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.

Industrial Applications of Electrolysis – Electroplating

  1. Electroplating is a process to coat an object with a thin protective layer of metal
  2. Electroplating is used to
    1. prevent corrosion
    2. improve the appearance of the objects
  3. In electroplating,
    1. the anode is the electroplating metal
    2. the cathode is the object to be electroplated
    3. the electrolyte must contain the ions of the plating meta

Example: Electroplate a Key with Copper


Electrolyte:
Copper(II) sulphate

CuSO4 —> Cu2+ + SO42-

Electrode:
Anode: Copper
Cathode: Object to be electroplated

Chemical Reaction
Anode:
Cu —> Cu2+ + 2e

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
Cu2+ —> Cu + 2e

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

  1. 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.
  2. In industry, electrolysis processed is used to purify copper, and the process is called electrolytic refining.

Electrolytic Refining of Copper

  1. Figure above shows the illustration of the apparatus setup to investigate electrolytic refining of copper.
  2. When electricity flows, the copper in the impure anode dissolves in the solution to form copper ions.
  3. Copper ions are then deposit on the cathode which consist of a piece of pure copper.
  4. In SPM, you need to know
    1. the electrolyte used
    2. the electrode for the impure and pure copper
    3. the reaction at anode and cathode

Electrolyte: 

Copper(II) sulphate

CuSO4 à Cu2++ SO42-

Electrode:

Anode: Impure copper
Cathode: Pure copper

Chemical Reaction

Anode:
Cu —> Cu2+ + 2e
In anode, the copper atoms from the electrode are ionised to form copper(II) ions.
Cathode
Cu2+ —> Cu + 2e
In cathode, the copper ions are discharged to form copper atom and then deposit on the surface of the key

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.