Question

Answer the following questions with respect to the electrolytic process in the extraction of aluminium:
Explain why powdered coke is sprinkled over the elecrolytic mixture.

Answer 1

The molten electrolyte is covered with layer of powder coke to prevent oxidation and loss of heat due to radiation.
Note:
With respect to the electrolytic process in the extraction of aluminium, the components of the electrolyte other than pure alumina $\left(A{l}_2{O}_3\right)$ (2-8%) are synthetic cryolite $\left(N{a}_{3}Al{F}_6\right)$ (80-85%), $Al{F}_3$ (5-7%) and fluorspar $\left(Ca{F}_2\right)$ (5-7%).
The addition of cryolite and fluorspar not only makes alumina a good comductor of electricity but also lowers the fusion temperature to around 1140 K.