Testing for Anions
Ion CO32-, carbonate is found in limestone, or calcium carbonate (CaCO3).
To test for it, you must first: Add a dilute acid to the sample. A gas is given off which when tested, should prove to be carbon dioxide.
Sulphate and Sulphide
Sulphate is SO42- and
Sulphide is SO32-
Adding barium chloride to the solution you are testing a white precipitate will form. If you add hydrochloric acid, the sulpahte (SO42-) WILL NOT dissolve and the sulphite (SO32-) will.
The test for halogens, or halide ions, is to add silver nitrate to a solution. We often add some nitric acid first as well. If there are chloride, bromide or iodide ions in the soltion they will react with silver to form a precipitate. The different precipitates are summarised in the table below.
The ionic equations for these reactions are:
Ag+ (aq) + Cl- (aq) AgCl (s)
Ag+ (aq) + Br- (aq) AgBr (aq)
Ag+ (aq) + I- (aq) AgI (aq)