9701 MCQ Solution 49

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Question 49: [Physical > Electrochemistry]
At the age of 17 , in a woodshed in Ohio, Charles Martin Hall discovered the commercial process for the production of aluminium metal by the electrolysis of a mixture of bauxite, Al2O3, and cryolite, Na3AlF6.
What is the main purpose of the cryolite?
A Al2O3 is covalent, and AlF63- ions interact with it to produce Al3+ ions which can be discharged at the cathode.
B Cryolite is a base, forming NaAlO2 with bauxite, enabling aluminium to be discharged at the anode.
C Cryolite reduces the melting point of the bauxite.
D Cryolite minimises the release of O2- ions at the graphite anodes, which are otherwise burnt away to CO.
Reference: Past exam paper -June 2003 Paper 1 Q9


Solution 49:
Answer: C.

Cryolite is used to reduces the melting point of the bauxite because without the cryolite the melting point for the extraction of aluminium would be very high.

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