Metals

• Metals can be extracted from molten compounds using electrolysis
• Electrolysis is used if the metal is too reactive to be extracted by reduction with carbon or if the metal reacts with carbon
• 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)
• Aluminium has a vary high melting point so cryolite is used to lower it
• The electrodes need to be replaced because the oxygen reacts with the carbon electrode to form carbon dioxide
• When separating aluminium oxide

  • At the cathode aluminium is reduced - $Al^{3+} +$$3e^- \rightarrow Al$
  • At the anode the oxygen is oxidised - $2O^{2-} \rightarrow O_2 +$$4e^-$