E. 1. Wehry'
lndiana University Bloomington, Indiana 47401
"Open-Ended" Experiments for Undergraduate Analytical Chemistry
The desirability of providing opportunities for independent investigation by students in nndergraduate laboratory courses has become widely recognized. I n the area of analytical chemistry, such "openendcd" experimental work is especially desirable in terms of providing orientation to the analytical approach in problem solving. We have developed and utilized a series of twentyfive research-oriented experiments in our junior-level introductory course in analytical chemistry (for which one semester of physical .chemistry is- prerequisite). The course includes as students both professional chemistry majors and prc-medical students with concentration in chemistry; a. wide spectrum of interests, attitudes, and abilities is represented. Enrollments are normally on the order of fifty students per semester; laboratory sections generally consist of twelve students and one gradnate assistant. The laboratory associated with the course begins ~ v i t ha series of rathcr conventional experiments, in which detailed procedures are supplied to the students. As the semester proceeds, information is gradually and select,ively deprived from the students in succeeding experiments; the students' independence slowly increases. By within six weeks of the end of the semester, it is feasible to assign to each student a minor, carefully selected, research problem with some confidence that he will be able to make significant progress with a minimum of explicit direction. Accordingly, fdr the student's final experiment in the course, he is expectcd to perform an experiment in which essentially no specific directions are provided. A general statement of a problem is provided; in some cases, hints regarding the proper mcthod of attack are given. In general, the student is on his o m , though he is encouraged to consult vith the instructor and graduate assistants and to make use of the library. The statements of the experiments are sufficiently brief that a complete compilation of the 25 problems comprises less than five typed pages. Five to six weeks is allotted for performance of an open-ended experiment. Each student is required to submit a written report at the end of the semester. Primary factors in the evaluation of this report include the thoroughness with which the student has researchcd his problem in the library, the nature of his experimental approach, the quality of his results, and (most important) the care and thoughtfulness (or lack thereof) with which the student has interpreted his findings, including an assessment of the reliahility of his cxperimental data.
' Present address: Chemistry Department, University of Tennessee, Knoxville, Tenn. 37916.
This experimental approach imposes severe demands upon the graduate assistants; in any given laboratory section, as many as ten different experiments will simultaneously be in progress. Such a teaching assignment is, of course, educationally valuable to a graduate student in analytical chemistry. It is, however, obvious that teaching assistants for such a course must be chosen with considerable care. Criteria relevant to design of open-ended experiments include the following (a) The scope of the experiment should be sufficiently broad that the student has s, variety of options in his method of attack. The experiments should be non-routine, yet sufficiently facile that Droxress in a short a dilicent undergraduate can make a~preciable .. . period of time. ( b ) Due to the number of students in our course, the exoeriments must rely upon relatively simple instrumentat&. ~ence, our set of 25 experiments requires the use of only pH meters, absorption spectrophotometers (in most, but not all, cases Bpectronic 20's are sulkient), conlometers, and polarographs. Of course, no unusual safety hazards should be encountered in any of the projects. (c) Particularly in an experiment which involves performance of a quantitative determination, there shonld be sources of error which are not trivial,. vet " which can be aooreeiated and controlled by an alert student. ( d ) Finally, whenever possible an experiment should be related to a "real" problem. ~~
