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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Complete the table given below which refers to the Laboratory preparation of Ammonia gas:
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(a) Carbon from cane sugar and concentrated sulphuric acid.
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(c) Ammonium sulphate from ammonium hydroxide and sulphuric acid.
State the observation for the following:
(a) Dry ammonia gas reacts with oxygen in the presence of a catalyst.
(b) Excess chlorine gas reacts with ammonia gas.
(c) Carbon reacts with hot concentrated nitric acid.
State one use of the given alloys:
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(b) Duralumin