A Simple Demonstration of the Oxidation of Ammonia to Nitric Acid SAUL S. HAUBEN and RICHARD S . SIEGEL Brooklyn Technical High School, Brooklyn, Nero York
of demonstrations of the ANUMBER process have been described in THIS
Ostwald
JOURNAL.'
The authors have used these and other methods, but have found the following objections to them as teaching aids : (a) In some, the addition of pure oxygen is necessary. This needlessly complicates the demonstration for the students and is not a true picture of the process as carried out commercially. (b) Those demonstrations which involve electrical heating, we have found, confuse the pupils. Many of them get the idea that the electric current is necessary for the reaction to take place. (6) None of the demonstrations shows how the exothermic nature of the reaction is taken advantage of commercially.
The authors feel that the following method e l i i nates the above objections since i t employs only air and dry ammonia gas and, after the initial heating, utilizes the heat of reaction to cause the catalyst to function. The apparatus is easily assembled, entirely visible, and the chemicals are readily available. Procedure. Set up the apparatus as indicated in ' HAUT,J. CHBM.EDUC.,11, 575 (1934). HAZLEAURST, ibid..
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10, 639 (1933).
the diagram. Use enough platinized asbestos to fill about 5.0 cm. of the glass tube and keep in place with two wads of glass wool. (We used a soft glass tube 30.0 cm. long; internal diameter 2.0 cm.) Heat the portion of the tube containing the catalyst strongly for about two minutes with the Bunsen burner flame spread out by means of a wing top. While heating, apply strong suction from a water aspirator. Then pass ammonia gas, prepared by dropping concentrated ammonium hydroxide on sodium hydroxide pellets, a t the rate of one drop per one to two seconds. When the catalyst begins to glow, remove the flame. Brown fumes of nitrogen dioxide will be observed filling the Florence flask within two to three minutes. If the ammonia gas is passed through too quickly, white fumes of ammonium nitrate may be seen. The stopper may be removed from the Florence flask, 20 to 30 ml. water added and shaken -until the brown fumes disappear. The presence of nitric acid is shown by the litmus test and the brown ring reaction with ferrous sulfate and concentrated sulfuric acid. Prefiaration of the Catalyst. Medium-fine acidwashed asbestos fibers are soaked, with stirring, in a three to five per cent chlorplatinic acid solution. The excess solution is squeezed out and the asbestos heated to redness in a porcelain crucible or casserole with a Meker burner or, better still, in an electric mufflefurnace. If platinum metal is available, about 1.5 g. can be dissolved in about 40 ml. aqua regia and solution evaporated to about 10 ml.volume. Then dilute the solution with about 40 ml. water, stir and soak the asbestos fibers, and proceed as before.
