Extraction of Metals
- Diagram below shows the methods of extraction for different metals.
- Metals which are less reactive than carbon in reactivity series are extracted from their ore by displacement reaction using carbon.
- Copper and mercury can be extracted from their ore by burning directly in air.
- Silver (Ag) and gold (Au) need no extraction because they exist as element in nature.
- Those metals which are more reactive than carbon are extracted by electrolysis.
Extraction of Sodium
- Figure above shows the illustration of the designed used to extract sodium in industry by using electrolysis.
- In SPM, you need to know
- the electrolyte used
- the material used as anode and cathode
- 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:
- The sodium ions are discharged to form sodium atom.
- Due to high temperature, the sodium metal formed is in molten form.
- Metal sodium have lower density. Therefore it moves upward and been collected.
Extraction of Aluminium
- Figure above shows the illustration of the designed used to extract aluminium in industry by using electrolysis.
- In SPM, you need to know
- the electrolyte used
- the material used as anode and cathode
- the chemical reaction at anode and cathode
- 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:
- The aluminium ions are attracted towards the graphite cathode.
- 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:
- At the temperature of 980 °C, the oxygen burns the carbon anode.
- Also, this cell uses large quantities of electricity, and therefore needs cheap sources of power.