Industrial Applications of Electrolysis

Extraction of Metals

  1. Diagram below shows the methods of extraction for different metals.
  2. Metals which are less reactive than carbon in reactivity series are extracted from their ore by displacement reaction using carbon.
  3. Copper and mercury can be extracted from their ore by burning directly in air.
  4. Silver (Ag) and gold (Au) need no extraction because they exist as element in nature.
  5. Those metals which are more reactive than carbon are extracted by electrolysis.
Extraction of Sodium

 

  1. Figure above shows the illustration of the designed used to extract sodium 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

Electrolyte

Molten sodium chloride

NaCl —> Na+ + Cl–

Electrode:

Anode: Graphite
Cathode: Iron

Chemical Reaction

Anode:

2Cl– —> Cl2 + 2e

The negative chloride ions are attracted to the anode and then discharged to form chlorine gas.

Cathode

Na+ + e —> Na

Note:

  1. The sodium ions are discharged to form sodium atom.
  2. Due to high temperature, the sodium metal formed is in molten form.
  3. Metal sodium have lower density. Therefore it moves upward and been collected.

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.