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  4. In the electrolysis of alumina, a layer of powdered coke is spread on the surface of the electrolyte in the cell

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Q. In the electrolysis of alumina, a layer of powdered coke is spread on the surface of the electrolyte in the cell

General Principles and Processes of Isolation of Elements

Solution:

In the electrolysis of fused alumina, cryolite and fluorspar, oxygen is liberated at the anode reacts with carbon anode to form $CO$. The hot $CO$ comes in contact with air and burn spontaneously giving $CO_{2}$. Consequently, the anodes get corroded and have to be replaced from time to time. However, the layer of powdered coke spread at the surface of molten electrolyte slows down the consumption of the anode and prevent heat loss due to radiation