Chemical tests

Testing for cations

Testing for anions

Other chemical test

Hydroxide tests

What colour they turn

Fe2+ - turns green

Fe3+ - brown

Cu2+ - blue

How to perform the test

Sodium hydroxide solution is added to a solution of them metal ions

Ammoniums cations

No precipitate is formed

heat mixture, produces gas

turns damp red litmus paper blue

ammonia gas is an alkali

Hydrogen (H2)

Flammable gas with low density, very explosive

insert lit splint into tube of hydrogen gas

click to edit

Oxygen (O2)

supports combustion

insert glowing splint into tube of oxygen, should re-ignite

Carbon dioxide (CO2)

doesn't support combustion

displaces oxygen

pass carbon dioxide through limewater, if it turns cloudy white, then gas is present

Ammonia (NH3)

soluble in water

smells and is poisonous

turns litmus paper blue when pink litmus paper is inserted into gas

click to edit

Chlorine (Cl2)

pale green gas

poisonous

insert damp blue litmus paper into tube of gas, if it turns pink then bleaches, it is present

Sulfate

SO4 2-

add few drops of barium sulphate chloride solution, solution must be acidified with dilute hydrochloric acid first, white precipitate of barium sulphate will form

BaSO4

Halides

Cl-, Br-, I- ions are all halides

Precipitates

chlorine white

bromine cream

Iodine yellow

Carbonate

carbonate ions are CO3 2-

can be detected by adding an acid into the solution

carbon dioxide bobbles if carbonate ions are present

limewater used to identify and confirm presence of carbon dioxide

Flame tests

How to perform the test

Flame test wire cleaned by dipping it into hydrochloric acid and being burned for a while

wire dipped into solid sample of compound

put on edge of blue bunsen flame

flame produced indicates alkali metal ion present in the compound

Colours from results

Li+ red

Na+ yellow

K+ lilac

Ca2+ orange-red

Cu2+ blue-green