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For a large, diverse student body, it is necessary to have available a variety of experiments. Consequently, our problems range from fundamental studies of equilibria and kinetics in solution to the analyses of specific commercial products. Virtually any student should be able to find within this list an experiment of some inkrest to him. Responses of students to this form of laboratory exercise have been usually favorable and often enthusiastic. We provide below a sampling of eight representative open-ended experiments currently utilized in our course; the problems are reproduced in their entirely as presented to the students. The literature references cited are not provided to the students. 1) The olefin content of hydrocarbon samples can he determined hy bromination, carried out either chemically or coulomet. rically. Develop chemical and coulometric bromination procedures for the determination of cyclohexene in the presence of cyclohexsne, and apply the method to some actual samples, including a t least one "unknown" supplied by the laboratory assistant. Evaluate the accuracy, sensitivity, and precision of each method; compare the two methods critically. (Note: these methods are widely used in analysis of t,race olefins in petroleum samples.) 2 ) Determine the solubility product of lead sorbate (the lead salt of sorhic acid) in the solvents methanol and isooctane. The lead sorbate asample will be provided by the Ishamtory assistant. Investigate carefully the effect of "inert" electrolytes upon the solubility of this salt in methanol. How do the electrolyte effects compnremith those you would anticipate for aqueousmedis? 3) The interaction of aromatic compounds wit,h standard styrene-diving1 henaene ion-exehange resins is often very strong. 111 Volume 47, Number 12, December 1970
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fact, such r ~ i n can r be used as stationary phases for the chromatographic separation of mixtures of neutral phenols. Estsblish condition5 under which mixturs containing three to five phenols cnn be resolved via. this approach. Study the influence of relevant column operating parameters upon the separation efficiency. What can you say about the interactions between phenols and ion-exchange resins which are responsible for the observed separation^?^ 4) Oxidationof the dye malachitegreen is catalyzed by Mn(I1). This o~talvsiscan serve as the basis for a kinetic method for determination of Mn(I1). Design such a method; investigate its accuracy, precision, and sensitivity; itnd examine the influence af plausible interferences." 5) Glucose in nqueous solution can be determined by measuring the rate of its oxidation to glueonic acid, as catalyzed by the enzyme glucose oxidase glucose
+ On + H.0
---------+Hz02 + gluconic acid gluoose oridase
This reaction is most conveniently followed by coupling the production of HIOl to a second, much faster, enzyme-catalyzed reaction which consumes the H202itnd produces a colored product. Evaluati the precision and sensitivity of this method, and the influence of the presence of (a) other sugars and ( b ) reducing agents. I n the process of performing this experiment, determine the glucose content of an unknown supplied by the assistant. From your study of this method, comment on its applicability to the determination of glucose in blood samples. 6) The rate of the redox reaction between pemulfate ion and iodide is given by
The products of the reaction are sulfate and IJ-.
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Journal of Chemical Education
Determine k,
m, and n, end discuss possible mechanisms far the reaction."
7) The ethylene glycol content of commercial antifreeze Samn l s can be determined bv s n oxidation-reduction titration. Any number of other techniqies can also be applied to this analysis. Devise two procedures, one of which involves s. redox titration, and "test" them on synthetic samples of ethylene glycol. Then apply each method to the determination of ethylene glycol content of three different commercial antifreezes. Campsre the two methods critically. 8) I n methanol solution, Agf reacts with equimolar mixtures of m- and p-phenylenedismine to produce a colored dye; the reaction is an oxidative-coupling process anslogous to those used in some color photographic films. Determine the stoichiometry of the reaction and evsluate its utility as an analytical method for determination of Agt. Study the effect of plausible interfer-
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The entire set of experiments, including the specific "ground rules" applied in our course, can be obtained upon request from the author. Acknowledgment
Valuable assistance in testing a number of the experiments was contributed by J. W. Atair, R. A. Leese, and S. Sundararajan. *SEKI,T., J . Chromatog., 4, 6 (1960). S. L.. Anal. 3 F ~ ~A. ~A,. ~SOBEL. ~ . C.. ~ . AND ~ zJACOIIS. . Chnn., 35, 1721'(1963).' ' WILMARTH,W. K., AND HAIM,A,, in "Peroxide Reaction J. O.), Interscience (division of Mechanisms" (Editor: EDWARDS, John Wiley & Sons, Inc.), New Yark, 1962, p. 175. " E B E ~ ~ S , R. L., A N D LEVIN,V., Anal. Chem., 40, 2053 (1968).
