Ion Testing

• • If the sample to be tested is a solid, then it must be dissolved in deionised water and made into an aqueous solution
• Group 2 Metal ions

  • 0.1 mol dm-3 group 2 chloride solution/ sample added
  • Dilute sodium hydroxide solution (NaOH) added
  • Mix
  • Continue to add sodium hydroxide until it is in excess
• Group 2 testing with ammonium solution: Mg2+ white precipitate, Ca2+, Sr2+, Ba2+ no change
• Group 2 testing with excess sodium hydroxide: Mg2+, Ca2+ white precipitate. Sr2+ slight white precipitate. Ba2+ no change
• Group 2 testing with excess sulfuric acid: Mg2+ colourless solution. Ca2+ slight white precipitate. Sr2+, Ba2+ white precipitate.
• Ammonium Ions:

  • Sodium hydroxide added using pipette
  • heat gently in water bath, produces ammonia gas
  • A pair of tongs used to hold damp red litmus paper above test tube
  • red litmus paper will become blue in the presence of ammonia gas
• Halide ions:

  Add nitric acid to sample

  Add silver nitrate
• Halide ion precipitates:

  white precipitate= Silver chloride

  cream precipitate= silver bromide

  yellow precipitate= silver iodide
• Halide tests using ammonia solution:

  AgCl= soluble in dilute ammonia

  AgBr= soluble in concentrated ammonia

  AgI= insoluble in concentrated ammonia
• Hydroxide Ions:

  • Test the pH of the solution using red litmus paper or universal indicator paper
  • The presence of hydroxide ions will turn red litmus paper blue and the pH will be clearly alkaline on the universal indicator paper
• Carbonate Ions:

  • dilute hydrochloric acid should be added to a test tube using a pipette
  • An equal amount of sodium carbonate solution should then be added using a clean pipette
  • As soon as the sodium carbonate solution is added, a bung with a delivery tube should be attached
  • other test tube contains limewater
  • Carbonate ions will react with hydrogen ions from the acid to produce carbon dioxide gas
  • Carbon dioxide gas will turn the limewater milky
• Sulfate Ions:

  • Acidify the sample with dilute hydrochloric acid and then add a few drops of aqueous barium chloride
  • If a sulfate is present then white precipitate of barium sulfate is formed