electrolysis

• Electrolysis


  The breaking down of substances through electricity
• Substances required for electrolysis

  • Molten or aqueous ionic compound or metals
  • Must have good electricity conductivity
• Electricity conductivity


  Requires mobile charged particles
• Mobile charged particles

  • Electrons
  • Positive and negative ions
• Mobile positive and negative ions


  Present in ionic compounds in aqueous and molten state
• Metals


  • Cannot be broken down as it is a pure element
  • Will not be involved in the process of electrolysis
  • Have free moving electrons which enables them to conduct electricity
• Alternative to inert metal electrode

  • Graphite
• Electrolysis


  Passing through of electric current through a compound to chemically separate its components
• Electrolytic cell


  A device that converts electrical energy to chemical energy
• Electrolytic cell


  • Made of battery, electrode and electrolyte
  • Negative terminal of power source connected to negative electrode (cathode)
  • Positive terminal of power source connected to positive electrode (anode)
  • Electrodes contain delocalized electrons to conduct electricity
  • Electrodes set up to ensure a close circuit
• Electrolyte


  • Electrically conductive substance in molten or aqueous state
  • Contains mobile ions that act as mobile charge carriers and conduct electricity
• Electrolytic cell

  Converts electrical energy to chemical energy as redox reactions take place in the electrodes
• Anode


  • Positively charged electrode
  • Anions are attracted to it
  • Anions lose electrons to it
  • Oxidation occurs at it
• Cathode

  • Negatively charged electrode
  • Cations are attracted to it
  • Cations gain electrons from it
  • Reduction occurs at it
• Steps to follow for an electrolytic cell diagram

  1. Identify positive and negative terminal of power source

  2. Label direction of electron flow

  3. Label cathode and anode and identify positive and negative ions of electrolyte

  4. Label movements of ions in cathode and anode
• Reduction and oxidation


  Always occur in cathode and anode respectively
• Positive ions


  Discharged at cathode
• Negative ions


  Discharged at anode
• Ionic compounds in solid state

  Unable to conduct electricity as ions are held in fixed positions in giant lattice structure and unable to move and carry electric current
• Ionic compounds in molten and aqueous state


  Able to conduct electricity as ions are able to move and carry electric current
• Substances such as distilled water, sugar, sulfur and organic compounds do not conduct electricity under any circumstances
• Metals and graphite


  Conduct electricity through the movement of delocalized electrons found in their structures
• Metal cathodes and anodes made from platinum


  • Generally do not undergo chemical changes in electrolysis
• Electrolysis of molten binary ionic compounds

  Usually carried out to decompose the compounds
• Contamination of products may occur if the electrodes take part in the process
• Inert electrodes


  • Made up of materials that are usually unreactive
  • Graphite and platinum are two substances commonly used
• Graphite


  • Has high melting point hence it will not melt when used in the electrolysis of molten binary ionic compound at high temperature
  • Will react with oxygen gas under high temperatures, forming carbon dioxide
  • Graphite anodes might need to be replaced periodically to ensure a closed circuit
• Platinum

  • Does not take part in the electrolysis process
  • Has a lower melting point than graphite hence it might melt when used in the electrolysis of molten binary ionic compounds
• Molten binary ionic compound is typically a salt containing one cation and one anion in the liquid state
• inert electrodes are electrodes that do not take part in the electrolysis process
• metal anodes made from metals other than platinum generally undergoes oxidation due to its reactivity