Question
In the electrolysis of alumina to obtain aluminium metal, cryolite is added mainly to
A.
lower the melting point of alumina
B.
dissolve alumina in molten cryolite
C.
remove the impurities of alumina
D.
increase the electrical conductivity
Answer :
lower the melting point of alumina
Solution :
Fused alumina $$\left( {A{l_2}{O_3}} \right)$$ is a bad conductor of electricity. Therefore, cryolite $$\left( {N{a_3}Al{F_6}} \right)$$ and fluorspar $$\left( {Ca{F_2}} \right)$$ are added to purified alumina which not only make alumina a good conductor of electricity but also reduce the melting point of the mixture to around $$1140\,K.$$