5.1

• Flame test for cations

  1. Take a solution of the ion, ideally in concentrated HCL

  2. Clean a nichrome wire by dipping into concentrated HCL and heating in a Bunsen flame

  3. Dip the cleaned wire in the solution to be tested and heat in a hot Bunsen flame
• Flame test colours


  • Barium (Ba2+): apple green
  • Calcium (Ca2+): red
  • Copper (Cu2+): blue
  • Lithium (Li+): carmine red
  • Potassium (K+): lilac
  • Sodium (Na+): yellow
• Chemical tests for cations

  1. Add dilute sodium hydroxide

  2. Observe behaviour with excess sodium hydroxide or aqueous ammonia solution
• Behaviour of metal ions with NaOH, excess NaOH or aqueous ammonia

  • Aluminium (Al): White precipitate, precipitate redissolves
  • Copper (Cu): Blue/turquoise precipitate, precipitate does not redissolve
  • Iron (Fe): Dark green precipitate that darkens in air, precipitate does not redissolve
  • Iron (Fe3+): Brown precipitate, precipitate does not redissolve
  • Lead (Pb): White precipitate, precipitate redissolves
• Aluminium and lead cannot be distinguished using NaOH, but addition of potassium iodide solution gives a yellow precipitate of lead(II) iodide if Pb2+ ions are present
• Chemical tests for carbonates

  1. Heat a solid carbonate strongly to decompose it and release CO2, which can be identified by bubbling through limewater

  2. Add acid to a solid or solution to produce effervescence as CO2 is released, which can be confirmed by bubbling through limewater
• Chemical tests for halides

  1. Add dilute nitric acid to the sample followed by silver nitrate solution - a precipitate indicates the presence of a halide

  2. If the precipitate does not redissolve in dilute ammonia, add concentrated ammonia
• Silver nitrate test for halide ions

  • Chloride (Cl-): White precipitate, precipitate redissolves in concentrated ammonia
  • Bromide (Br-): Cream precipitate, precipitate does not redissolve in concentrated ammonia
  • Iodide (I-): Yellow precipitate, precipitate does not redissolve in concentrated ammonia
• Chemical test for sulfates

  Add dilute hydrochloric acid followed by a few drops of barium chloride or barium nitrate solution - a dense white precipitate of barium sulfate indicates the presence of sulfate ions
• Silver carbonate, silver sulfate and barium carbonate are all insoluble
• Carbonates react with acid to form carbon dioxide and water