A-LevelChemistryElectrochemistryOct/Nov 2013Paper 1 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
The correct answer is D: Cryolite reduces the melting point of the bauxite.
📋 Examiner Report & Trap Analysis
Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...
🎯 Mark Scheme Breakdown
Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.
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