8.3 Qualitative analysis

8.3 Qualitative analysis

- Qualitative analysis = simple observations, no numerical results eg.: formation of a precipitate, color change

TESTING FOR ANIONS

Carbonate test (gas)

Na2CO3 + 2HNO3 --> 2NaNO3 + CO2 + H2O         looking for CO3 2-

• Add nitric acid to solution tested
• If bubbles it could be a carbonate
• To prove that gas produced is = CO2

       -  bubble gas through lime water 

       - lime water will turn cloudy --- CO reacts to form white precipitate (CaCO3)

Sulfate test (precipitate)

BaSO4 is insoluble in H2O / When Ba2+ is added to a solution a precipitate is formed

Ba2+ + SO4 2- --> BaSO4 

Halide test (precipitate)

Ag+  + X- (any halide ion) --> AgX

• Add AgNO3 to an aq solution of a halide
• AgCl - white - soluble in dilute NH3   /   AgBr - cream-colored…