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