AS-Level Group 7 (Halogens)

  • Silver nitrate (AgNO ) can be used to identify halide ions in a solution.

    • Silver ions combine with halide ions to produce silver halide precipitates with different colours.

      • Fluoride ions do not produce a precipitate.

      • Chloride ions produce a white precipitate.

      • ​Bromide ions produce a cream precipitate.

      • ​Iodide ions produce a yellow precipitate.

    • The precipitates have different solubilities in ammonia (NH ), which can be used to help further identify the halides.

      • AgCl(s) dissolves in dilute ammonia.

      • AgBr(s) dissolves in concentrated ammonia only.

      • AgI(s) does not dissolve in concentrated ammonia.

  • Dilute nitric acid is added before silver nitrate to remove impurities that may also form precipitates with the silver ions.




Halide Ion Tests (Identifying Halide Ions)


Halide ions can be identified in solution based upon the products formed when they react with silver ions.


The test


Silver nitrate (AgNO ) is added to a solution with halide ions and dilute nitric acid.


Dilute nitric acid is added prior to the silver nitrate to react with any impurities (mainly carbonate ions) that may be present in the solution. Carbonate ions, for example, would form a white precipitate with the silver ions, making the identification of silver halide salts difficult.

The halides (with the exception of fluoride) produce precipitates that are different colours and, more importantly, have different solubilities in ammonia (NH ).