If it is not soluble in cold water, try heating up the solution by passing it though a Bunsen burner flame. Precipitation Test Use the solubility table to find a suitable counterion that will form an insoluble substance with one of the possible compounds and a soluble substance with the other one. You will have to distinguish between the compounds based on their cations since the anions are the same for both. Some ions will form a gas upon the addition of a suitable reagent. Perform these tests by adding the most concentrated reagent available to a few crystals of the solid unknown.
Heating is sometimes necessary to form the gas in quantities that can be detected.
You must heat the reaction mixture at the same time that you try to detect the gas. Oxidation Test Potassium permanganate can be used to distinguish between a substance that is easily oxidized and one that is not. For example, it could be used to distinguish between ferric and ferrous ions. To perform this test, dissolve a few crystals of your unknown in about 12 drops of water in a test tube, add HCl until the solution is acidic to litmus paper and then add two drops of the permanganate solution. This test will distinguish between chloride, bromide and iodide anions.