2g) Chemical Tests Flashcards
Method for Cation flame test
1) sterilise a nichrome wire using concentrated acid / alcohol
2) Dip it into the compound to be tested to pick up a small amount of solid
3) Put the wire into a roaring blue Bunsen flame & record the colour
Colour for K+ (flame test)
Lilac
Colour for Na+ (flame test)
Yellow
Colour for Li+ (flame test)
Red
Colour for Ca ^2+ (flame test)
Orange-red
Colour for Cu ^2+ (flame test)
Blue-green
Test & result for ammonium ion (NH4 ^+)
Test: add sodium hydroxide (NaOH) to the solution/solid to be tested. Then test the gas given off with damp red litmus paper.
Result: damp red litmus turns blue
Anion test for sulphate (SO4 ^2-) & result
- Add dilute hydrochloric acid to the solution to be tested (removes other anions)
- Add an equal volume of barium chloride solution (BaCl2)
White precipitate is produced (BaSO4)
Anion test for Carbonate (CO3 ^2-) & result
- add dilute acid to the sample to be tested & look for fizzing
- test the gas evolved by bubbling it through limewater
Carbonate ion is present if limewater goes cloudy
Anion test for chloride, Bromide and iodide ions
- add dilute nitric acid (HNO3) to the sample to be tested (removes other anions)
- add silver solution (AgNO3)
Forms a precipitate
Colour for chloride ion precipitate
White
Colour for bromide ion precipitate
Cream
Colour for iodide ion precipitate
Yellow
Cation test for copper and iron (II & III) ions. (Precipitation reaction)
Add a solution of the salt to be tested to the same volume of sodium hydroxide (NaOH)
Record observations
Cu ^2+ precipitate colour
Blue
Fe ^2+ precipitate colour
Green
Fe ^3+ precipitate colour
Orange-brown
Gas test for Hydrogen
Put a lit splint into sample
Gives a ‘squeaky pop’
Gas test for Oxygen
Put a glowing splint into the sample
It re-lights
Gas test for Carbon dioxide
Bubble gas through limewater
Limewater goes clowdy
Gas test for chlorine (Cl2)
Put some damp litmus paper over the mouth of the gas jar
If chlorine present, it will be bleached
(If blue litmus paper used , it will go red first)
Gas test for ammonia (NH3)
Damp red litmus paper over the mouth of test tube / gas jar
Red litmus paper turns blue (NH3 is an alkaline gas)
Chemical test for water
Add anhydrous copper(II) sulphate (CuSO4)
It turns from white to blue
CuSO4 (white) + 5 H2O —> CuSO4 • 5H2O (blue)
