Question

In Hall-Heroult process, how much carbon anode is burnt away to produce each $1kg$ of aluminium?

• A. $0.3kg$
• B. $0.5kg$
• C. $1kg$
• D. $0.1kg$

Answer 1

Answer: (B)

Reaction at cathode:
$A{l}^{3+}+3e^{-}\to Al$ .... (i)
Reaction at anode:
$C+O^{2-}\to CO+2e^{-}$ .....(ii)
$C+2O^{2-}\to C{O}_2+4e^{-}$ ..... (iii)
By performing $2\times (i)+$ (ii) $+$ (iii):
$2A{l}^{3+}+\underset{(2\times 12kg)}{2C+3O^{2-}}\to \underset{(2\times 27kg)}{2Al+CO}+C{O}_2$
$2\times 27kg$ of Al is required $=2\times 12kg$ of carbon
$1kg$ of Al is required $=\frac{2\times 12}{2\times 27}kg$ of carbon $=0.5kg$.