Tests for Aqueous Cations

Aluminium ion

aq sodium hydroxide: white ppt. soluble in excess, dissolves to give colourless solution
aq ammonia: white ppt. insoluble in excess

Ammonium ion (NH4+)

aq sodium hydroxide: ammonia produced on warming , test for ammonia = damp red litmus blue
aq ammonia: n/a

Calcium ion

aq sodium hydroxide: white ppt. insoluble in excess
aq ammonia: no ppt. or very slight white ppt.

Chromium (III) ion

aq sodium hydroxide: green ppt. soluble in excess, dissolves to form green solution
aq ammonia: green ppt. insoluble in excess

Copper (II) ion

aq sodium hydroxide: light blue ppt. insoluble in excess
aq ammonia: light blue ppt. soluble in excess, dissolving to give dark blue solution

Iron (II) ion

aq sodium hydroxide: green ppt. insoluble in excess, turns brown near surface on standing

aq ammonia: green ppt. insoluble in excess, turns brown near surface on standing

Iron (III) ion

aq sodium hydroxide: red-brown ppt. insoluble in excess
aq ammonia: red-brown ppt. insoluble in excess

Zinc ion

aq sodium hydroxide: white ppt. soluble in excess, dissolves to give colourless solution
aq ammonia: white ppt. soluble in excess, dissolves to give colourless solution