Cation Tests Aqueous

Copper (II) (Cu²⁺)

• +NH₃ - Blue precipitate (soluble in excess NH₃, forming a deep blue solution)

• +NaOH - Light blue precipitate (insoluble in excess NaOH)

Iron (II) (Fe²⁺)

• +NH₃ - Green precipitate (insoluble in excess NH₃, oxidises to turn brown in air)

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

Iron (III) (Fe³⁺)

• +NH₃ - Brown precipitate (insoluble in excess NH₃)

• +NaOH - Brown precipitate (insoluble in excess NH₃)

Aluminium (Al³⁺)

• +NH₃ - White precipitate (insoluble in excess NH₃)

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

Zinc (Zn²⁺)

• +NH₃ - White precipitate (soluble in excess NH₃, forming a colourless solution)

• +NaOH - White precipitate (soluble in excess NH₃, forming a colourless solution)

Calcium (Ca²⁺)

• +NH₃ - No precipitate or very slight white precipitate in NH₃

• +NaOH - White precipitate (insoluble in excess NaOH)

Chromium (III) (Cr³⁺)

• +NH₃ - Grey-green precipitate (partially dissolves in excess NH₃, forming a violet solution)

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

Ammonium (NH₄⁺)

• +NH₃ - No reaction with aqueous ammonia

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