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NEET 2012

Exam: NEET
Year: 2012
Subject: Chemistry
Chapter: General Principles and Processes of Isolation of Metals

NEET 2012 · Chemistry · General Principles and Processes of Isolation of Metals

Aluminium is extracted from alumina (Al_2 O_3) by electrolysis of a...

Aluminium is extracted from alumina

\left(\mathrm{Al}_2 \mathrm{O}_3\right)

by electrolysis of a molten mixture of

Options

A $\mathrm{Al}_2 \mathrm{O}_3+\mathrm{HF}+\mathrm{NaAlF}_4$
B $\mathrm{Al}_2 \mathrm{O}_3+\mathrm{CaF}_2+\mathrm{NaAlF}_4$
C $\mathrm{Al}_2 \mathrm{O}_3+\mathrm{Na}_3 \mathrm{AlF}_6+\mathrm{CaF}_2$
D $\mathrm{Al}_2 \mathrm{O}_3+\mathrm{KF}+\mathrm{Na}_3 \mathrm{AlF}_6$

Correct answer

C. $\mathrm{Al}_2 \mathrm{O}_3+\mathrm{Na}_3 \mathrm{AlF}_6+\mathrm{CaF}_2$

Step-by-step solution

Alumina,

\mathrm{Al}_2 \mathrm{O}_3

, is a bad conductor of electricity and has very high melting point, so before subjecting to electrolysis, it is mixed with fluorspar

\left(\mathrm{CaF}_2\right)

and cryolite \left(\mathrm{Na}_3 \mathrm{AlF}_6\right), which lower its melting point and make it more conducting.

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