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Question
For sodium hydroxide, explain its significance in the extraction of aluminium.
Solution 1
The ore from which aluminium is extracted must first be treated with sodium hydroxide solution so that pure aluminium oxide can be obtained.
Solution 2
Sodium hydroxide (NaOH) dissolves bauxite to form sodium meta-aluminate, removes soluble impurities and gives \[\ce{Al(OH)3↓}\] from which \[\ce{Al2O3}\] is obtained by heating.
\[\ce{Al2O3.2H2O + 2NaOH -> 2NaAlO2 + 3H2O}\]
\[\ce{NaAlO2 + 2H2O -> NaOH + Al(OH)3↓}\]
\[\ce{2Al(OH)3 ->[heat][1000^\circ C] Al2O3 + 3H2O}\]
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