Question

The major role of Fluorspar ($Ca{{F}_{2}}$) which is added in small quantity in the electrolytic reduction of alumina dissolved in fused cryolite ($N{{a}_{3}}Al{{F}_{6}}$) is:
I. To act as a catalyst
II. To make the fused mixture very conduction
III. To lower the temperature of melting
IV. To decrease the rate of oxidation of carbon at the anode
(A) I, II
(B) II, III
(C) I, II, III
(D) III, IV

Answer 1

Hint: Fluorspar can be used as a flux in certain mixtures. Fluorspar has three ions in its structure so we can expect the change in the conductance of the solution due to its presence. This whole process is called the Hall-Heroult process.

Complete step by step answer:
In the electrolytic reduction of alumina, fluorspar is added in small quantities with cryolite. This process of reduction of alumina is called the Hall-Heroult process.
- Now, we need alumina in molten state in order to continue this electrolysis. So, we need to give high temperatures to the reaction system. Then , it was discovered that if we add some particular compound to the mixture then it decreases the melting point of the mixture. This compound is called flux.
- So, $Ca{{F}_{2}}$ is also used here to decrease the melting point of the mixture that is going to undergo electrolysis.
- Alongside Cryolite, Fluorspar also increases the conductivity of the solution and as a result it makes it easy to complete the electrolysis of alumina.
- Fluorspar does not have any effect on the oxidation of carbon at anode.

Note: Remember that $Ca{{F}_{2}}$ do not have any catalytic effect at all in this process. Remember the roles of Cryolite and Fluorspar in this process. Cryolite is used as a solvent for alumina in this reaction. Fluorspar can also be called Calcium fluoride.