Qualitative analysis

• Describe the test to identify carbonate ions


  • Add dilute nitric acid to the solution
  • Effervesence / fizzing / bubbles could mean CO2
  • Test the gas with limewater -> If goes cloudy, then definetely has CO2
• Describe the test to identify sulfate ions

  • Add barium nitrate
  • If sulfate is present, a white precipitate of BaSO4 (barium sulfate) is formed
• Describe the test to identify halide ions

  • Add silver nitrate
  • If chlorine ions (Cl-) are present, a white precipitate will form
  • If bromine ions (Br-) are present, a cream precipitate will form
  • If iodide ions (I-) are present, a yellow precipitate will form
  • Then add aqueous ammonia to test the solubility of the precipitate
• Why do you need to add aqueous ammonia to identify halide ions?


  To test the solubility of the precipitates and to able to identify the different colours easier
• Do chlorine ions dissolve in dilute or concentrated NH3?

  Dilute
• Do bromine ions dissolve in dilute or concentrated NH3?


  Concentrated
• Do iodide ions dissolve in dilute of concentrated NH3?


  Neither
• Why must the carbonate test be carried out first?


  • Because barium carbonate is insoluble
  • This means that barium nitrate would give a white precipitate with carbonates as well as with sulfates, so carbonate must be eliminated first
  • Neither sulfate nor halide ions produce bubbles with dilute acid
  • The carbonate test can be carried out without the possibility of an incorrect conclusion
  • If the test produces no bubbles, then no carbonate is present and you can proceed to the next test
• Why must the sulfate test be carried out before the halide test?

  • Because silver sulfate is insoluble
  • This means that silver nitrate would give a white precipitate with sulfates as well as with halides, so the sulfate must be eliminated first
• Describe the test for ammonium ions $NH_4^+$


  • Add sodium hydroxide
  • Ammonia will be produced
  • Warm the solution to release NH3+ gas
  • The gas will turn damp red litmus paper to blue
• Ionic equation for testing for carbonate ions

  Ca(OH)2 (aq)+ CO2 (g) -> CaCO3 (s) + H2O (L)
• Ionic equation for testing sulfate ions

  Ba+ (aq) + SO4 2- -> BaSO4 (s)
• Ionic equation for testing halide ions e.g. Br

  Ag+ (aq) + Br- (aq) -> AgBr (s)
• Ionic equation for testing ammonium ions

  NH4+ (aq) + OH- (aq) -> NH3+ (aq) + H2O (L)