Question

Describe the following.
(i) The role of cryolite in electro-metallurgy of aluminium.
(ii) The role of carbon monoxide in the refining of crude nickel.

Answer 1

I) Cryolite ($N{a}_{3}Al{F}_6$) has two roles in the metallurgy of aluminium:

1. To decrease the melting point of the mixture from 2323 K to 1140 K.

2. To increase the electrical conductivity of $A{l}_2{O}_3$.

II) Nickel is refined by Mond's process. In this process, nickel is heated in the presence of carbon monoxide to form nickel tetracarbonyl, which is a volatile complex.

$Ni+4CO\to Ni(CO{)}_4$

Then, the obtained nickel tetracarbonyl is decomposed by subjecting it to a higher temperature (450 - 470 K) to obtain pure nickel metal.

$Ni\left(CO{)}_4\right)\stackrel{450-470K}{\to }Ni+4CO$