qualitative analysis

• Testing for Negative ions (anions)

  1. Add any dilute acid and observe effervescence

  2. Bubble gas through limewater to test for CO2 – will turn limewater cloudy
• Carbonate


  Fizzing due to CO2 would be observed if a carbonate was present
• Testing for presence of a sulfate

  1. Acidified BaCl2 solution is used as a reagent

  2. If barium chloride is added to a solution that contains sulfate ions a white precipitate forms
• Sulfuric acid cannot be used to acidify the mixture because it contains sulfate ions which would form a precipitate
• Testing for halide ions with silver nitrate

  1. The test solution is made acidic with nitric acid

  2. Silver nitrate solution is added dropwise
• Fluorides


  Produce no precipitate
• Chlorides


  Produce a white precipitate
• Bromides


  Produce a cream precipitate
• Iodides


  Produce a pale yellow precipitate
• Treating silver halide precipitates with ammonia solution


  1. Silver chloride dissolves in dilute ammonia to form a colourless complex ion

  2. Silver bromide dissolves in concentrated ammonia to form a colourless complex ion

  3. Silver iodide does not react with ammonia
• Hydrochloric acid cannot be used to acidify the mixture because it contains chloride ions which would form a precipitate
• The sequence of tests required is carbonate, sulfate then halide
• Testing for positive ions (cations)


  Test for ammonium ion NH4+ by the reaction with warm NaOH(aq), forming NH3 gas
• Ammonia gas


  Can be identified by its pungent smell or by turning red litmus paper blue