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There are many anions, however, we are required to know the tests for just a few. These are:-

• Chloride, Cl^-
• Bromide, Br^-
• Iodide, I^-
• Sulfate, SO₄^2-
• Carbonate, CO₃^2-

Sulfate and carbonate ions can be classed as molecular ions.

Testing for each anion

Apparatus and chemicals

• Test tubes (x 5)
• Test-tube rack
• Small beakers (3 x 100 cm³)
• Disposable pipettes/droppers
• Sodium sulfate solution (0.2 mol/dm³)
• Sodium carbonate solution (0.2 mol/dm³)
• Sodium chloride solution (0.2 mol/dm³)
• Potassium bromide solution (0.2 mol/dm³)
• Potassium iodide solution (0.2 mol/dm³)
• *Barium chloride solution (0.2 mol/dm³)
• Silver nitrate solution (0.2 mol/dm³)
• Nitric Acid (0.2 mol/dm³)
• Limewater
• Hydrochloric acid solution (2 mol/dm³)

Safety - follow general safety advice of teacher of all solutions – taking special care with *barium chloride solution.

Note: In all the following reactions the ions are present in solutions. To test for these ions if a solid is supplied, simply dissolve 1 spatula of the solid in deionised water. The carbonate can be tested as a solid.

To test for Sulfate Ions

• Add sodium sulfate solution to the test-tube until the tube is 1/3 full.
• Add barium chloride solution drop wise.
• A white precipitate indicates a sulfate ion.

To test for Halide Ions – these are chloride, bromide or iodide ions

• Add each of the 3 solutions to separate test-tubes until the tubes are 1/3 full each.
• Add four drops of nitric acid, shake gently.
• Add silver nitrate solution drop wise
• A white precipitate indicates the presence of the chloride ion.
• A cream precipitate indicates the presence of the bromide ion.
• A yellow precipitate indicates the presence of the iodide ion.

To test for Carbonate Ions

• Take a small amount of solid or solution.
• Add a little dilute hydrochloric acid.
• Collect any gas formed, this is easily done by opening and closing an empty disposable pipette/dropper above the reaction. The dropper contents are then bubbled through 1cm³ of limewater.
• A colourless gas is given off that turns limewater cloudy/milky indicates a carbonate ion.

It is a good idea to take the time to really learn these tests, you may find it useful to make your own summary sheet of all the tests, both for cations and anions.