Charles W. Clifford University
of California LOS Angeles
A Study of Ammonium Carbamate: A Student Project
I n connection with a project involving the relation of ammonium compounds to soil conditioning and plant growth, some compounds of ammonia and carbon dioxide were studied. Gaseous anhydrous ammonia and gaseous anhydrous carbon dioxide, reacting in various proportions a t room temperature and atmospheric pressure, gave only ammonium carbamate. Proportions used of NH3: COz were 1 :2, 1 :1, and 2: 1. The minimum flow rate of 77 ml/min was adjusted to maintain the desired proportions of gaseous reactants in the reaction chamber. The same compound, NHa COONH,, was produced by adding powdered solid carbon dioxide to liquid ammonia. The volatility of ammonium carbamate varies with temperature, average particle size, and other conditions, and is a definite factor in analysis. Volatility determinations should be made by duplicating temperature, time, and manner of air exposure involved in the an* lytical procedure, and the indicated corrections should be applied to samples. These products were analyzed by some or all of the following procedures, using about 0.15-g samples and 0.1 N HzSOaand NaOH: (a) By measuring the amount of ammonia released in the acidified solution. (b) By measuring the amount of Naf from NaOH required to replace NH4+in the (NH4),S04formed in (a).
104 / Journal of Chemicol Educofion
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Rv mine a cnnvent,iond ahmrnt,ion train to determine the
heated to approximately 5g°C, some analyses were made by very slowly heating samples to about 70°C,then weighing the NH, after absorption in concentrated H&OI and the COXafter ahsorp tion in one of the usual absorbents. These procedures were checked using properly-prepared ammonium sulfate, ammonium chloride, and sodium carbonate as standards, and were found to he satisfactory. In addition to volatility, other possible causes of any inaccuracy in analytical results are possible traces of the carbonate and/or the bicarbonate due to mutual convertibility of these and the carhamate, or due to contact of the sample with moisture in the air.
There are several challenges in adapting conventional methods to preparation and analysis of ammonium carbamate-enough to build up interest and test a student's ingenuity. For example, it was found that a good reaction chamber for the gaseous reaction is a plastic sack with an inlet tube reaching into each far corner. This permits occasional manipulation to prevent caking. Also, convenience and accuracy are increased by adaptation or design of a suitable reaction flask to contain the sample. The test to distinguish between carbamate and carbonate may be of interest; a project of this type may be used to encourage the habit of making preliminary literature searches and to provide a good experience in quantitative analysis.
