Reason for use of fused cryolite (Na3AlF6) along with fluorspar (CaF2) which is added to the electrolytic mixture containing pure alumina.

Reason for use of fused cryolite (Na3AlF6) along with fluorspar (CaF2) which is added to the electrolytic mixture containing pure alumina.

1. Electrolysis requires the electrolyte to be in liquid state.
2. Alumina has a very high melting point (> 2000ºC).
3. So, electrolysis of alumina is carried out at a much lower temperature by dissolving it in molten cryolite (Na3AlF6)
4. Cryolite has a lower melting point than alumina. The melting point of solution of alumina in cryolite is lower than cryolite.
5. It is further lowered by adding some fluorspar (CaF2).

6. Thus, the solution of alumina in cryolite with added fluorspar is electrolysed at about 1000ºC.

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