Halide ions in solution (chloride, bromide and iodide) are identified with silver nitrate solution. First the sample is acidified with dilute nitric acid, then silver nitrate solution is added. The acid removes carbonate ions, which would also form a precipitate with silver ions and give a false result.
Silver ions react with halide ions to form an insoluble silver halide, which appears as a precipitate. The colour tells you the halide. Silver chloride is white, silver bromide is cream and silver iodide is yellow.
The ionic equation for chloride is Ag+(aq) + Cl-(aq) → AgCl(s). Bromide and iodide ions react in the same way. The cream and yellow colours can be hard to tell apart, so compare carefully.
