overhead projector
edited by DORISKOLB Bradley University Peoria, IL 61625
A Eutectic Mixture with Medicinal Applications Reggle L. Hudson, Vlckl Perez Osburn, and Robert Brashear' Eckerd College St. Petersburg. FL 33733 Few articles on eutectics have appeared in this Journal2in the nast 65 . vears.,desnite . the fact that eutectics are treated in virtually every undergraduate physical chemistry textbook and many physical and organic laboratory books. A survey of current introductory physical chemistry texts shows that while eutectic mixtures are treated a t various levels of detail, most examples presented are aimed toward eneineerina.. applications and hiph-temperature chemistry. .. ~ n f a c tthe , only commonly used-exampie of a eutectic cloie to room temperature seems to be the NaCI-ice system, one with which most students arealready at least casually familiar. We have found that the menthol-~henol eutectic has some important advantages for classroom use. First, it fills a ean - . in the textbooks bv. providine . - an example of a roomtemperature eutectic that is new to students. Second, this euterric ran be used as a simple demonptration. Finally, the menthol-phenol mixture provides an example of the application of eutectic science to medicine since this particular eutectic is used for the relief of itching and is dispensed in ointments for such purpose by pha~macists.~ This medicinal application is an important motivator in classes with substantial numbers of life sciences majors. The menthol-phenol eutectic can be presented in several ways. I t can simply be mentioned during a lecture or i t could be developed as a laboratory project, although we have not pursued the latter. At Eckerd College we have found this eutectic svstem to be an excellent overhead demonstration. Crystals of menthol (mp 44 'C) and phenol (mp 41 OC) can be placed on two sides of a Petri dish on an overhead projecin tor. When a few crystals of each compound are contact in the center of the dish, liquefaction is obvious in a
' Registered Pharmacist. Fedco Discount Drugs, Inverness. FL.
(a)Copley, G. N. J. Chem. Educ. 1959, 36,596; (b) Petrucci, R. H. J. Chem. Educ. 1959, 36,603; (c) Viswanathan. A. J. Chem. Educ. 1960, 37, A361; (d) Wise, J. H.: Shillington, J. K.; Wan, W. J.; Whitaker. R. D. J. Chem. Educ. 1964, 41, 96; (e) Petrucci. R. H.; Melnyk, A.; Muller. 0. J. Chem. Educ. 1965, 42,362: (f) Karunakaran, K. J. Chem. Educ. 1976,53,676: (g)Blanchetle, P. 6. J. Chem. Educ. 1987, 64, 267. For a recent call to reinstitutedemonsirationsin physical chemistry classes, see Crosby, G. A. In Essays in Physical Chemistry; American Chemical Society: Washington. DC. 1988: p. 7. (a)Physicians Desk Reference: Huff, 6.. Ed.: Medical Economics: Oradell. NJ. 1974; (b) The Merck Index; Windholtz, M., Ed.; Merck: Rahway, NJ. 1976. Sources consulted were (a) Stephen, H.; Stephen, T. Solubilities of inorganic and Organic Compounds: Macmillan: New York. 1963: Vol. I, Part I; (b) Journal of Physical and Chemical Reference Data (vols. l-present. 1972-present); (c) BuiIetin of Chemical Thermodynamics (vols. 14-present, 1971-present): (d) International Critial Tables of Numeric Data. Physics, Chemisiry, and Technology; McGraw-Hill: New York. 1926; (e)various editions of Lange's Hancb book of Chemistryand the Chemical Rubber Company's Handbook of Chemisiry and Physics.
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156
Journal of Chemical Education
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minute or so, often sooner. Furthermore. the chance from solid to liquid is easily seen on a projection screen,eren from the rear of a large lecture hall. We have used this domonstration successfuliy in both general and physical chemistry classes. Since our literature searches failed to uncover details concerning the menthol-phenol s y s t e q 5 we have made a few thermal and spectroscopic measurements on menthol-phenolmixtures. Our cooling curves for various mixtures lead to a eutectic composition of approximately 50 mol % menthol and a eutectic temperature around -30 OC. NMR and IR evidence of shifts in O-H absorptions suggest hydrogen bonding between molecules in the eutectic, as expected. The authors will be pleased to hear from readers with information on this and other medically related eutectic mixtures.
