With flask A filled with Bra vapor, adjust the pressure in B to about 21 cm, the vapor pressure of liquid bromine at room temperature, and open 83 and 86 The diffusion of Bra into flask B is very slow indeed, providing a clahs demonstration of several weeks duration. Do not ruin a manometer by trying to read pressures! Saturated Vapor Pressure; Diffusion. Using suitable phials (see Fig. 3) containing about 1ml of liquids such as water, ether (caution), acetaldehyde, petroleum ether, etc., the saturated vapor pressures of these substances may be found. With a phial attached a t inlet Pi, flask A is evacuated, the phial is opened to the system, and the vapor pressure is read at intervals, until equilibrium is attained. Initial cooling of the liquid, resulting in condensation of moisture on the tube, is often observed. Data for other liquids may be obtamed in a similar way. Saturated vapor pressures at O0 or -16'C may be obtained by placing ice or ice/salt baths around the phial at Ti. Errors due to the presence of air in the phial should be noted. This may he eliminated by pumping off the first two or three samples of "vapor." It is instructive to try to recondense the vapor back into the phial, using liquid nitrogen or an isopropyl alcohol-dry ice bath (-7S0C). The presence of quite small amounts of non-condensible gases (N2, Oa) dramatically impedes the diffusion of vapor back into the phial. Molecular Weight. Attach a phial containing ether (or other volatile liquid, 1-2 ml) a t Pi, cool in a liquid nitrogen or an isopropyl alcohol-dry ice bath and remove the air from flask A and from the phial. Remove the phial from the system, warm to room temperature, and weigh. Attach at PI, evacuate, isolate flask A and open the phial to permit ether vapor to fill the flask
(10-20 cm pressure). Rcad the pressure, reweigh the phial to find the weight of vapor, and calibrate the volume of the flask by filling with water from a measuring cylinder. The molecular weight of the vapor is calculated, being the weight of STP vapor that would occupy 22.4 1. Heat of Reaction; Reaction Stoichiometry. Using lecture bottles, introduce gaseous ammonia into flask A via Pi (e.g., to 30 cm pressure), and a somewhat greater amount of hydrogen chloride into B via P2(e.g., 40 cm pressure). When S e and 8 8 are opened, the gases should mix and react in flask A, producing a white smoke of NHiCl. The walls of the flask become quite hot as a result of heat liberated during reaction. The pressure of unused HC1 should be read and the stoichiometry of the reaction determined. There are many modifications to the preceding experiments, all of which require interpretations based on the molecular concept of matter. Without too much difficulty, principles or concepts such as the Gas Laws, molecular motions, degrees of freedom, mean free path, gaseous diffusion, molecular collisions, temperature, specific heat, latent heat, thermal and radiant energy, equipartition of energy, heats of chemical reactions, reaction stoichiometry, Avogadro's Law, constancy of composition, and many other related aspects may be illustrated by or used in the interpretation of such experiments. Acknowledgment
The authors gratefully acknowledge many inspirational discussions with Professor B. D. Pate and colleagues, whose classroom adventures kindle curiosity, excitement, and interest in chemistry.
Summer Studies in Chemistry for Students Regularly Matriculated at Ill-Equipped Colleges In the summer of 1967, the Memphis State University Department,'of Chemistry, under a grant from the Special Projects Program of the National Science Foundation, instituted a program of formal undergraduat,e course work for student,^ who were in regular attendance at illequipped colleges in the Southeast Unit,ed States. Since the program's original publicity, we have been contacted by other universities with thoughia of putting into action similar plans. Therefore, the following description is presented for the benefit of anyone interested. In brief, the program consists of upper-division chemistry courses presented exclusively for the participants, but of the same nature as the courses required by the University of its own candidates for the Degree of Bachelor of Science in Chemistry. In addition, and most importantly, the students earn regular college credit transferrahle to their "home" colleges. In this way their degrees are strengthened from their "home" colleges but in no way are theseparate identities of the colleges endangered. The maintenance of separate identities raised a matter of some concern during the early stages of the proposal development. This was the means by which the colleges whose students would be invited to participate would be assured that the intent of theprogramwas to strengthen the students' degrees from their colleges rather than t o proselytize them for the University. The dedication of the college representatives contacted to t,he welfare of their students served to belie this concern. ROBERTF. WATSON MEMPHISSTATEUNIVERSITY MEMPHIS,TENNESSEE 38111
Volume 45, Number 1 1, November 1968
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