Qualitative analysis

• Testing for aqueous halide ions

  1. Add silver nitrate solution

  2. Add dilute, aqueous ammonia (and also concentrated ammonia)
• Chloride ions + silver nitrate


  White precipitate (silver chloride)
• Cl-(aq) + Ag+(aq)


  AgCl(s)
• Bromide ions + silver nitrate

  Cream precipitate (silver bromide)
• Ag+(aq) + Br-(aq)


  AgBr(s)
• Iodide ions + silver nitrate


  Yellow precipitate (silver iodide)
• Ag+(aq) + I-(aq)


  AgI(s)
• For ionic equations, solids cannot be split into their ions
• The same ion on either side of the arrow can be cancelled out if it has not changed charge or state (spectator ions)
• Precipitates are always shown as being in the solid state
• Testing for the ammonium ion

  1. Add sodium hydroxide to the sample

  2. Heat the solution to turn the ammonia into gas

  3. Damp red litmus paper turns blue

  4. Smell of ammonia is very distinct and noticeable
• NH4+(aq) + OH-(aq)


  NH3(aq) + H2O (l)
• Testing for the carbonate ion

  1. Add dilute hydrochloric acid

  2. Bubble the gas through lime water
• CO3^2-(aq) + 2H+(aq)


  CO2(g) + H2O(l)
• CO2(g) + Ca(OH)2(aq)


  CaCO3(s) + H2O(l)
• Testing for the sulfate ion

  Use a source of barium ions (barium nitrate or barium chloride solution)
• SO4^2-(aq) + Ba2+(aq)


  BaSO4(s)
• BaSO4 is a white precipitate as it is insoluble