified and then the metal is extracted from it by electrolytic reduction.
(a) Write three balanced equations for the purification of bauxite.
(b) Name a chemical used for dissolving aluminium oxide. In which state is the chemical used?
(c) Write an equation for the reaction which takes place at the anode during the extraction of aluminium by the electrolytic process.
(a) The three balanced equations for the purification of bauxite are:
Al2O3.2H2O + 2NaOH ⟶ 2NaAlO2 + 3H2O
NaAlO2 + 2H2O ⟶ NaOH + Al(OH)3↓
2Al(OH)3 Al2O3 + 3H2O
(b) The chemical used for dissolving aluminium oxide is cryolite. It is used in molten state.
(c) At anode:
6O2- - 12e- ⟶ 6[O]
3[O] + 3[O] ⟶ 3O2
Anode is oxidised to carbon monoxide which further forms carbon dioxide
2C + O2 ⟶ 2CO
2CO + O2 ⟶ 2CO2