Testing for ions Flashcards
Flame tests
Sodium - yellow
Potassium - lilac
Barium - green
Calcium - brick red
Copper - blue green
Lithium - crimson
Heat energy excites electrons so they emit light when they fall
Testing for halides with silver nitrate solution (AgNO3)
Chloride - white
Bromide - cream
Iodide - yellow
Testing for sulfates
Add dilute HCl
Add barium chloride solution
White precipitate of barium sulfate will form
The HCl gets ride of carbonate ions which would otherwise produce a precipitate
Using litmus paper to test for hydroxides
Same as testing for an alkaline solution
Red litmus paper will turn blue
Using litmus paper to test for ammonium compounds
Ammonia gas is alkaline so will turn red litmus paper blue
Litmus paper must be damp so ammonia gas can dissolve
Add NaOH and gently heat. Ammonia gas will be given off
Using HCl to test for carbonates
Carbonates will fizz as they give off carbon dioxide
Test for carbon dioxide with limewater
Limewater turns cloudy
Bubble gas through test tube
NaOH (or other hydroxide solutions) to test for metal ions
Silver - brown ppt
Calcium - white
Copper (II) - blue
Lead (II) - white
Iron (II) green
Iron (III) - red brown
Zinc - white initially then redissolves in excess Naoh to form colourless solution
Aluminium same as zinc
Testing for nitrates
Warm solution with NaOH and aluminium foil
The aluminium reduces the nitrate ions to ammonium ions
The ammonium ions react with the hydroxide ions to produce ammonia gas and water
Damp red litmus paper turns blue
False positives…
If testing for sulfate ions ensure there are no carbonate ions
If testing for a halide ion ensure there are no sulfate ions
Add a dilute acid to test solutions, this will get rid of an anions you don’t want
The acid mustn’t interfere with the test though, e.g. don’t use HCl if testing for chloride ions
How remove acidic impurities
Shake with sodium hydrogen carbonate solution
