Explain with reasons:(a) In the electrolytic reduction of alumina, the

1.	Explain with reasons:(a) In the electrolytic reduction of alumina, the graphite anode is gradually consumed.(b) Roasting is carried out on sulphide ores and not on carbonate ores.(c) Carbon can reduce lead oxide but not aluminium oxide
Answer» (a) In the electrolytic reduction of alumina, the graphite (anode) is oxidized by oxygen to CO and further forms CO₂, so it is consumed and has to be replaced from time to time. 2C + O₂ ⟶2CO 2CO + O₂⟶2CO₂ (b) Roasting provides oxygen to convert metallic sulphides into metallic oxide and SO₂which takes place when heated in excess of air. Carbonate is converted into oxide by loss of CO₂ which takes place in the absence of air and when heated strongly. (c) Aluminium has a great affinity towards oxygen and so cannot be reduced by carbon or carbon monoxide or hydrogen whereas lead oxide can be easily reduced to metal lead by carbon. PbO + C ⟶ Pb + CO

Explain with reasons:(a) In the electrolytic reduction of alumina, the graphite anode is gradually consumed.(b) Roasting is carried out on sulphide ores and not on carbonate ores.(c) Carbon can reduce lead oxide but not aluminium oxide

Answer»

(a) In the electrolytic reduction of alumina, the graphite (anode) is oxidized by oxygen to CO and further forms CO₂, so it is consumed and has to be replaced from time to time.

2C + O₂ ⟶2CO

2CO + O₂⟶2CO₂

(b) Roasting provides oxygen to convert metallic sulphides into metallic oxide and SO₂which takes place when heated in excess of air.

Carbonate is converted into oxide by loss of CO₂ which takes place in the absence of air and when heated strongly.

(c) Aluminium has a great affinity towards oxygen and so cannot be reduced by carbon or carbon monoxide or hydrogen whereas lead oxide can be easily reduced to metal lead by carbon.

PbO + C ⟶ Pb + CO

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