Wednesday, July 6, 2011

Chemistry Form 4: Chapter 6 - Extraction of Aluminium From its Ore

The ores of aluminium is called bauxite. Bauxite is a composition of aluminium oxide, (Al2O3).

The position of aluminium in the reactivity series indicates that, it could not be extracted by reducing the oxide using carbon or carbon monoxide. Electrolysis of molten aluminium oxide ("alumina") will, however, give aluminium and oxygen.

A = carbon anode       B = molten aluminium    
C = molten aluminium oxide and cryolite     D = carbon cathode  
  • The function of cryolite is to lower the melting point of aluminium oxide.
  • Aluminium metal forms at the cathode electrode and sinks to the bottom of the tank, where it is tapped off.
  • Oxygen forms at the anode electrodes. This oxygen reacts with the carbon of the anode electrodes, forming carbon dioxide, and they gradually burn away. Consequently, the anode electrodes have to be replaced frequently.

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