Choosing the Method of Extraction

  • The position of the metal on the reactivity series determines the method of extraction.
  • Higher placed metals (above carbon) have to be extracted using electrolysis as they are too reactive and cannot be reduced by carbon.
  • Lower placed metals can be extracted by heating with carbon which reduces.
  • The process is very expensive as large amounts of energy are required to melt the ores and produce the electrical current.
  • The reactivity series of metals is shown below with the corresponding method of extraction.

Metal Extraction Table, IGCSE & GCSE Chemistry revision notes

The Extraction of Aluminium

Extraction of Aluminium by Electrolysis

Extraction of Aluminium by electrolysis, IGCSE & GCSE Chemistry revision notes

Diagram 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 reduces expenses considerably making the process more efficient.

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 which is a major expense.

The overall equation is:

2Al2O3(l) ⟶ 4Al(l) + 3O2(l)

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 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.

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Morgan Curtin Chemistry

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.