The Human Salt Bridge Plrketta Scharlin' University of Turk" Turk". Finland
Rubln Battlno2 Wright State University Dayton. OH 45435
A common electrochemistry demonstration involves pushing a strip of zinc and one of copper into a fruit like an orange, apple, or lemon or into a vegetable like an onion, carrot. or tomato.3 The Edmund Scientific Co. sells a notato clock ( # ~ 3 4 , 3 5 7$19.95) that runs with the h e l p ~ f ~ o i a t o e s , fruits or vegetables, and even soda pop or beer! We found that the human body works, too. An interesting historical note is that Volt& is said to have experienced an "unpleasant taste" when he joined a bit of tinbn the tip of his tbngue to a silver spoon resting further back. In this paper we describe a simple device designed for use on an overhead projector to illustrate the "human salt bridge". The device that is shown in the figure is made of a %-in.thick Plexiglas base plate that is 7.5 X 10 in. Ten pairs of electrodes are mounted side by side on the base. The 10 electrodes on each side are all attached to a copper bus bar that is in turn connected to a dual banana jack. The electrodes are approximately %a X % X 2 in. Transfer letters placed on the base indicate the electrode material used. Our initial set of 10 electrodes was: Cu, Ag, Pb, Fe, Cd, Mg, Zn, Al, C, and Ni. Other interesting electrode materials would be: brass, Sn, Cr, W, Pt, Pd, Mn, Co, and Au. For the more
' Visiting Associate Professor.1988-1989, Wright State University.
To whom correspondence should be addressed. Ensman. R.: Hacker, T. H.; Wentworlh. R. A. D. J. Chem. Educ. 1988, 63,277. Cited by Heilbron. J. L. In Gillispie, C. C., Ed. Dictionary of Scientific Biography: Swibner's; New York, 1976.
Some Results 01 the "Human Salt Brldge" Demonstration Uslng Copper as the Common Electrode Potential in volts Mher metal electrode A1
-0.92
Fe
-0.11
Pb
-0.36 -0.62 -1.18 0.09 -0.36 0.00 -0.11
Zn
Electrode Oevice.
Mg Ag
Cd C
expensive materials, wires may be used. The size of the base plate was chosen so that i t could easily fit on a n overhead projector with a projection overhead voltmeters. Dual banana plugs connect the battery to the voltmeter. Procedure Place the device and the voltmeter on the overhead projector. Then, using your thumbs, rub and press the copper electrode on one side and the second electrode on the other side. Students can record the voltage and sign for each electrode vs. copper as the demonstrator successively rubs and presses on each electrode. Reversing sides reverses the sign of the emf. You can readily construct an "activity" series in this demonstration. Contact resistance and varying amounts of moisture on
Barnen, 8.; Pollock, J. A,; Banino, R. J. Chem. Educ. 1986, 63, 460.
Right-hand Cu electrode
Ni
Len-hand Cu electrode
0.94 -0.04 0.36 0.56 1.06 -0.13 0.27 -0.10 0.10
your fingertips cause the voltages t o vary somewhat. However, multiple measurements show a standard deviation of about 0.02 to 0.04 V depending on the electrode pairs used. An attempt to reduce this error hy soaking apiece of clothesline in electrolyte gave no better results than the use of fineers. The electrodes must be clean! The table gives some typical results using the left-hand and also the rieht-hand comer .. electrode vs. the indicated electrodes. There are some interesting variations. Of course, touching the same material on both sides gives zero volts. ~
~. ~
Acknowledgment P. Scharlin gratefully acknowledges grants from the Finnish Cultural Foundation and the Academy of Finland.
Chemistry in ~ction! "The Periodic Table Videodisc: Reactions of the Elements" "The Periodic Videodisc: Reactions of the Elements" is a 30-min videodisc containingaction sequences and still shots of each element: in its murt common form, rencring w~thsir, reactinx with water, reacting with acids. reacting with hasp. and in some common user and applirationr. The videodisc has been puhlrshed as Sperral Issue 1 uf Journol bf ('hemtcol Education. Snlrware and mav he urdered for $:fit955 fureirnr. Purchasers will receive a single-sided.CAV.tvoe videodisc and a Video 1mage~irectory;whichisanindexed iist of eodesfromwhich toseleet frames,&her for use with; hand-operated, remote-controldevice or for writing one's own computer control programs. Those who purchased Volume IB2 of JCE: Software: "KC? Discoverer" also received a program that allows them to control the videodisc through their MS-DOS compatible computers. Further details about the videodisc may be found on page 19 of the January 1989 issue of this Journal. To order: fill the out the form below; make a check or money order payahle to JCE: Software, Department of Chemistry,Eastern Michigan University, Ypsilanti, MI48197. Payment must he in U.S. funds drawnon a U.S. hank or by international money order or magnetically encoded check.
Order Form Please send me the following: lM Periodic Table Vldeodsc: Reactions of ihe Elements: $50 ($55 foreign). Includes videodisc and index of code numbers to hamea on the disc.
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Volume 67
Number 2
February 1990
157
