Section 1 of 5Silver Nitrate Test
1
Dissolve the sample in water and add dilute nitric acid to remove carbonate ions that would also give a precipitate.
2
Add silver nitrate solution drop by drop.
3
A precipitate of the silver halide forms: Ag⁺(aq) + X⁻(aq) → AgX(s).
4
Observe the colour of the precipitate to identify the halide present.
5
Add ammonia solution to confirm the identity of any precipitate you cannot decide by colour alone.
Section 2 of 5Results
Chloride
- AgCl is white and dissolves in dilute ammonia solution to give a colourless solution.
Bromide
- AgBr is cream and dissolves only in concentrated ammonia solution.
Iodide
- AgI is yellow and does not dissolve in concentrated ammonia solution.
Fluoride
- Silver fluoride is soluble, so no precipitate forms with fluoride ions.
| Halide | Colour with AgNO₃ | Dilute NH₃ | Conc. NH₃ |
|---|---|---|---|
| Cl⁻ | White | Dissolves | Dissolves |
| Br⁻ | Cream | Insoluble | Dissolves |
| I⁻ | Yellow | Insoluble | Insoluble |
Section 3 of 5Why Ammonia Dissolves the Precipitate
Why Ammonia Dissolves the Precipitate
Complex ion
- Ammonia replaces chloride to form the soluble diamminesilver(I) ion: AgCl(s) + 2NH₃(aq) → [Ag(NH₃)₂]⁺(aq) + Cl⁻(aq).
Solubility product
- Silver iodide is less soluble than silver chloride,
- so it needs a higher ammonia concentration,
- and iodide never dissolves enough to be seen.
Colour
- The solution formed is colourless, since the silver(I) ion has a full d sub-shell.
Section 4 of 5Practical Care
Practical Care
Acid choice
- Use nitric acid only;
- hydrochloric acid would add chloride and sulfuric acid would form insoluble silver sulfate.
Order
- Always acidify first, then add silver nitrate, as carbonate or hydroxide would give false results.
Light
- Silver halides darken in light as silver is formed, so observations should be made promptly.
Section 5 of 5Exam Checklist & Tips
2.3.3 – Key Points for the Exam
- Precipitate An insoluble solid formed when two solutions react.
- Halide ion A negative ion of a Group 17 element, such as Cl⁻, Br⁻ or I⁻.
- Complex ion A central metal ion surrounded by ligands bonded by coordinate bonds.
- Ligand A molecule or ion that donates a pair of electrons to a metal ion.
Common Mistakes
- Acidifying with hydrochloric or sulfuric acid.
- Reporting the bromide precipitate as white rather than cream.
- Saying silver iodide dissolves in concentrated ammonia.
- Forgetting to add the nitric acid, so carbonate gives a false positive.