1.4.7 Industrial Applications of Electrolysis
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
Electrode:
Anode: Graphite
Cathode: Iron
Chemical Reaction
Anode:
The negative chloride ions are attracted to the anode and then discharged to form chlorine gas.
Cathode
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).
Electrode:
Anode: Graphite
Cathode: Graphite
Chemical Reaction
Anode:
At the anode, oxygen gas which also has commercial value is collected.
Cathode
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.
Industrial Applications of Electrolysis - Electroplating
- Electroplating is a process to coat an object with a thin protective layer of metal
- Electroplating is used to
- prevent corrosion
- improve the appearance of the objects
- In electroplating,
- the anode is the electroplating metal
- the cathode is the object to be electroplated
- the electrolyte must contain the ions of the plating meta
Example: Electroplate a Key with Copper
Electrolyte:
Copper(II) sulphate
Electrode:
Anode: Copper
Cathode: Object to be electroplated
Chemical Reaction
Anode:
In anode, the copper atoms from the electrode are ionised to form copper(II) ions.
Note: The anode is then made of the metal we wish to plate with (copper), and the electrolyte needs to be a solution of a salt of this metal (copper(II) sulphate).
Cathode
In cathode, the copper ions are discharged to form copper atom and then deposit on the surface of the key
Note: we need to make the cathode the object for plating
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Electrolysis – Plating
Industrial Applications of Electrolysis - Purifying of Copper
- Copper is a good electrical conductor and is used extensively to make electrical wiring and components. However, the presence of impurity in copper can reduce its electrical conductivity.
- In industry, electrolysis processed is used to purify copper, and the process is called electrolytic refining.
Electrolytic Refining of Copper
- Figure above shows the illustration of the apparatus setup to investigate electrolytic refining of copper.
- When electricity flows, the copper in the impure anode dissolves in the solution to form copper ions.
- Copper ions are then deposit on the cathode which consist of a piece of pure copper.
- In SPM, you need to know
- the electrolyte used
- the electrode for the impure and pure copper
- the reaction at anode and cathode
Electrolyte:
Copper(II) sulphate
Electrode:
Chemical Reaction
Note: Impurities in the copper do not dissolve, and instead fall off the anode as anode sludge. At the cathode, the copper ions are deposited as pure copper metal.