Electrolysis

• Electrolysis is the process of using electricity to extract elements from a compound.
• Anode is the positive electrode.
• Cathode is the negative electrode.
• An electrolyte is a liquid or solution that contains ions and so can conduct electricity.
• Metals are formed at the cathode.
• Non-metals are formed at the anode.
• Ionic substances are electrolysed by melting or dissolving them and passing a current through them.
• Solid ionic substances can't be electrolysed because they can't conduct electricity as the ions cannot move.
• Metal is not produced at the cathode when the metal is more reactive than hydrogen.
• Halogen gas is produced at the anode in the electrolysis of a metal halide solution.
• Oxygen is produced at the anode in the electrolysis of a metal sulfate solution.
• Half equation for the ionisation of water:

  H2O (l) -> H+ (aq) + OH- (aq)
• Metals that are more reactive than carbon are extracted from ionic compounds by electrolysis.
• In the electrolysis of aluminium oxide, aluminium oxide is mixed with cryolite to lower the melting point.
• In the electrolysis of aluminium oxide, the anodes are made of graphite.
• In the electrolysis of aluminium oxide, the anodes need to be replaced because they react with the oxygen being formed.