Qualitative Analysis

Question 1

How do you test for carbonate ions?

Answer 1

Add equal vol dilute nitric acid to carbonate solution.
If substance is carbonate will see fizzing as CO2 gas produced.
Prove gas CO2 bubble through limewater and limewater (Ca(OH)2) will turn cloudy as a calcium carbonate precipitate forms.

Question 2

How do you test for sulphate ions?

Answer 2

Add equal vol aqueous barium nitrate to a solution.
If present will see white precipitate.

Question 3

How do you test for halide ions?

Answer 3

Add equal vol of aqueous silver nitrate (aq silver ions) to aqueous halide ion.
Cl- - white precipitate that dissolves in dilute NH3
Br- - cream precipitate that dissolves in concentrated NH3
I- - yellow precipitate that won’t dissolve

Question 4

What is the sequence in which you should test?

Answer 4

1) carbonate ion
2) sulphate ion
3) halide ion
4) ammonia/ammonium ion

Question 5

Why is a carbonate test done before sulphate?

Answer 5

If carbonate ions present they will react with barium ions to produce white precipitate, giving a false positive and lead to believe sulphate ions are present.

Question 6

Why is sulphate tested before halide ions?

Answer 6

If sulphate ions present and we add silver nitrate we would see a white precipitate form who can is Ag2SO4 leading to a false positive

Question 7

How do we test for ammonium ions?

Answer 7

Heat together equal volumes of aqueous sodium hydroxide and a solution of ammonium ions.
Ammonia gas is produced
Mixture warmed and ammonia gas released
Use moist red litmus paper held in stream of gas and will turn blue if ammonia gas is present