In the Laboratory
An Introductory Experience for Physical Chemistry: Victor Meyer Revisited
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Frederick A. Kundell* Department of Chemistry, Henson School of Science and Technology, Salisbury State University, Salisbury, MD 21801
Overview This introductory physical chemistry experiment has three components. 1. The evaluation of the random experimental error in several common experimental measurements. 2. The Victor Meyer determination of the molecular weight of a volatile liquid using an update of the procedure proposed by G. W. Drake in 1963 (1). 3. A detailed write-up on the treatment of experimental error.
We have been using modifications of this of this experiment for approximately 20 years. Since this introductory experience works so well for us, we thought others might find it of interest. In addition to a relevant ideal gas experiment, it gives students, in writing, an introduction to the statistical treatment of error and its propagation in computations. The statistical error section is a student-level presentation based on the procedure of Guedens et al. (2). The statistical error treatment section of this experiment can serve as a reference throughout the course, or, if the experiment is not used, the statistical error treatment section can be extracted from the experimental write-up and used as a handout. The Specific Advantages of This Introductory Experience The introductory coverage in an experimental physical chemistry or an advanced experimental laboratory experience often includes the statistical treatment of experimental error and an ideal gas experiment as two separate topics. Our approach brings these two topics together. In so doing, students have an opportunity to: 1. Determine the extent of error in some common measurements. 2. Begin the course with an enjoyable group experiment. In addition, the modified Victor Meyer experiment using acetone is an excellent demonstration of ideal gas behavior.
W Supplementary materials for this article are available on JCE Online at http://JChemEd.chem.wisc.edu/Journal/issues/1999/ Apr/abs542.html.
*Email:
[email protected].
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3. Determine the molecular weight of a volatile liquid. The modified Victor Meyer experiment, when done precisely, can produce very good results for acetone (see VMinstructor online, for specifics). Beginning experimental physical chemistry students, working together, do not normally achieve this degree of precision and accuracy. 4. Collect sufficient data for their statistical treatment of experimental error; in so doing, students feel a sense of ownership of the data. The data acquisition is sufficiently fast to allow a class to collect a sizable data set (15 to 20 readings) in a relatively short period of time (approximately an hour). 5. Work on a data set that contains theoretical, systematic, and random error. 6. Work on an experiment that contains essentially no chemical hazards. The only chemicals used are water and a small amount of acetone. 7. Do an experiment that is easily understood and computationally straightforward.
We feel that this exercise provides an excellent introduction to experimental physical chemistry or an advanced experimental course. The online presentation contains six files, the contents of which are:W 1. VMinstructor. The introductory presentation for the instructor. 2. VMexp.The laboratory presentation for the students. 3. VMFig1. Figure 1, the modified Victor Meyer Apparatus (to be used also as instructions for the glass blower). 4. VMFig2. Figure 2, the experimental setup. 5. VMForm1. The data form used by the students in Part 1. 6. VMForm2. The data form used by the students in Part 2.
We would welcome your comments and suggestion regarding this presentation. Literature Cited 1. Drake, G. W. J. Chem. Educ. 1963, 40, 606. 2. Guedens, W. J.; Yperman, J.; Mullens, J.; Van Poucke, L. C. J. Chem. Educ. 1993, 70, 776–779 and 838–841.
Journal of Chemical Education • Vol. 76 No. 4 April 1999 • JChemEd.chem.wisc.edu
