Chemistry
State the relevant reason for the following:
(a) Concentrated alkali is used for the concentration of bauxite ore.
(b) Fused alumina is reduced to aluminium by electrolysis.
Metallurgy
ICSE 2022
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Answer
(a) Bauxite is heated under pressure with conc. caustic soda (NaOH) for 2 to 8 hours. Bauxite dissolves and forms sodium meta aluminate because of the amphoteric nature of aluminium, leaving behind insoluble impurities called red mud. Red mud consists of ferric oxide, sand, etc. which are removed by filtration.
(b) Aluminium oxide due to its great affinity for oxygen is a very stable compound. It is not reduced easily by common reducing agents like carbon, carbon monoxide and hydrogen. Hence, fused alumina can be reduced to aluminium only by electrolysis.
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