The sodium iodide in acetone test is performed to test an unknown sample for the presence of halides. If a white precipitate is formed at the end of the test, it indicates the presence of halides.
In order to test for the presence of halides, a 15% solution of sodium iodide in acetone is mixed with the unknown sample and shaken well. If no precipitate forms, the solution can be heated up to 50 degrees Celsius. If heated above this temperature, the acetone will evaporate and leave a white precipitate of sodium iodide, which is a false positive.
After heating, if a precipitate is still not observed, the solution should be cooled back down to room temperature. If a white precipitate forms, it indicates the presence of a halide due to the formation of a sodium halide salt. Since sodium salts of halides such as chloride and bromide salts are insoluble in acetone, they appear as precipitates.