4) Electrolysis of aqueous solutions

• When ionic compounds are dissolved in water to form aqueous solutions, it is slightly harder to predict the products of electrolysis.
• The water molecules break down to form hydroxide ions, OH, and hydrogen ions, H+
• At the negative electrode:

  • Hydrogen is produced if the metal is more reactive than hydrogen.
  • The metal is produced if the metal is less reactive than hydrogen.
• At the positive electrode:

  • Oxygen is produced unless the solution contains halide ions.
  • If halide ions are present, then the halogen is produced.
• In the electrolysis of sodium chloride solution:

  • Hydrogen is released at the negative electrode.
  • Chlorine gas is released at the positive electrode.
• When electrolysis is used to extract metal, the positive electrode is made of carbon.