Bubble gas through limewater to test for CO2 – will turn limewater cloudy
Fizzing due to CO2 would be observed if a carbonate was present
Testing for presence of a sulfate
Acidified BaCl2 solution is used as a reagent to test for sulfate ions
If barium chloride is added to a solution that contains sulphate ions a white precipitate forms
Other anions should give a negative result which is no precipitate forming
The acid is needed to react with carbonate impurities often found in salts -form white barium carbonate precipitate and give a false results
Sulfuric acid cannot be used to acidify the mixture because it contains sulphate ions which would form a precipitate
Testing for halide ions with silver nitrate.
This reaction is used as a test to identify which halide ion is present. The test solution is made acidic with nitric acid, and then silver nitrate solution is added dropwise.
The role of nitric acid is to react with any carbonates present to prevent formation of the precipitate Ag2CO3 . This would mask the desired observations
The sequence of tests required is carbonate, sulfate then halide. (This will prevent false results of as both BaCO3 and Ag2SO4 are insoluble.)
