Identification of Ions and Gases

Copper (II), Cu^2+, can be identified by a blue precipitate formed after reacting aqueously with sodium hydroxide.
Iron (II), Fe^2+, produces a green precipitate with sodium hydroxide, which then turns brown.
Iron (III), Fe^3+, when reacted with sodium hydroxide, forms a reddish-brown precipitate.
Calcium, Ca^2+, forms a white precipitate with sodium hydroxide, insoluble in excess.
Aluminium, Al^3+, reacts with sodium hydroxide to produce a white precipitate, dissolved in excess.
Ammonium, NH4+, is tested by warming with sodium hydroxide, which gives off ammonia gas that turns damp red litmus paper blue.

Chloride, Cl^–, when treated with dilute nitric acid and silver nitrate, forms a white precipitate.
Bromides, Br^– and Iodides, I^–, when reacted with dilute nitric acid and silver nitrate form a cream or yellow precipitate respectively.
Sulphates, SO4^2–, when reacted with dilute hydrochloric acid and barium chloride, form a white precipitate.
Carbonates, CO3^2–, on reacting with any dilute acid, produce carbon dioxide, detected by bubbling through lime water (turning from clear to milky).

Hydrogen gas is recognised by a ‘pop’ sound when a lit splint is introduced in its test tube.
Oxygen gas relights a glowing splint.
Carbon dioxide, when bubbled through clear lime water, turns it milky.
Ammonia gas is alkaline and has a pungent odour. It turns damp red litmus paper blue.
Chlorine gas has a sharp, bad smell and bleaches damp litmus paper.