Testing for Ions

Testing for sulphate ions
1. Use barium chloride solution
  1. If added to a sample of water containing sulphate ions, barium sulphate is formed.
    1. Insoluble in water
    2. White precipitate
Testing for halide ions
1. Use silver nitrate and nitric acid
  1. Works for chloride
    1. Silver chloride will be the precipitate
      1. Precipitate will be white
  2. Works for bromide
    1. Silver bromide will be the precipitate
      1. Precipitate will be cream
  3. Works for iodide
    1. Silver iodide will be the precipitate
      1. Precipitate will be pale yellow
  4. If silver nitrate solution and nitric acid is added in drops to a solution containing halide ions the silver halide is formed
    1. Insoluble in water
      1. Precipitate
    2. Silver nitrate solution + sodium bromide solution → sodium nitrate solution + solid silver bromide
Flame tests
1. How to do a flame test
  1. 1. Dip a clean flame test loop in the sample solution
    1. 2. Hold the flame test loop at the edge of a Bunsen burner flame
      1. 3. Observe the changed colour of the flame, and decide which metal it indicates
        4. Clean the loop in acid and rinse with water, then repeat steps 1 to 3 with a new sample
2. Common flame tests
  1. Barium
    1. Pale green flame
  2. Calcium
    1. Red
  3. Copper
    1. Green/Blue
  4. Lithium
    1. Brick red flame
  5. Sodium
    1. Yellow/Orange
  6. Potassium
    1. Lilac
3. Flame tests are useful for confirming the results of a precipitate test
4. To identify an alkali metal, a flame test must be used instead of a sodium hydroxide precipitate test. This is because the alkali metals do not form precipitates with sodium hydroxide.

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Testing for Ions

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