Question

Aluminium is extracted from alumina (Al₂O₃) by electrolysis of a molten mixture of

(a) Al₂O3 + HF + NaAlF₄

(b) Al₂O₃ + CaF₂ + NaAlF₄

(c) Al₂O₃ + Na₃AlF₆ + CaF₂

(d) Al₂O₃ + KF + Na₃AlF₆

Answer 1

Correct option (c) Al₂O₃ + Na₃AlF₆ + CaF₂

Explanation :

Electrolytic mixture contains alumina (Al₂O₃), cryolite (Na₃AlF₆) and fluorspar (CaF₂) in the ratio of 20 : 40 : 20. Due to presence of these conductivity of alumina increases and fusion temperature decreases from 2000°C to 900°C.