A-LevelChemistryElectrochemistry9701/12 · Oct/Nov 2013 · Q11 Mark
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?
AAl2O3 is covalent, and AlF3⁻ ions interact with it to produce Al³⁺ ions which can be discharged at the cathode.
BCryolite is a base, forming NaAlO2 with bauxite, enabling aluminium to be discharged at the anode.
CCryolite minimises the release of O²⁻ ions at the graphite anodes, which are otherwise burnt away to CO.
DCryolite reduces the melting point of the bauxite.
✓ Correct answer
D: Cryolite reduces the melting point of the bauxite.
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