General Principles And Processes Of Isolation Of Elements

Question
CBSEENCH12009907

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

Solution

In electrolysis of aluminium, graphite is used as the anode and graphite-lined iron is used as the cathode. During the electrolysis, Al is liberated at the cathode, while CO and CO2 are liberated at the anode, according to the following equation.

Cathode: Al3+ +3e- → Al

Anode: C + O2- → CO +2e-

            C + 2O2- → CO2 +4e-
 
If a metal is used instead of graphite as the anode, then O2 will be liberated. This will not only oxidise the metal of the electrode, but also convert some of the Al liberated at the cathode back into Al2O3. Therefore, graphite is used for preventing the formation of O2 at the anode. 

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