Halide Ions (Oxford AQA IGCSE Chemistry)
Revision Note
Author
Alexandra BrennanExpertise
Chemistry
Test for Halide Ions
Negatively charged non-metal ions are known as anions
You must be able to test for halide ions
These are the ions formed by the elements in Group 7
How to test for halide ions
Add silver nitrate solution, AgNO3, in the presence of nitric acid
If a halide is present it forms a silver halide precipitate
For example, the following reaction occurs between aqueous potassium chloride and silver nitrate solution:
potassium chloride + silver nitrate → potassium nitrate + silver chloride
KCl (aq) + AgNO3 (aq) → KNO3 (aq) + AgCl (s)
In this case, the silver halide formed is silver chloride, which forms a precipitate
This is represented using the state symbol, (s)
Depending on the halide present, a different coloured precipitate is formed, allowing for the identification of the halide ion
Silver chloride forms a white precipitate
Silver bromide forms a cream precipitate
Silver iodide forms a yellow precipitate
Testing for halide ions
Exam Tip
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.
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