Qualitative Analysis Flashcards
(26 cards)
What colour is a Li+ flame
Red
What colour is a Na+ flame
Yellow
What colour is a K+ flame
Lilac
What colour is a Ca2+ flame
Orange-red
What colour is a Cu2+ flame
Blue-green
What must you add to test for cations (positive ions)
Sodium hydroxide
How to test for ammonium ions
Add sodium hydroxide - if the gas produced turns moist red litmus paper blue then ammonium ions (NH4+) are present
How to test for Cu2+ (2)
- Flame test - blue-green flame
- Add sodium hydroxide and then a blue precipitate is formed
How to test for Fe2+
Add sodium hydroxide - green precipitate
How to test for Fe3+
Add sodium hydroxide - orange-brown precipitate
Why may iron(II) salts’ green precipitate turn brown after a while
It is oxidised by the air
What form must the salt be in if you are looking for a precipiate
In solution
How to test for Cl-
Add dilute nitric acid then silver nitrate solution - white precipitate
How to test for Br-
Add dilute nitric acid followed by silver nitrate solution - cream precipitate
How to test for I- (iodide)
Add dilute nitric acid followed by silver nitrate solution- yellow precipitate
How to test for carbonate ions CO3 2-
Add dilute hydrochloric acid and then test gas produced by bubbling through limewater - limewater goes cloudy
How to test for sulphate ions SO4 2-
Add dilute hydrochloric acid then aqueous barium chloride - white precipitate
Why can we not use hydrochloric acid when testing for chlorine/bromine/iodine
Because it contains chloride ions and will react with the silver nitrate to form a precipitate, therefore providing potentially misleading results
How to test for hydrogen
Squeaky pop when lit splint put close to a test tube with hydrogen in
How to test for oxygen
Relights a glowing splint
How to test for chlorine gas
It bleaches moist litmus paper blue
How to test for ammonia
Ammonia gas will turn moist red litmus paper blue
How to test for carbonate dioxide
Bubble through limewater - goes cloudy / white precipitate formed
