Detection of Halides G. W. THIESSEN, K. M. BECK, and A. E. SMITH Monrnouth College, Monrnouth, Illinois
I N BEGINNING inorganic qualitative analysis or even freshman general chemistry there is often occasion to have the student identify the anion of a halide. A simple means of doing this is to concentrate the halide if i t is in solution by acidifying the solution with nitric acid and precipitating it with silver nitrate, decanting, and oxidizing the silver halide to give a free halogen. The halogen is then volatilized and identified by color, odor, and action on litmus paper. (Chlorine and bromine will bleach moist litmus paper and iodine will turn the paper gray due to the formation of crystals on it.) The halogen may also be condensed by passing it through a glass tube inserted in a stopper in the test tube into a cold receiving vessel and thus be identified. The oxidation is accomplished by mixing 0.3 to 0.4 g. of the wet silver halide precipitate with 0.1 to
0.2 g. of manganese dioxide in a test tube and adding 2 to 3 ml. of concentrated sulfuric acid. The test tubeis warmed over a flame and the free halogen comes off as a gas which can be readily identified by its color. The test can he applied to qualitative organic analysis when a Beilstein or sodium fusion test shows a halogen present. The halide is concentrated from the sodium fusion liquid with silver nitrate, and the silver salt is oxidized. Although this procedure is not applicable to a mixture, there are more meticulous standard methods for such. This method has the advantages of being quick and simple, and requiring no special apparatus. It is superior to the standard chlorine water test usually employed in freshman courses because it gives a positive test for the chloride.
