electrolysis

• Electrolysis

  The breaking down of substances through electricity
• Substances for electrolysis

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

  Mobile charged particles must be present
• Examples of 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
  • Play an important role in the electrolytic cell
  • Have free moving electrons which enables them to conduct electricity
• 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
• Components of an electrolytic cell

  1. Battery

  2. Electrode

  3. 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
  • 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 for electrolytic cell diagram

  1. Identify positive and negative terminal of power source

  2. Label direction of electron flow

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

  4. Label movements of ions in cathode and anode
• Reduction and oxidation will always occur in the cathode and anode respectively
• Positive ions

  Discharged at the cathode
• Negative ions

  Discharged at the 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
• Inert electrodes


  Electrodes that do not conduct electricity
• 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
• Inert electrodes


  • Graphite
  • Platinum
• Graphite

  • High melting point
  • 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
• Anode burn off


  When oxygen gas is produced at the anode, carbon in the graphite will react with oxygen gas to form carbon dioxide, causing the anode to decrease in size and need to be replaced regularly
• Molten binary ionic compound


  Typically a salt containing one cation and one anion in the liquid state
• Metal cathodes and anodes not made from platinum


  Generally undergoes oxidation