MetallurgyHard
Question
In electrolysis of Al2O3 by Hall-Heroult process :
Options
A.cryolite Na3[AlF6] lowers the melting point of Al2O3 and increases its electrical conductivity.
B.Al is obtained at cathode and probably CO2 at anode
C.both (A) and (B) are correct
D.none of the above is correct
Solution
Na3[AlF6] → 3NaF + AlF3
NaF and AlF3 both are ionic compounds and so ionise to give ions. This increases the electrical conductivity and lowers the melting point of Al2O3.
At cathode : Al3+ (melt) + 3e- → Al.
At anode : C(s) + O2- (melt) → CO (g) + 2e- ; C(s) + 2O2- (melt) → CO2 (g) + 4e-.
NaF and AlF3 both are ionic compounds and so ionise to give ions. This increases the electrical conductivity and lowers the melting point of Al2O3.
At cathode : Al3+ (melt) + 3e- → Al.
At anode : C(s) + O2- (melt) → CO (g) + 2e- ; C(s) + 2O2- (melt) → CO2 (g) + 4e-.
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