I
dild by:
WALTER A. WOLF Colgote University Hamilton, New York
Equilibrium-A
and/or two component mixtures. The inclusion of a colored solution in the solution to be distilled enables the instructor to encourage and monitor careful laboratory technique by checking for the presence of stains on students' hands, clothing, benches and color in the receiving flask. Indigo can be used in organic solvents, while permanganate (0.001M) can be used in aqueous solutions.-C. J. Bier, University of North Florida, Jacksonville, Florida 32216. 2) A common general chemistry laboratory experiment to illustrate the Law of Multiple Proportions involves the thermal decomposition of CuBrz to CuBr and Brz. The Brz produced is passed into a large flask that is partly filled with water, but considerable Brz escapes into the laboratory air. We have made this experiment much safer by using a 1% aqueous solution of sodium thiosulfate to consume the BIZ and by placing a cotton plug around the delivery tube a t the neck of the flask. This system could also he used for Clz absorption. The analogy to proper treatment of industrial wastes is made for the students.-Joseph E. Schiller, Merch College of Detroit, Detroit, Michigan 48219. 3) Many college radio stations regularly receive and air the "Men and Molecules" programs. We have found an additional use for these programs. A group of beginning chemistry students were instructed to use the tapes as a source of ideas for a required oral report. Tapes were played upon the station's equipment. Preparation for the oral report was completed with additional library work. -Frank W. Hengeveld, Dana College, Blair, Nebraska 68008. 4) Students in general chemistry laboratory can readily be taught solution concentrations, weighing and volumetric techniques with the following experiment. CuS04.5H20 has an absorption maximum at 725 nm, which can he used to check the student's work on a spectrophotometer. A calculation of the amount of solid needed to prepare 50 ml of a 0.2 to 0.7 M solution is made. This value is checked by the instructor and when correct the student is permitted to weigh out this material and prepare the solution. Then the absorbance is measured and compared to that on a working curve. The student is required to repeat the experiment once or until he obtains satisfactory results. Additional challenge can he added by requiring dilutions of the original solution.-Herbert L. Smith and John P. Kames, Slippen, Rock State College, Slippery Rock, Pennsyluania 160.57.
Novel Classroom Demonstration
Gordon F. Hambly John Abbott College P.O. Box 2000 Ste. Anne de Belleuue Quebec, Canada The concept of a reaction proceeding in two directions, eventually reaching the equilihrium point, and of a constant relating concentration of reactants and products a t the equilibrium point is difficult to grasp for some students. The following demonstration was designed to meet this need and add a little excitement to the lecture. A relatively large area is cleared of chairs, tables, etc. If space is a problem, a small number of students can be selected. The students are divided according to sex and they are told that this is a contest between Mr. and Ms. Each student is handed 2 styrofoam halls and the object of the game is to try to get as many of the halls as possible on the opponent's side. The rules are as follows: (1)the 2 groups are separated by at least 5 yards; ( 2 ) everyone must throw 1 ball a t a time with their right hand; (3) the ball must be thrown t o any opponent so that it is capable of being caught (fasthalls are not allowed) and (4) each group is allowed to arrange themselves in any formation (maintaining at least a 5-yard separation from their opponents) before the contest starts, hut once they have chosen a formation they can not vary it. At the whistle, the throwing begins and is allowed t o continue for one minute a t which time the styrofoam balls on each side are counted. The throwing is then continued for another minute and the halls on each side are recounted. This procedure is then repeated giving one side, and then the other side, all the balls initially. The equilihrium concentration is attained within one minute and the styrofoam ball counts in the 4 runs are almost identical. In addition to realizing that the equilihrium concentration can be approached from either side, the student is able to "see" the dvnamic a s ~ e cof t eauilibrium. Rule (4) is necessary because a more efficient formation adapted hetween runs would alter the equilihrium position.
Compact Compacts 1) Introductory general and organic chemistry lahorato-
ries often include an exercise in the distillation of one
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Volume 52,Number 8. August 1975 / 519
