- Home
- Standard 12
- Chemistry
Aluminium is extracted from alumina $(Al_2O_3)$ by electrolysis of a molten mixture of:
$Al_2O_3 + Na_3AlF_6 + CaF_2$
$Al_2O_3 + KF + Na_3AlF_6$
$Al_2O_3 + HF + NaAlF_4$
$Al_2O_3 + CaF_2 + NaAlF_4$
Solution
The electrolysis of pure alumina faces some difficulties. Pure alumina is a bad conductor of electricity.
The fusion temperature of pure alumina is about $2000^{\circ} \mathrm{C}$ and at this temperature when electrolysis is carried out on the fused mass, the metal formed vaporizes, as the boiling point of aluminum is $1800^{\circ} \mathrm{C}$.
These difficulties are overcome by using a mixture containing alumina $\left(\mathrm{Al}_{2} \mathrm{O}_{3}\right)$, cryolite $\left(\mathrm{Na}_{3} \mathrm{AlF}_{6}\right),$ and fluorspar $\left(\mathrm{CaF}_{2}\right)$
Therefore, the correct option is $\mathrm{D}$
