Very reactive metallic elements are extracted from ores by electrolysis
- Because they are higher up in the reactivity series than carbon, they cannot be displaced from their oxides by carbon
The usual source of aluminium is the ore, bauxite.
This is treated chemically to leave a white aluminium oxide powder, \(Al_2O_3\), commonly known as alumina
Alumina has a very high melting point .
- Therefore, in order for it to be electrolysed, it has to be dissolved in molten cryolite
- Acts as a solvent for the alumina
- Cryolite also has a high melting point
Cathode:
- Attracts Al ions where they gain electrons to form aluminium metal
- \(Al^{3+}+3e^- \rightarrow Al\)
Anode:
- Attracts oxide ions
- Lose electrons and form oxygen gas
- Oxygen gas reacts with carbon anodes, so they have to be replaced from time to time
- \(2O^- \rightarrow O_2 + 4e^-\)