To 1 mL of the sodium iodide in acetone reagent in a test tube add 2 drops of the compound whose elemental analysis showed the presence of chlorine or bromine. If the compound is a solid, dissolve about 0.1 g in the smallest possible volume of acetone, and add the solution to the reagent. Shake the test tube, and allow the solution to stand at room temperature for 3 min. Note if a precipitate is formed and also if the solution turns reddish brown because of the liberation of free iodine. If no change occurs at room temperature, place the test tube in a beaker of water at 50oC. Excessive heating causes loss of acetone and precipitation of sodium iodide, which can lead to false positive results. At the end of 6 min, cool to room temperature and note if a reaction has occurred.
Sodium Iodide in Acetone Reagent: Fifteen grams of sodium iodide is dissolved in 100 mL of pure acetone. The solution, colorless at first, becomes a pale lemon yellow. It should be kept in a dark bottle and discarded as soon as a definite red-brown color develops.
Production of solid sodium chloride or sodium bromide is a positive test.
Excessive heating can cause the loss of acetone and the production of solid salt leading to a false positive test.
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