For the silver nitrate test, the solution is added first with nitric acid. This test is to determine halide ions. When silver nitrate is added to the solution, the color of the precipitate would indicate the identity of the ion. For chloride ions, the precipitate is white.
For the sodium thiosulfate test, chlorine is treated with Ki solution which turns brown. When it is titrated with sodium thiosulfate solution, the brown turns yellow upon which, starch is added. It forms a complex which appears as dark blue. Upon adding more titrant, it reaches the endpoint where the blue turns colorless.
