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WALTER A. WOLF Colgate Unlverslty Hamlltan. New York
The Use of an Eskimo YO-YOto Demonstrate Circular Dichroism and Optical Rotation Clifton E. Meloan Kansas State University Manhattan, Kansas 66506 a n d Dennis Gere Hewlett-Packard Company Philadelohia. Penmvlvania We have found that an Eskimo yo-yo can be used to more rlearlv illustrate the orinciole of ootical rotational in eenrral and &e difference between circuiar dichroism and optical rotary dispersion in particular. An Eskimo yo-yo consists of two felt or leather balls about 2 inches in diameter connected to each other with a string. Thestring isgrasped between the thumb and forefinger just off center. The hall on the "long string" rotates in a circular motion in one direction and the other ball rotates in the opposite direction. The hand holding the two halls must move up and down to keep the yo-yo in operation. At this stage we are illustrating the electrical component of normal radiation: i t is made of a right circular component and a left circular component and the resultant is a vertical oscillation of the field-the wave motion of a ray of radiation. By changing the relative string lengths, and the relative velocities, the differences between circular dicbroism and optical rotatory dispersion can be illustrated. Photos, diagrams and a more complete explanation are available from the authors.
Automatic Potentiometric Titrations Chester A. Pinkham Brownlee Field Tri-State University Angola, Indiana 46703 In our instrumental analysis course we performed a potentiometric titration on a chloride-iodide mixture by means of a point-by-point titration.' This was an extremely time consuming experiment, and the iodide equivalence point was frequently missed while the students were still learning the procedure. Thus, we decided to automate this experiment. A constant flow buret2 with a 2-1 separatory funnel as upper reservoir was used. The reference and indicating electrodes were connected to avariable speed Heath recorder. A potentiometer was connected across the input leads of the recorder. Samples of NaCl were run to calibrate the flow rate of the buret. The flow rate was reported in units of moles of AgN03/ min from measurements of distance to the equivalence point on the chart paper. Sample weights of NaCl from 0.01-0.08 g and a 0.01 M AgN03 solution were employed. A relative
standard deviation of 1.1% was obtained with the known samples. After the calibration, mixed samples of KI-NaCl were run as unknowns. The student results from this automated method were equivalent to the previous laborious titrations. Other advantages include the greater speed of the automated procedure and the low cost of the apparatus. 'Christian, G., "Analytical Chemistry", John Wiley and Sons, New York, 1971, pp. 287-8. 2Baxter, D., and Huber, C., J. CHEM. EDUC., 49, 535 (1972).
Preparation and Application of Carrier-Free 212Pb in a Radiochemical Teaching Laboratory
E. Broda T. Schonfeld Institute of Physical Chemistry and Institute of Inorganic Chemistry University of Vienna A-1090 Vienna, Austria Kvale and Skarestad have, under the above heading, described a simple and cheap method for the production of radioactive lead (212Pb).'They use a thin layer of solid Z28Th nitrate as the thoron generator. May we point out that the same isotope of lead can be obtained even more simply and cheaply by drawing a current of air through a solution of natural thorium nitrate and absorbing the thoron in water. This can be accomplished using two wash bottles in series, with filter fibres inserted in between to hold back dronlets of the thorium solution.2 When applying this method, no radionuclides-such as separated 228Th-need be purchased a t all. Only a small stock of natural thorium nitrate is required.
,...-., 'KvBle, E., and Skarestad, M., J. CHEM. EDUC., 51,756 (IY'i41.
2Broda, E., Fabitschowitz, H., and SchGnfeld, T., Monatsh. Chem., 83,482 (1952).
A Teaching Analogy to Catalyze Understanding of Energy-Rich Organic Phosphates Robert E. Kuttner Department of Physiology Louisiana State Unversity Medical Center New Orleans, 70112 The concept of the metabolic utilization and storage of energy-rich organic phosphates is sometimes difficult to convey to nonchemistry majors in short or elementary hioVolume 54, Number 9, September 1977 1 577
chemistry courses. A useful device is to illustrate the stmcture of trinitroglycerine along with that of 1,3-diphosphoglycerate, a hieh enerw comoound formed durinr the breakdown of a resemblance bein t& body: Students readily tween the molecules. The reoutation of nitroglvcerine for explosively "producing" eneigy is common knowledge. A comment that both nitrogen and ~hosphomsare in the same column of the Periodic ~ k h l and e havk chemical similarities is usuilllv sutlicient tn convince skepticd listeners that organic are capahle of storing and releasing metabolic energy. I t is necessary to emphasize that only the anhydride phosphate bond containing compounds &e energy-rich; otherwise students will incorrectly expect various hexose and triose phosphates in the glycolytic pathway to he high-energy molecules. Once the concept of high-energy phosphate has been imparted by the parallel between organic nitrates and phosphates, reference to an accepted explanation for this biochemical property is appropriate. A good follow-up uses total possible resonance forms as outlined and argued by Oesper (Arch. Biochem., 27,255 (1950)).
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An Organic Lab Practical in Library Resources J o h n F. Rosen and Deborah Meeder Nycz Broward Community College Pompano Beach, Florida 33063 We have designed an exercise which gives students experience in the utilization of various resources that wouldordinarily be found on reserve in our library. Students are required to include information in their lab write-ups regarding the physical constants of all of their reactants, reagents and products, and usually do not rely on these resources beyond the table of physical constants. For this reason, we designed our lab practical so that the students would gain greater appreciation of the myriad of information contained in the resources. Each student was given a list of five questions, selected from a hnnk of 120 questions, and a handout descrihing the types
578 I Journal of Chemical Education
of information contained in the references thev would beusine to answer the questionn. The references used were "Lange's Handbook of Chemistw." "The Handbook of Chemistrv and Physics," "The ~ e r c k i n d e x , ""The Condensed ~ h e k c a l Dictionarv." and the "Aldrich Cataloeue." The questions are varied and deal &h topics which range from the correct method of disoosal of an organic comoound to the analytical composition i f a food prod&t. ~om'of the auestions are humorous due to their obscuritv, and provide challenge to the students in their search. ~ s a m p f set e of questions follows
a
In what form does one purchase see-hutyllithium and what is the proper method of its disposal? What is the dissociation constant for novocaine? What is the maximum allowable concentration of zinc in drinking water? What is the diamagneticsusceptibility of coronene? What is the half-lifeof ZBMg? This practical has been presented to students during a lab class. The resources are nresent and availahle for student use while they are waiting for a particular reaction to reflux, distill ur cool down. This fills ur, what mirht otherwise be ronsidered free time and allows f& interes&ng exchange between students. Reaclion to this practical has been favorable and students are renerallv amazed at the diversity of information contained in &e reso&es. The list of questions is available upon request.
Compact Compact Gregory V. Nelson of Drew University in Madison, New Jersey points out that an instructive model showing the rigidity of the helical folding pattern and the flexibility of a non-helical region in a protein can be constructed from a cardboard mailing tube. At the center of the length of the tube, carefully cut along the helical seam for about one revolution. Simply twist the two ends of the tube to unfold the helix and to bend the remaining helical regions back toward each other. For demonstration purposes, have also an intact mailing tube a t hand to show the original rigidity.
