- Acidify the sample with dilute nitric acid (HNO3) followed by the addition of silver nitrate solution, AgNO3
- The acidification is done to remove carbonate ions that might give a false positive result
- If a halide is present it forms a silver halide precipitate:
Ag+(aq) + X–(aq) → AgX(s)
- Depending on the halide present, a different coloured precipitate is formed, allowing for identification of the halide ion
- Silver chloride is white, silver bromide is cream and silver iodide is yellow
Each silver halide produces a precipitate of a different colour
The acidification step in the halide ion test must be done with nitric acid rather than hydrochloric acid, as HCl contains chloride ions which would interfere with the results.