Write the role of the following:
(i) CO in the purification of Nickel.
(ii) Graphite rod in the electrometallurgy of aluminium.
CO readily react with nickel at low temperatures of 50oC- 60oC to give Ni(CO)4 which is gaseous in nature, hence nickel vaporises, leaving behind impurities. This gas when heated to 220oC-250oC CO escapes leaving behind nickel of very high purity. The reaction between nickel and carbon monoxide occurs readily and reversibly, hence CO lays a very important role in purification of nickel.
(ii) In the electrometallurgy of aluminium, graphite is used as anode and graphite lined iron rod is used as cathode. The oxygenformed at anode reacts with carbon to form CO and CO2. Otherwise the oxide will react with the pure aluminium formed at cathode to give Al2O3again, which is unwanted.
Anode:
Cathode: 
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