IGCSE Chemistry: Testing for cations

Aluminium (Al3+) Test: Add aqueous sodium hydroxide.

white ppt., soluble in excess giving a colourless solution

Aluminium (Al3+) test - Effect of Aqueous Ammonia

White precipitate, insoluble in excess

ammonium (NH4+) - effect of aqueous sodium hydroxide

ammonia produced on warming

Calcium (Ca2+) - effect of aqueous sodium hydroxide

white ppt., insoluble in excess

calcium (Ca2+) - effect of aqueous ammonia

no ppt., or very slight white ppt.

chromium (III) (Cr3+) - effect of aqueous sodium hydroxide

green ppt., soluble in excess

chromium (III) (Cr3+) - effect of aqueous ammonia

grey-green ppt., insoluble in excess

copper (Cu2+) - effect of aqeuous sodium hydroxide

light blue ppt., insoluble in excess

copper (Cu2+) - effect of aqeuous ammonia

light blue ppt., soluble in excess, giving dark blue solution

iron (II) (Fe2+) - effect of aqueous sodium hydroxide

green ppt., insoluble in excess

iron (II) (Fe2+) - effect of aqueous ammonia

green ppt., insoluble in excess

iron (III) (Fe3+) - effect of aqueous sodium hydroxide

red-brown ppt., insoluble in excess

iron (III) (Fe3+) - effect of aqueous ammonia

red-brown ppt., insoluble in excess

Zinc (Zn2+) test - Effect of Aqueous Sodium Hydroxide

white ppt., soluble in excess, giving a colourless solution

Zinc (Zn2+) (aqueous ammonia)

white ppt., soluble in excess, giving a colourless solution

Lithium (Li+) flame test

red

Sodium (Na+) flame test

yellow

Potassium (K+) flame test

lilac

Copper (II), Cu2+ flame colour

blue-green