Electrolysis

• When an ionic compound is melted or dissolved in water, the ions are free to move about the liquid or solution
• Liquids and solutions that are able to conduct electricity are called electrolytes
• Passing an electric current through electrolytes

  Causes the ions to move to the electrodes
• Cathode


  Negative electrode
• Anode


  Positive electrode
• Cations (positive ions)


  Go to the negative electrode (cathode)
• Anions (negative ions)


  Go to the positive electrode (anode)
• Electrolysis


  Ions are discharged at the electrodes producing elements
• Cations


  • Are reduced, they gain electrons at the cathode
• Anions


  • Are oxidised, they lose electrons at the anode
• Electrolysis


  The ions discharged when an aqueous solution is electrolysed using inert electrodes depend on the relative reactivity of the elements involved
• At the negative electrode


  1. Metal will be produced on the electrode if it is less reactive than hydrogen

  2. Hydrogen will be produced if the metal is more reactive than hydrogen
• Hydrogen


  • H
• Chloride


  • Cl
• Sodium chloride solution


  Sodium chloride, hydrogen + chlorine
• Uses of the products

  • Chlorine: Bleach and PVC
  • Hydrogen: Margarine
  • Sodium hydroxide: Bleach and soap
• At the positive electrode

  1. Oxygen is formed

  2. If you have a halide ion (Cl, I, Br) then you will get chlorine, bromine or iodine formed at that electrode
• Water molecules break down producing hydrogen ions and hydroxide ions that are discharged
• At the cathode (Higher)

  2H⁺ + 2e⁻ → H₂
• At the anode (Higher)

  2Cl⁻ → Cl₂ + 2e⁻
• The positive ion moves towards the negative electrode (cathode) and the negative ion moves towards the positive electrode (anode).
• Electrons flow from the negative to the positive electrode.
• Electrolysis


  The breaking down of a compound using electricity
• Electrolysis


  • Ionisation occurs during electrolysis
  • Ions in solution are free to move (electrolyte)
• Oxidation


  Loss of electrons
• Reduction


  Gain of electrons
• Oxidation-reduction at the cathode

  1. Reduction takes place

  2. Oxidation takes place
• Oxidation-reduction at the anode

  1. Oxidation takes place

  2. Reduction takes place