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Traditional physical chemistry laboratories too often consist of outdated experiments demonstrating irrelevant or trivial principles (e.g., freezing point depression). The primary purpose of the experiments is for the students to attempt to confirm a theory that has been presented in the lecture. Very often the results are poor, and the students spend much time writing reports with extensive rationalizations of why the experimental data do not agree with theory. This engenders a sense that science is something a student cannot do.
We believe that physical chemistry is less a series of laws and techniques than an approach in which physics and mathematics are applied to chemical systems. Our goal was to develop a unified two semester laboratory in which students learn the fundamentals of thermodynamics and kinetics through hands on, independent experimentation. Therefore we devised a series of new experiments based upon a combination of currently active areas of research in physical chemistry and more traditional experiments. Additionally, we have added computer data acquisition and video image processing to integrate data collection, processing, and report writing via three Macintosh computers (Quadra 800 and 2 IIvx's), each equipped with a Strawberry Tree A/D board. The Quadra 800 also was fitted with a Data Translation video digitization board to use with a Cohu camera and S-VHS VCR.
The first semester activities focuse on homogeneous systems. The students determine: (a) the resonance energy of azulene using bomb calorimetry and compare it to that of naphthalene; (b) the ideal gas constant, and; (c) the mechanism of the enolization of malonic and methyl malonic acid. They also perform several experiments based on the Belousov--Zhabotiinsky (BZ) oscillating reaction (1). These experiments demonstrate homogeneous reaction systems of varying complexity. We use the homogeneous BZ reaction to investigate the behavior of chemical systems when far from equilibrium and examine the dynamics of the reaction. Details of these experiments have been reported previously (1). The computer data acquisition allows the preparation of phase portraits and the collection of more quantitative data than is obtainable with a strip chart recorder.
The second semester's emphasis is on reaction-diffusion systems. The students study Liesegang rings(2), the unstirred BZ reaction (1), and traveling fronts of polymerization and conduct an independent project. Liesegang rings are spatial structures formed with counter current diffusion of insoluble ions in a gel. An image of target patterns of the BZ system taken at 60-s intervals in an unstirred petri dish is used to obtain the ring spacing relationship, which in turn is related to the diffusion of ions in the gel. The results are compared to Fick's law.
The power of digital image processing is shown in the figure of target patterns at 60-s intervals with the BZ system in an unstirred Petri dish. The front position can be readily tracked, and the front velocities accurately determined.
In the polymerization fronts experiment (3--5), benzoyl peroxide is dissolved in a monomer, triethylene glycol dimethacrylate (TGDMA). The test tube containing the solution is put in a fume hood behind a safety shield. The reaction is initiated by either adding a few drops of dimethyl aniline (DMA) or putting a heat source to the top of the solution. Polymerization begins and travels down the tube as a front. Students measure the time it takes the front to travel down the tube to determine the front's velocity. This measurement is repeated for various concentrations of initiator and the results compared to the steady-state model's prediction. The effect of heat loss and buoyancy-driven convection are studied.
The independent project is intended to coalesce the yearlong laboratory experience. The students design their own experiment based upon phenomena studied and write a proposal for its performance. After receipt of the instructor's approval, the experiment is conducted and the results presented to the class.
Overall, students learn thermodynamics with projects that are of current research interest. More importantly, they learn how to do experiments on complex systems with modern techniques.
This work was partially supported by grant (No. 9350792) from the National Science Foundation, Division of Undergraduate Education, Instrumentation and Laboratory Improvement Program.
Literature Cited
- Pojman, J. A.; Craven, R.; Leard, D. J. Chem. Educ. 1994, 71, 84--90.
- Sharbaugh III, A. H.; Sharbaugh Jr., A. H. J. Chem. Educ. 1989, 66, 589--594.
- Pojman, J. A. J. Am. Chem. Soc. 1991, 113, 6284--6286.
- Pojman, J. A.; Craven, R.; Khan, A.; West, W. J. Phys. Chem. 1992, 96, 7466--7472.
- Pojman, J. A.; Willis, J.; Fortenberry, D.; Ilyashenko, V.; Khan, A. J. Polym. Sci. Part A: Polym Chem. 1995, 33, 643--652.
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