JOURNAL OF CHEMICAL EDUCATION
A QUALITATIVE TEST FOR AMMONIA IN AQUEOUS SOLUTION RICHARD C. O'NEIL and W. 8. RENFROW Oberlin College, Oberlin, Ohio
THEreaction between ammonia and iodine1 is well known, but apparently has not been utilized for detection of ammonia. We have found that this reaction affords a reliable test for ammonia which is more convenient than the usual methods of detection.= One milliliter of unknown solution is neutralized to the litmus end point and two drops excess of 10 per cent sodium hydroxide solution added. . Any precipitate which forms is removed by centrifuging. The clear solution is poured onto about 3 mg. of iodine on a spot plate. A crystal of iodine is pushed to the surface of the
' SIUGWICK, N. V., "Chrmical Elurnenta and Their Compauntls," Oxford Press, London, 1950, p. 707. FURMAN, N. H. "Seott'a Standard Methods of ChemiealAn& ysis," 5th ed., D. Van Nostrand and Co., New York, 1939, p. 630.
liquid with a stirring rod and allowed to slide to the bottom of the depression in the spot plate. A black, finely divided precipitate appears in the wake of the iodine crystal. With small concentrations (30 mg./liter) of ammonia, the black precipitate dissolves within a few seconds. When the concentration of ammonia is relatively high (500 mg./liter) the precipitate is more copious and persists much longer. The test has been used successfully on a variety of solutions issued as unknowns in an elementary course in qualitative analysis and no interference by other ions has been discovered. The black precipitate formed in the test is highly explosive when dry and should be destroyed by adding sodium hydroxide or by washing down a drain.
