Electrolysis

• Electrolysis


  The process of breaking down an ionic compound using electrical energy
• Electrolyte


  Liquid which is broken down by an electrical charge
• Electrode


  Graphite rods which carry a current in and out of the electrolyte
• Cathode


  Negative electrode
• Anode


  Positive electrode
• Electrolysis of water


  1. Hydrogen gas is collected on the cathode

  2. Oxygen gas is collected on the anode
• Electrolysis of water (cathode)

  2H+ + 2é → H2
• Electrolysis of water (anode)

  2OH– → O2 + 2H+ + 4é
• The volume of the hydrogen formed is twice the volume of the oxygen formed, as there are two hydrogen atoms for every oxygen atom in a molecule of water (H2O)
• Electrolysis of aqueous solutions

  1. Metals lower in the reactivity series than hydrogen are formed on the cathode

  2. In the case of copper(II) chloride solution, the products are copper metal and chlorine gas
• Electrolysis of aqueous solutions (cathode)

  Cu2+ + 2é → Cu
• Electrolysis of aqueous solutions (anode)

  2Cl– → Cl2 + 2é
• Electrolysis of aqueous solutions (metals higher than hydrogen)

  2H+ + 2é → H2
• Aluminium Electrolysis


  1. aluminium oxide → aluminium + oxygen

  2. Al3+ + 3é → Al

  3. 2O2– – 4é → O2
• Alumina (aluminium oxide) dissolves in molten cryolite at a temperature much lower than its melting point, therefore saving energy
• The oxygen formed reacts with the carbon anodes, forming carbon dioxide gas and requiring anodes to be replaced frequently
• Factors impacting location of aluminium plants

  • Location near the coast to import raw materials
  • Site away from built up areas
  • Town/city within commuting distance for workforce
  • Good transport links to transport product
  • Direct electricity supply
• Properties of metals


  • Iron (steel): Strong and hard

  Aluminium: Strong, low density, good conductor of heat and electricity, resistant to corrosion

  Copper: Very good conductor of heat and electricity, malleable and ductile, attractive colour and lustre

  Titanium: Hard, strong, low density, resistant to corrosion, high melting point
• OIL


  Oxidation Is Loss (of electrons)
• RIG


  Reduction Is Gain