Question

Electrolytic reduction of alumina to aluminium by Hall-Heroult process is carried out _______________.

• A. in the presence of NaCl
• B. in the presence of fluorite
• C. in the presence of cryolite which forms a melt with lower melting temperature
• D. in the presence of cryolite which forms a melt with higher melting temperature

Answer 1

The correct option is C in the presence of cryolite which forms a melt with lower melting temperature

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 $\left(Ca{F}_2\right)$ which forms a melt with lower melting temperature.