Question

In electrolysis of $A{l}_2{O}_3$ by Hall-Heroult process, _____________.

• A. Cryolite $N{a}_3\left[Al{F}_6\right]$ lowers the m.p. of $A{l}_2{O}_3$ and increases its electrical conductivity
• B. Al is obtained at cathode and probably $C{O}_2$ at anode
• C. Both (a) and (b) are correct
• D. None of the above

Answer 1

Answer: (C)

Both (a) and (b) are correct

The electrolysis of alumina by Hall and Heroult's process is carried by using a fused mixture of alumina and cryolite along with minor quantities of aluminum fluoride and fluorspar.The addition of cryolite and fluorpar increases the electrical conductivity of alumina and lowers the fusion temperature. At cathode Al(III) is reduced to Al metal. At anode, alumina reacts with fluorine to liberate oxygen. Oxygen reacts with carbon to form carbon dioxide.