8.3 Qualitative analysis

steps of carbonate test

1) add dilute nitric acid

2) bubbles = could be carbonate

3) bubble solution through limewater. white precipitate formed = carbonate

molecular formula for reaction of aqueous sodium carbonate with nitric acid

Na₂CO₃(aq) + 2HNO₃(aq)= 2NaNO₃(aq) + CO₂(g) +H₂O(l)

steps of sulfate test

1) add barium chloride or barium nitrate

2) white precipitate formed = sulfate present as barium sulfate is very insoluble in water

ionic equation of the reaction of barium ions and sulfate ions

Ba²⁺(aq) + SO₄^2-(aq) = BaSO₄(aq)

steps of halide test

1) add aqueous silver nitrate, AgNO₃, to an aqueous solution of a halide

2) white precipitate - silver chloride. cream precipitate = silver bromide. yellow precipitate = silver iodide

3) add aqueous ammonia to test the solubility of the precipitate

observations of a precipitate of silver chloride + dilute aqueous ammonia

silver chloride dissolves and solution becomes clear

observations of a precipitate of silver bromide + concentrated aqueous ammonia

silver bromide dissolves and solution becomes clear

observations of a precipitate of silver iodide + concentrated aqueous ammonia

silver iodide does not dissolve and yellow precipitate remains

general formula of the reaction of silver and an aqueous solution of any halide

Ag⁺(aq) + X^-(aq) = AgX(s)

order of tests

carbonate, sulfate, halides

why is there a correct order for the anion tests

1) carbonate test looks for bubbling. neither sulfate or halide ions produce bubbles with dilute acid

2) sulfate test looks for white precipitate. barium carbonate is white and insoluble in water. may get incorrect conclusion

3) halide test looks for precipitate. both silver carbonate and silver sulfate are insoluble in water and will form a precipitate in this test. may get incorrect conclusion

steps of carbonate test on a mixture of chemicals

1) bubbles = continue adding dilute nitric acid until bubbling stops

2) all carbonate ions will then have been removed

steps of sulfate test on a mixture of chemicals

1) add an excess of barium nitrate

2) any sulfate ions will precipitate out as barium sulfate. filter the solution to remove the barium sulfate

steps of halide test on a mixture of chemicals

1) add silver nitrate

2) any carbonate or sulfate ions initially present have already been removed so any precipitate formed most involve halide ions

3) add dilute/ concentrated ammonia to confirm which halide is present

steps of ammonium ion tets

1) add aqueous sodium hydroxide

2) warm mixture using a Bunsen burner/ water bath

3) hover damp red litmus paper above solution. damp red litmus paper turns blue = ammonia is present