In the extraction of aluminium from bauxite, the first step is the dressing of the ore by Baeyer's process. Give balanced equations for the conversion of impure bauxite to pure alumina using a concentrated solution of NaOH.

Conversion of impure bauxite to sodium aluminate:

$\underset{\text{Amphoteric oxide}}{\underset{\text{[Impure bauxite]}}{\text{Al}$2\text{O}3.2\text{H}2\text{O }}} + \underset{\text{Base}}{\underset{\text{[conc. soln]}}{2\text{NaOH }}} \xrightarrow{150 - 200 \degree\text{C}} \underset{\text{Salt}}{\underset{\text{[sodium aluminate]}}{2\text{NaAlO}2}} + \underset{\text{Water}}{ \text{3H}_2\text{O}}

Conversion of sodium aluminate to aluminium hydroxide:

$\underset{\text{[sodium aluminate]}}{\text{NaAlO}$2} + 2\text{H}2\text{O} \xrightarrow{50 - 60 \degree\text{C}} \underset{\text{[sodium hydroxide]}}{\text{NaOH}} + \underset{\text{[aluminium hydroxide]}}{\text{Al(OH)}_3}

Conversion of Al(OH)₃ - to pure alumina - heat on Al(OH)₃:

$\underset{\text{[aluminium hydroxide]}}{\text{2Al(OH)}$3} \xrightarrow{1100\degree\text{C}} \underset{\text{[pure alumina]}}{\text{Al}2\text{O}3} + \text{3H}2\text{O}