Ncert Exercises & Solutions

In the extraction of aluminium by the Hall-Heroult process, purified ${Al}_{2} O_{3}$ is mixed with ${CaF}_{2}$ to:

a.	Lower the melting point of ${Al}_{2} O_{3}$
b.	Increase the conductivity of the molten mixture.
c.	Reduce ${Al}^{3 +}$ into $Al (s)$
d.	Act as a catalyst

Choose the correct option:
1. a and b
2. b and c
3. c and d
4. a and d

HINT: CaF₂ makes alumina a good conductor of electricity.

Explanation :

In the metallurgy of aluminium

{Al}_{2} O_{3}

is mixed with

{Na}_{3} {AlF}_{6}

and

{CaF}_{2}

which causes following affects.

(i) Lower the melting point of Al, O,

(ii) Increase the conductivity of molten mixture