THE PREPARATION OF LIQUID AMMONIA AS A LABORATORY PROJECT ROBERT L. HERD, 1016 SAINT PAULSTREET, BALTIMORE, MARYLAND The reactions and properties of liquid ammonia are often discussed in chemistry classes, but, unfortunately, an objective study of this subject is rarely undertaken. This is perhaps due primarily to the inaccessibility of liquidammonia in sufficiently small quantities for laboratory demonstrations. Also, the liquid is difficult to handle under ordinary conditions. In the suggested study herein described, these difficulties have been overcome. In addition, apparatus has been used which may be readily secured from equipment available in the average general chemistry laboratory. The study may be used as a project for students, as a demonstration experiment, or as a preparation in an advanced course. Materials and Apparatus Set-Up The essential details of apparatus required and the arrangement of it are revealed in the accompanying diagram, but a few suggestions regarding i t may be of value. The safety tube, A, filled with mercury to a height of 5 cm., is used to prevent an unduly high pressure being developed within the apparatus in the event that the drying tube, F, should become clogged. The asbestos board, D, is inserted to protect the cooling chambers and to keep the flame away from the alcohol and chloroform solutions. A straight inner tube of a condenser serves very well for the drying tube, F. Tubes F and H may be filled with soda lime, since this material is readily available. Other drying agents may be used (1). The condensing chamber, K, may be made by cutting the bottom from an ether can, and fitting the end of a glass coil, L (the inner coil from a broken condenser is quite suitable), through the mouth by means of a closely fitting cork. By surrounding the can with sheet asbestos, the efficiency of the condenser will be increased. The receiving flask within the beaker, M , may be made by cutting the top off a graduated cylinder. The volume of liquid ammonia obtained may thus be read directly. All connections should be air-tight and care should be taken to prevent moisture from condensing with the ammonia. Operation When the apparatus is assembled, ready for operation, solid ammonium chloride, sufficient to yield the quantity of liquid ammonia sought, is introduced into the reaction flask, C. Condenser K is filled with chloroform until the major portion of the coil, L, is submerged. Small portions of solid carbon dioxide are then slowly added to the chloroform until strong 2062
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ebullition subsides. At this point the temperature of the bath should be sufficiently reduced to freeze mercury. An excess of solid carbon dioxide is kept in condenser, K, throughout the reaction. Beakers M and P are filled similarly with alcohol and solid carbon dioxide. Alcohol instead of chloroform is used in M , since with the latter a frozen moisture, which obscures the gradations on the receiving cylinder, is produced. Beaker, E, is filled with a water and ice mixture.
A-Mercu~y safety tube B-Dropping funnel C-Reaction flask I)--Asbestos board E-Ice-ooled condensing chamber for moisture F-Drying tube, approximately 30 m., filled with soda lime C T - T u b e connection H-Drying tube, filled with soda lime J-Aspirating bulb
K-Chloroform and solid carbon dioxide cooled condensing chamber for ammonia L-Condensing coil for ammonia gas M-Alcohol and solid carbon dioxide cooled collecting chamber for liquid ammonia N-Delivery tube far liquid ammonia &Drying tube, filled with soda lime P-Alcohol and solid carbon dioxide cooled Forage chamber for liquid ammonia
To generate the ammonia, gradually add concentrated sodium hydroxide from dropping funnel, B, to ammonium chloride. As the reaction proceeds, apply heat to the reaction flask, C, until all the ammonia is driven off. By passing the ammonia through condenser, E, most of the moisture is removed before the gas enters the drying tube, F. The ammonia is condensed while passing through the coil, L, and is collected in the graduated cylinder in beaker, M. In order to watch the progress of the volume of
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ammonia being obtained, the frost which collects on the sides of the beaker, M , may be washed off with alcohol. Removal and Testing of Liquid Ammonia To remove small amounts of the liquid ammonia from the cylinder, lower tube, N, until the end is well below the surface of the liquid, place the aspirating bulb, J , on the drying tube, H, and remove drying tube, 0. Aspirate the liquid into clean dry test tubes immersed in the bath, P, of alcohol and solid carbon dioxide. (Tight-fitting corks should be provided to close the tubes immediately.) After aspiration, drying tube, 0, should be replaced to prevent moisture entering the receiving cylinder.* The reactions of liquid ammonia may be demonstrated as described in EDUCATION (2). previous issues of the JOURNAL OF CHEMICAL From four mols of ammonium chloride, 82 cc. of liquid ammonia, which represents a 75% yield, were obtained. After the apparatus has been set up, sufficient liquid ammonia for the demonstration of several reactions may be obtained easily within an hour. Objectives Some of the objectives brought to the attention of the students by a study of this project are: 1. 2. 3. 4. 5. 6.
Study of the reactions and properties of liquid ammonia. Observations a t lower than ordinary temperatures. Practice in the calculation of yield. Study of liquid ammonia in refrigeration. Separation of a gas from a liquid. Study of the properties of carbon dioxide. 7. Liquefaction of other gases. 8. General review of properties of gases.
Literature Cited 1
COOPERAND HENSHAW, "Dehydrating Ammonia Vapors," Chem. AbsC., 22, 1018 (Mar. 20, 1928); COOPER,HENSHAW, AND W. C. HOLMES & CO., LTD.,"Separating , AND Water Vapor from Ammonia," ibid., 22, 1833 (May 20, 1928); S ~ r r sSWART, BRUIN, "The Influence of Intensive Drying on Inner Equilibria," ibid., 24, 2348 (May 20, 1930); "Activated Alumina," J. CHEM.EDUC.,7, 2989 (Dec., 1930). (2) J O H N ~ O AND N FERNELIUS. "Liquid Ammonia as a Solvent and the Ammonia System of Compounds. V. The Properties of Solutions of Metallic Compounds in Liquid Ammonia," J. CHEM.EDUC.,7,981-99 (May, 1930).
* Any suitable flask may be substituted for the graduate cylinder, and the liquid ammonia may be poured out rather than aspirated without taking up too much moisture t o intelfere with the reactions t o be demonstrated.
