Anode and cathode during electrolysis of selected aqueous solutions

Describe, using half-equations, what happens at the anode and cathode during electrolysis of selected aqueous solutions


  • Electrolysis: The passage of current through an electrolyte, causing chemical change at the electrodes.
  • In selecting the appropriate half-equations to describe the reaction occurring at each electrode in electrolytic reactions, the following guides should be considered:
    • The higher the reduction potential, the harder it is to oxidise the anion.
    • Before water molecules are oxidised to oxygen, bromine ions and iodine ions are oxidised.
    • Nitrate ions, sulfate ions and fluoride ions are never oxidised, with water being oxidised to oxygen instead.
    • The lower the electrode potential, the harder it is to reduce a metal ion.
    • Silver ions and copper ions are always reduced.
    • Potassium ions, sodium ions, calcium ions and aluminum ions are never reduced.
  • In electrolysis reactions:
    • Reduction occurs at the cathode, or negative electrode.
    • Oxidation occurs at the anode, or positive electrode.
    • The charge on the electrodes is different for an electrolytic cell and a galvanic cell:
      • The cathode is the negative in an electrolytic cell.
      • The cathode is the positive in a galvanic cell.
    • Anions carry charge towards the anode.
    • Cations carry charge towards the cathode.
    • The reactions that occur at the anode and the cathode depend on the voltage.