IGCSE CIE Chemistry: Anion and Cation Tests:

Copper (II) Cu²⁺

Aqueous Sodium Hydroxide:
Light blue precipitate
Insoluble in excess

Aqueous Ammonia:
Light blue precipitate
Soluble in excess (dark blue solution)

Iron (II) Fe²⁺

Aqueous Sodium Hydroxide:
Grey-green precipitate
Insoluble in excess

Aqueous Ammonia:
Grey-green precipitate
Insoluble in excess

Iron (III) Fe³⁺

Aqueous Sodium Hydroxide:
Reddish-brown precipitate
Insoluble in excess

Aqueous Ammonia:
Reddish-brown precipitate
Insoluble in excess

Aluminium Al³⁺

Aqueous Sodium Hydroxide:
White precipitate
Soluble in excess (colourless solution)

Aqueous Ammonia:
White precipitate
Insoluble in excess

Zinc Zn²⁺

Aqueous Sodium Hydroxide:
White precipitate
Soluble in excess (colourless solution)

Aqueous Ammonia:
White precipitate
Soluble in excess (colourless solution)

Calcium Ca²⁺

Aqueous Sodium Hydroxide:
White precipitate
Insoluble in excess

Aqueous Ammonia:
No precipitate or very slight white precipitate

Halide Ions: (Cl⁻, Br⁻, I⁻)

To a small volume of the halide solution in a test tube:

Add an equal volume of dilute nitric acid,
Add a few drops of aqueous silver nitrate,
Observe the colour of the precipitate.

Chloride: White precipitate
Bromide: Cream precipitate
Iodide: Pale yellow precipitate

Sulfate Ion: SO₄²⁻

Barium chloride or barium nitrate solution is used to test for sulfates:

Put an aqueous solution of the unknown compound into a test tube,
Add an equal volume of dilute Hydrochloric Acid,
If a white precipitate is formed the compound is a sulfate.

Nitrate Ion: NO₃⁻

This makes use of the test for ammonia:

Put an aqueous solution of the unknown compound into a test tube,
Add aqueous sodium hydroxide, then aluminium foil and warm gently,
Test the gas given off with a piece of damp red litmus paper placed at the mouth of the test tube.
If ammonia is given off, the litmus paper will turn blue - the compound is likely to be a nitrate.

Carbonate Ion: CO₃²⁻

Add dilute acid to the unknown compound (can be either solid or solution),
If a carbonate is present, effervescence will be seen.
Then test if this gas given off is carbon dioxide, using limewater.