NaOH

• Dilute sodium hydroxide solution is used in tests for some cations, which form insoluble metal hydroxides. The metal hydroxides appear as precipitates.
• Aluminium, calcium and magnesium all produce white precipitates
• However if excess sodium hydroxide is added the aluminium hydroxide will dissolve and turn colourless whereas the calcium and magnesium hydroxides would remain unchanged
• Copper (II) would form a blue precipitate
• Iron (II) would form a green precipitate
• Iron (III) would form a brown precipitate