Identification of ions by chemical and spectroscopic means

• If a sample containing a mixture of ions is used, some flame colours can be masked (you won't be able to see them)
• Metal hydroxides


  • Aluminium, calcium and magnesium ions form a white precipitate with NaOH
  • Only aluminium's precipitate dissolves when excess NaOH is added
  • Copper(II) produces a blue precipitate
  • Iron(II) produces a green precipitate
  • Iron(III) produces a brown precipitate
• Forming metal hydroxides


  1. Cu2+ + 2OH- -> Cu(OH)2

  2. The Na from the NaOH and whatever the metal ion was bonded to will react to form a compound together: e.g. CuCl2 + 2NaOH -> Cu(OH)2 + 2NaCl
• Carbonates


  • Carbonates react with dilute acids to create carbon dioxide
  • This gas can be bubbled through limewater, if the limewater goes cloudy, the gas is CO2
• Identifying halides- (catswithbrainscanideallyyodel)


  1. First add dilute nitric acid, followed by silver nitrate solution

  2. Chloride gives a white precipitate

  3. Bromide gives a cream precipitate

  4. Iodide gives a yellow precipitate
• Identifying sulfates


  1. First add dilute hydrochloric acid, followed by barium chloride solution

  2. A white precipitate will form when sulfate ions are in this solution
• Instrumental methods


  • Elements and compounds can be detected and identified using instrumental methods
  • These are: accurate, sensitive and rapid, making them advantageous compared to chemical tests
• Flame emission spectroscopy


  • Example of an instrumental method used to analyse metal ions in solutions
  • Sample is put into a flame and the light given out is passed through a spectroscope
  • Output is a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations
• Flame tests

  • can be used to identify metal ions