adltad by WALTER A. WOLF Eisenhower College Seneca Falls. New York 13148
An Improved Method in the Redox Titration of Oxalic Acid by Permanganate M. Datta, Snresh C. Ameta, P. N. Pande, H. L. Gupta, and M. M. Bokadia School of Studies in Chemistry Vikram University, UJJAIN(M.P.) 456010, INDIA The oxidation of oxalic acid bv acid ~ermannanatehas been studied for more than a century, and while the mechanism of the reaction is still obscure. the stoichiometry is well established. Hence, i t is used as avolumetric exercfse for intermediate classes. It is necessary to heat the oxalic acid solution to about 60-7O0C; otherwise-the cold solution may take about 10 min to decolorize even a drop of permanganate. T o avoid heating, or in other words, to save fuel, the authors have induced this reaction with ascorbic acid. In a typical experiment, 0.05 M KMn04was used to titrate M ascorbic 0.05 M oxalic acid. One-half milliliter of 1.0 X acid and 6 ml of 5 N sulfuric acid were added to the oxalic acid solution before titration. It was observed that titration could be completed w~thina reasonable time cumpilred to the tit r a h n carr~edout with heating. The results are effected by less than 0.5?.an allowable error in intermed~atrclasses.
Optical Illusions in Drawings of Cyclohexane Derivatives Martin R. Feldman Howard Uniuersity Washington, D.C. 20059 The discussion of conformations of cyclohexane derivatives in the introductory organic course often includes optical isomerism. A typical exercise or exam question asks for the relationship between various structures, such as 1-111.
Are thev enantiomers. diastereomers. or identical? For the structures shown, it iseasily seen that they are all cis disubstituted and therefore are not diastereomers. Further, I and I1 are mirror images and cannot be superposed (in I, X is "in the back;" in 11, X is "in the front") and thus are enantiomers. It is obvious that 111is an "upside down"version of I or 11. If one rotates I11 around the indicated axis, it is apparent that I11 is identical to 11. On the other hand, if one turns the page upside down, 111 appears to he identical to I! The paradox results.-from ontical illusion in the re~resentationof chair - - - ~ an cyclohexanes. The upper horizontal line,in the ring is away from the observer ("in the hack"). T u r n ~ n gthe page upside down not only reverses groups in an upldown fashion, but also A~
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reverses "hack" and "front", as the upper horizontal line (back) becomes the lower one (front). Although warnings about the proper handling of Fischer projections are common, I have not previously seen a warning about improper viewing of cyclohexanes. The paradox described here was brought to my attention by my students, most forcefully by Mr. Charles Thomas.
Undergraduate Research Originating from Answers to Examination Questions A. G. Pinkus Baylor University Waeo, TX 76703 Although a number of articles have appeared (1-9) in which various ways of introducing research to undergraduates are discussed, opportunities for research are mainly directed toward chemistry majors. Generally only a small percentage of undergraduate students (chemistry majors or nonmajors) taking chemistry courses participate in research. In fact, very few constructive suggestions have heen made on this topic. Wilson (10) has discussed a research approach in the introductory laboratory involving preparation of some inorganic complexes, their analyses, and problems evolvingfrom these experiments. Another approach toward a research-oriented general chemistry laboratory has been discussed by Venkatachelam and Rudolph (11). This paper gives the results of a novel approach to involving undergraduates in research projects which stem from their original ideas. Although the experiment was carried out with a sophomore level organic chemistry laboratory class, it is also applicable to freshmen level and other undergraduate lahoratory courses. Practicallv evervone engaged in teaching undergraduate courses at the und&graduagbeginning chemistry organic chemistry levels has encountered interesting and/or imaginative answers during the course of grading &aminations.ln planning for the teaching experiment conducted, a list of such answers collected from examination papers was made. During the latter part of the second semester lahoratory part of the course (at a time when the students had learned some laboratory techniques) the students were told that they were to participate in an experiment in which they were to try out some of the unusual reactions and syntheses they had sugeested in their answers to examination questions durinn the the list WRS made &nurse. A selection of experiments h s e d on feasibility, availability of chemicals nnd equipment. avoidance of toxi; chemicals,and possibly dangerous reactions. The projects to be investigated were assigned as much as possible to students who originated the ideas. Since some studentsdid not suggest ideas whereas some suggested more than one, suggestions were distributed to the former from the "idea pool" which also included ideas which evolved from those available. Thus, for example, the same reaction could be carried out udder various conditions (temperatures, solvents, order of addition of reagents, etc.). The students were Volume 56. Number 10, October 1979 / 659
