C3.4

• Cathode


  Metals (or hydrogen) are formed here in electrolysis using inert electrodes
• Anode


  Non-metals are formed here in electrolysis using inert electrodes
• Movement of ions in the electrolyte

  1. Positive ions (cations) move to negative electrode to receive electrons and are reduced

  2. Negative ions (anions) move to positive electrode to lose electrons and are oxidised
• Molten ionic compounds


  Much simpler to predict the products of electrolysis as there are no ions present except those in the ionic compound
• Predicting products of electrolysis of molten ionic compounds

  1. Identify which ions are present

  2. The + ions will go to the cathode

  3. The - ions will go to the anode
• Electrolysis of aqueous solutions of ionic compounds

  1. Hydrogen (from H+ in water) is produced at cathode unless the + ions in the ionic compound are from a metal less reactive than hydrogen

  2. Oxygen (from OH- in water) is produced at anode unless the ionic compound contains halide ions
• Electrolysis of sodium chloride solution

  • H+ ions go to cathode, H2 (g) is produced
  • Cl- ions go to anode, Cl2 (g) is produced
• Electrolysis of copper sulfate solution

  • Cu2+ ions go to cathode, Cu (s) is produced
  • OH- ions go to anode, O2 (g) is produced
• Oxidation


  Loss of electrons
• Reduction


  Gain of electrons
• Anode


  Loss of electrons, oxidation (positive electrode), anions come to it
• Cathode


  Gain of electrons, reduction (negative electrode), cations come to it
• Inert electrodes


  • Used if the products made are reactive, otherwise reactions would take place between the electrodes and the solution
• Non-inert electrodes


  • Sometimes used e.g. in purification of copper, a pure and impure copper electrode is used