AQA A-Level Chemistry Chemical Tests
QUESTIONS AND ANSWERS 2025/2026
test for Carbon Dioxide (CO2 )
turns limewater milky (sparingly soluble Ca(OH) 2 forms insoluble CaCO3 )
Chlorine (Cl2 ) test
bleaches damp litmus paper (Cl2 reacts with water to form HCl and HOCl)
Hydrogen (H2 ) test
pops with a lighted splint
Oxygen (O2 ) test
relights a glowing splint
Carbonate (CO 3 2- ) test
add dilute acid; effervescence, carbon dioxide produced
Sulfate (SO4 2- ) test
add dilute nitric acid then aqueous barium nitrate. Gives white precipitate
Chloride (Cl - ) test
add dilute nitric acid then aqueous silver nitrate. Gives white precipitate. Dissolves in dilute ammonia to
give colourless solution (of [Ag(NH 3 ) 2 ] + )
Bromide (Br - ) test
add dilute nitric acid then aqueous silver nitrate. Gives cream precipitate. Dissolves in concentrated
ammonia but not in dilute ammonia
Iodide (I - ) test
add dilute nitric acid then aqueous silver nitrate. Gives yellow precipitate. Does not dissolve in either
concentrated or dilute ammonia
Iron II (Fe 2+ ) test
add aqueous sodium hydroxide gives green precipitate, insoluble in excess
Iron III (Fe 3+ ) test
add aqueous sodium hydroxide gives orange/brown precipitate, insoluble in excess
Copper (Cu 2+ ) test
add aqueous sodium hydroxide gives blue precipitate, insoluble in excess. Or add ammonia: gives a blue
precipitate which dissolves in excess to give a blue solution
Calcium (Ca 2+ ) test
QUESTIONS AND ANSWERS 2025/2026
test for Carbon Dioxide (CO2 )
turns limewater milky (sparingly soluble Ca(OH) 2 forms insoluble CaCO3 )
Chlorine (Cl2 ) test
bleaches damp litmus paper (Cl2 reacts with water to form HCl and HOCl)
Hydrogen (H2 ) test
pops with a lighted splint
Oxygen (O2 ) test
relights a glowing splint
Carbonate (CO 3 2- ) test
add dilute acid; effervescence, carbon dioxide produced
Sulfate (SO4 2- ) test
add dilute nitric acid then aqueous barium nitrate. Gives white precipitate
Chloride (Cl - ) test
add dilute nitric acid then aqueous silver nitrate. Gives white precipitate. Dissolves in dilute ammonia to
give colourless solution (of [Ag(NH 3 ) 2 ] + )
Bromide (Br - ) test
add dilute nitric acid then aqueous silver nitrate. Gives cream precipitate. Dissolves in concentrated
ammonia but not in dilute ammonia
Iodide (I - ) test
add dilute nitric acid then aqueous silver nitrate. Gives yellow precipitate. Does not dissolve in either
concentrated or dilute ammonia
Iron II (Fe 2+ ) test
add aqueous sodium hydroxide gives green precipitate, insoluble in excess
Iron III (Fe 3+ ) test
add aqueous sodium hydroxide gives orange/brown precipitate, insoluble in excess
Copper (Cu 2+ ) test
add aqueous sodium hydroxide gives blue precipitate, insoluble in excess. Or add ammonia: gives a blue
precipitate which dissolves in excess to give a blue solution
Calcium (Ca 2+ ) test
