Cation tests (aqueous sodium hydroxide)

Copper (II) (Cu²⁺)

Light blue precipitate (insoluble in excess NaOH)

Iron (II) (Fe²⁺)

Green precipitate (insoluble in excess NaOH, oxidises to turn brown in 5 minutes in air)

Iron (III) (Fe³⁺)

Brown precipitate (insoluble in excess NaOH)

Aluminium (Al³⁺)

White precipitate (soluble in excess NaOH, forming a colourless solution)

Zinc (Zn²⁺)

White precipitate (soluble in excess NaOH, forming a colorless solution)

Calcium (Ca²⁺)

White precipitate (insoluble in excess NaOH)

Ammonium (NH₄⁺)

No precipitate, but ammonia gas is released on heating (turns damp red litmus paper blue)

Chromium (III) (Cr³⁺)

Green precipitate (soluble in excess NaOH, forming a dark green solution)