Electrolysis

• The process of electrolysis is when an electric current is passed through an electrolyte (a liquid or solution that contains ions, so can therefore conduct electricity). This causes the ions to move to the electrodes, where they form pure elements
• Solid ionic compounds cannot conduct electricity as the ions cannot move. To undergo electrolysis, they must be molten or dissolved so that the ions can move
• The positive metal ions are attracted to the negative cathode, where they will gain electrons to form the pure metal
• The negative non-metal ions are attracted to the positive anode, where they lose electrons and become the pure non-metal
• Solid ionic compounds can undergo electrolysis when dissolved in water. It requires less energy to dissolve ionic compounds in water than to melt them, however in electrolysis of solutions the pure elements are not always formed as water can also undergo ionisation
• In electrolysis of a solution, if the non-metal contains oxygen then oxygen will be produced at the anode as the negative water ions formed from the ionisation of water are attracted to the anode. They lose electrons and form oxygen gas. If the non-metal ion is a halogen, the halogen gas is formed at the anode
• In electrolysis of a solution, a metal that is more reactive than hydrogen will lead to hydrogen gas being formed at the cathode, and the metal ions remain in the solution
• Electrolysis can be used to extract metals from their ionic compound if the metal is more reactive than carbon
• Aluminium is extracted from aluminium oxide using electrolysis. The aluminium oxide is mixed with cryolite to lower the melting point and the mixture is heated until molten. The mixture undergoes electrolysis, and the pure aluminium is formed at the cathode and oxygen is formed at the anode