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What is the role of graphite rod in the electrometallurgy in aluminium?

Answer»

Solution :In the electrometallurgy of alumina, a fused mixture of alumina, CRYOLITE and flourspar `(CaF_2)` is electrolysed using praphite as anode and graphite LINED iron as cathode. During electrolysis, Al is liberated at the cathode while CO and `CO_2` are liberated at the anode. The relevant equations are as under :
At cathode : `Al^(3)(" melt ") to Al (l)`
At anode : `C(s)+O^(2-) (" melt ") to CO_(2) (g) + 2e^(-)`
`C(s) +2O^(2-) (" melt ") to CO_(2) (g) +4e^(-)`.
Oxygen evolved at the anode burns, the anode meterial (graphite).
If instead of graphite, some other METAL is used as the anode, then `O_2` libetated will OXIDISE the metal of the electrode. Since graphite is much CHEAPER than any metal, therefore, graphite is used as the anode.


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