Why aluminium needs electrolysis
Aluminium is more reactive than carbon, so carbon cannot extract it by reducing aluminium oxide. Aluminium is manufactured by electrolysis of aluminium oxide dissolved in molten cryolite.
Lesson 4.12 · AQA Combined Science
Extracting aluminium
Why add cryolite?
The mixture melts at a lower temperature than pure aluminium oxide. Less energy is needed to keep it molten, reducing cost. The process still needs much energy for heating and electrical current.
Where do the products form?
Aluminium forms at the negative cathode and collects at the bottom. Oxygen forms at the positive carbon anodes. Oxygen reacts with the hot carbon to form carbon dioxide, so the carbon anodes wear away and must be replaced regularly.
Remember
Cryolite lowers the melting temperature. Oxygen reacts with carbon anodes, so they need replacing.
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