CIE IGCSE Chemistry

Revision Notes

5.2 Industrial Applications

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Manufacture of Aluminium, Chlorine, Hydrogen & Sodium Hydroxide

Extraction of aluminium

  • The Earth’s Crust contains metals and metal compounds such as Gold, Iron Oxide and Aluminium Oxide, but when found in the Earth, these are often mixed with other substances
  • To be useful, the metals have to be extracted from their ore through processes such as electrolysis, using a blast furnace or by reacting with more reactive material
  • Metals which lie above carbon have to be extracted by electrolysis as they are too reactive

Reactivity series & extraction of metals

Reactivity Series and Extraction of Metals table, IGCSE & GCSE Chemistry revision notes


Extraction of aluminium by electrolysis


Extraction of Aluminium by electrolysis, IGCSE & GCSE Chemistry revision notesDiagram showing the extraction of aluminium by electrolysis


Raw Materials: Aluminium Ore (Bauxite)


  • The Bauxite is first purified to produce Aluminium Oxide Al2O3
  • Aluminium Oxide has a very high melting point so it is first dissolved in molten cryolite producing an electrolyte with a lower melting point, as well as a better conductor of electricity than molten aluminium oxide. This also reduces expense considerably
  • The electrolyte is a solution of aluminium oxide in molten cryolite at a temperature of about 1000 °C. The molten aluminium is siphoned off from time to time and fresh aluminium oxide is added to the cell. The cell operates at 5-6 volts and with a current of 100,000 amps. The heat generated by the huge current keeps the electrolyte molten
  • A lot of electricity is required for this process of extraction, this is a major expense

Reaction at the Negative Electrode:

The Aluminium melts and collects at the bottom of the cell and is then tapped off:

Al3+    +    3e-    →    Al

 Reaction at the Positive Electrode:

2O2-    –    4e    →    O2

Some of the Oxygen Produced at the positive electrode then reacts with the Graphite (Carbon) electrode to produce Carbon Dioxide Gas:

C (s)    +    O2 (g)    →    CO2 (g)

*This causes the carbon anodes to burn away, so they must be replaced regularly.


Manufacture of chlorine, hydrogen and sodium hydroxide

  • Brine is a concentrated solution of aqueous sodium chloride
  • When electrolysed it produces chlorine, hydrogen and sodium hydroxide
  • The electrolyte is concentrated sodium chloride which contains the following ions: H+, Cl and OH
  • The H+ ions are discharged at the cathode as hydrogen gas
  • The Cl ions are discharged at the anode as chlorine gas
  • The Na+ and OH ions remain behind and form the NaOH solution


Electrolysis Brine, IGCSE & GCSE Chemistry revision notesDiagram showing the products of the electrolysis of brine

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Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.

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