CIE IGCSE Chemistry

Revision Notes

5.2 Industrial Applications

Extended Only

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)

Explanation:

  • 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

Author: Morgan

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.
Close

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now