• It is the breakdown of an electrolyte- ionic compound, molten or aqueous solution- by passing an electric current
  • This is possible due to the presence of mobile electrons


  • Aqueous solution of ionic substance or molten ionic salt
  • Conducts electricity due to the presence of mobile ions


Components of Electrolysis Definition
Electrodes Metal or graphite rods that aid the flow of electricity in and out of the electrolyte
1. Anode: Positive electrode
2. Cathode: Negative ElectrodeReactive electrodes take part in the reaction while inert electrodes do not
Anion Negatively charged ion that moves to anode
Cation Positively charged ion that moves to cathode


  • Reduction of positive cations happens at the cathode
  • Oxidation of negative anions happens at the anode


For example:

  • At the anode: 2Cl → Cl2 + 2e
  • At the cathode: 2H+ + 2e → H2

Examples of Electrolysis

Electrolyte At cathode At anode
Molten lead (II) bromide Lead Bromine
Concentrated hydrochloric acid Hydrogen Chlorine
Concentrated aqueous sodium chloride Hydrogen Chlorine
Dilute sulfuric acid Hydrogen Oxygen

Voltaic Cell

  • Used to produce electrical energy from chemical energy
  • The electrodes are made from metals with different reactivity

1.Negative electrode: More reactive metal, ex. Zinc

  • Positive electrode: Less reactive metal, ex. Iron
  • Electrolyte is a strong acid, ex. sulfuric acid
  • The negative electrode loses electrons; these flow through the simple circuit to the positive electrode to produce voltage. This is measured on the attached voltmeter.

Note: The greater the difference in reactivity, the greater voltage produced


The process of coating the surface of a metal (more reactive) with another metal (less reactive) using electrolysis

  • Components:
    • Anode: pure metal being used to electroplate the object
    • Cathode: object being electroplated
    • Electrolyte: aqueous solution of the soluble salt of pure metal (same as anode)
  • Used to:
    • Prevent corrosion
    • Enhance appearance
Conductors Insulators
Allow the passage of electrical charge Resist the passage of electrical charge
Aluminum [low density, non-corrosive, cheaper than copper]: used in electricity cables with a steel core and plane bodies Plastics for casing in wires
Copper [malleable]: used in electrical wires Ceramics used to support cables in electricity pylons

Electrolytic purification of metals

  • Cathode: thin strip of pure metal
  • Anode: impure metal
  • Electrolyte: Aqueous Salt Solution of metal


Purification of copper

Impure copper as the anode and pure copper as the cathode; the aqueous copper (II) sulfate helps the copper ions move from the anode to the cathode. Here the ions gain electrons and become copper atoms, making the pure copper cathode thicker.

  • Reaction at Anode: Cu – 2e Cu2+ (mass decreases)
  • Reaction at Cathode: Cu2+ + 2e Cu (mass increases)

Electrolytic purification of copper

  • Electrolyte: aq copper(ii)sulphate
  • Cathode: thin strip of pure copper
  • Anode: impure metal
  • Copper ions from the solution lose thier charge and copper is deposited at the cathode, mass increases
  • Copper atoms lose their valency electrons and go into the solution as ions at the anode, mass decreases

Electroplating is done to coat a metal with another metal to improve its appearance or to improve its resistance to corrosion. The metal used for plating is used as the anode and the object to be electroplated acts as the cathode. The electrolyte used is the salt solution of the metal used for

Copper metal acts as the anode as it is used to plate the object. The electrolyte used is a salt solution of its salt (copper(II) sulfate solution) and the object to be plated acts as the cathode.

At the anode, the copper atoms are oxidised into Cu2+ ions, which enter the electrolyte. At the cathode, Cu2+ ions are discharged and deposited on the object, plating it with
copper metal.


Extraction of Aluminum

  • The main ore of aluminum is bauxite – high m.p.
  • Aluminum (III) oxide (alumina) is dissolved in molten cryolite (Na3AlF6) – this mixture has a lower m.p. (industrially preferred)

  • During electrolysis aluminum ( Al3+ + 3e-  → Al ) is produced at the carbon cathode and oxygen ( 2O2- – 4e-   → O2 ) at the carbon anode.
  • Due to the high temp. the oxygen reacts with the carbon in the graphite anode to form CO2 and so anode has to be periodically replaced


Electrolysis of Brine

  • Brine is concentrated aqueous NaCl solution
  • Ions present: Na+, H+, Cl and OH

At the anode At the cathode
Made of titanium Made of steel
Cl ions; Chlorine gas Hydrogen cations reduced to H2 molecules
Unreacted ions (Na+, H+ and OH) move through porous membrane due to difference in liquid pressure
Left Na+ and OH which form aqueous sodium hydroxide

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