Industrial Applications of Electrolysis - Extraction of Aluminium

  1. Figure above shows the illustration of the designed used to extract aluminium in industry by using electrolysis.
  2. In SPM, you need to know
    1. the electrolyte used
    2. the material used as anode and cathode
    3. the chemical reaction at anode and cathode
    4. why cryolite is added into molten bauxite in the process?

Electrolyte: 

Molten bauxite (Aluminium Oxide).

Al2O3 2Al3+ + 3O2-

Electrode:

Anode: Graphite
Cathode: Graphite

Chemical Reaction

Anode:
2O2-  O2 + 4e

At the anode, oxygen gas which also has commercial value is collected.

Cathode
Al3++ + 3e  Al

Note:
  1. The aluminium ions are attracted towards the graphite cathode.
  2. The ions is discharged and become molten aluminium metal.


Q & A

Q: Explain why cryolite is added into molten bauxite in the process?

A: To reduce the melting point of bauxite.

Q & A


Q: Explain why the carbon electrodes need to be replaced periodically.

A: 

  1. At the temperature of 980 °C, the oxygen burns the carbon anode.
  2. Also, this cell uses large quantities of electricity, and therefore needs cheap sources of power.



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