Why is the electrolytic reduction used for metals like aluminium?

The electrolytic reduction is used for metals like aluminium because they are too reactive to be extracted by reduction with carbon.

Aluminium is a highly reactive metal that is found in the Earth's crust as an ore called bauxite. Bauxite is a type of aluminium oxide, which is a compound of aluminium and oxygen. The process of extracting aluminium from its ore involves two main steps: purification of bauxite to obtain pure aluminium oxide, and then reduction of aluminium oxide to aluminium.

The reduction of aluminium oxide to aluminium is not possible using carbon because aluminium is more reactive than carbon. This means that aluminium has a stronger affinity for oxygen than carbon does, so it cannot be displaced from its oxide by carbon. Instead, a process called electrolytic reduction is used. This involves passing an electric current through the aluminium oxide to break it down into its constituent elements: aluminium and oxygen.

In the electrolytic reduction process, the aluminium oxide is dissolved in a substance called cryolite, which lowers the melting point of the aluminium oxide and increases the conductivity of the solution. The electric current is then passed through this solution, causing the aluminium oxide to break down. The aluminium ions gain electrons (are reduced) at the cathode to form aluminium atoms, while the oxygen ions lose electrons (are oxidised) at the anode to form oxygen gas.

This process is energy-intensive, but it is the only practical way to extract aluminium due to its high reactivity. It is also used for other highly reactive metals, such as sodium and potassium, for the same reason.