Question

In the electrolysis of alumina, cryolite is added to ______________.

• A. lower the melting point of alumina.
• B. increase the electrical conductivity.
• C. minimize the anode effect.
• D. remove the impurities from alumina.

Answer 1

Answer: (A), (B)

The correct options are
A lower the melting point of alumina.
B increase the electrical conductivity.

The electrolysis of pure alumina faces some difficulties. Pure alumina is a bad conductor of electricity. The fusion temperature of pure alumina is about 2000${}^{\circ }$C and at this temperature when electrolysis is carried out on the fused mass, the metal formed vaporizes, as the boiling point of aluminium is 1800${}^{\circ }$C. These difficulties are overcome by using a mixture containing alumina, cryolite $(N{a}_3,Al{F}_6)$, and fluorspar $(Ca{F}_2,)$. But the addition of cryolite do not minimize the anode effect and do not remove the impurities from alumina.