Why are sodium and fluoride ions not discharged during electrolysis of aluminium oxide
Sodium and fluoride ions are not discharged during the electrolysis of aluminium oxide because they are more reactive than aluminium. This means that they would be preferentially discharged at the cathode before aluminium ions if they were present in the electrolyte. However, in the case of the Hall-Héroult process for extracting aluminium from aluminium oxide, the electrolyte used is a molten mixture of cryolite (Na3AlF6) and aluminium oxide (Al2O3), so the sodium and fluoride ions react with the aluminium oxide to form insoluble compounds and do not participate in the electrolysis reaction. This allows for the selective discharge of aluminium ions at the cathode to produce pure aluminum metal.
