The process of electrolysis
● When an ionic substance is melted or dissolved, the ions are free to move about
within the liquid or solution.
● Passing a current through substances that are molten or solution means that the
solution can be broken down into elements. This is electrolysis, and the
substance being broken down is the electrolyte.
● During electrolysis, positively charged ions move to the negative electrode
(cathode), and negatively charged ions move to the positive electrode (anode).
● Ions are discharged at the electrodes producing elements
Electrolysis of molten ionic compounds
● When a simple ionic compound (e.g lead bromide) is electrolysed in the molten
state using inert electrodes, the metal (lead) is produced at the cathode and the
non-metal (bromine) is produced at the anode
● this is because the metal is the positive ions and the non-metal is the negative
ions
Using electrolysis to extract metals
● Metals that are more reactive than carbon (e.g aluminium), so too reactive to be
extracted by reduction with carbon, are extracted by electrolysis of molten
compounds.
● Large amounts of energy are used in the extraction process to melt the
compounds and to produce the electrical current.
● Aluminium is manufactured by the electrolysis of a molten mixture of aluminium
oxide and cryolite using carbon as the positive electrode (anode).
o Aluminium oxide has a very high melting point, so it would be too
expensive to melt it, which is why it is mixed with cryolite
o the positive electrodes need to be continually replaced because oxygen is
formed, which reacts with the carbon of the positive electrodes, forming
carbon dioxide, and they gradually burn away
● Metals that react with carbon can be extracted by electrolysis as well