Testing for Halide ions

Here’s how to test for halide ions in a sample:

1. Add a few drops of dilute nitric acid (HNO3) to the sample.

  • The dilute nitric acid is added to remove any carbonate ions. Carbonate ions can also react with silver nitrate to form a white precipitate, which could be confused with the precipitate of halide ions, leading to a false positive result.

2. Add a few drops of dilute silver nitrate (AgNO3) solution.

3. Observe the colour of the precipitate that forms. The colour of the precipitate identifies the halide ion present in the sample.

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The table below shows the precipitate colour for each halide ion.

Halide ionPrecipitate colourEquation
Chloride (Cl⁻)WhiteAg⁺ (aq) + Cl⁻ (aq) → AgCl (s)
Bromide (Br⁻)CreamAg⁺ (aq) + Br⁻ (aq) → AgBr (s)
Iodide (I⁻)YellowAg⁺ (aq) + I⁻ (aq) → AgI (s)

AgCl producing a white precipitate in a test tube, AgBr with a cream precipitate in another test tube, and AgI showing a yellow precipitate in a third test tube.

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