In the Laboratory
An Introductory Organic Lab for the Problem-Solving Lab Approach
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Edward G. Neeland* Department of Chemistry, Okanagan University-College, Kelowna, BC V1V 1V7, Canada
Chemistry instructors acknowledge that standard lab experiments in chemistry do not challenge students to think independently (1). This is not unexpected, because the experiments are often given in a format that allows completion without too much thinking or preparation. Simply put, students follow chemistry lab procedures like recipes in a cookbook. Last year, this point was forcefully driven home to us when one student could not assemble a simple distillation apparatus even after attending two terms of weekly organic chemistry labs! Clearly, our approach to teaching the labs was letting some students down. In an effort to remedy this situation, some chemistry instructors have reported better results using a problem-solving lab (PSL) approach (2). We too were unsatisfied with the recipe approach and decided to convert our entire second-year organic chemistry lab program to a PSL format adapted from Browne (2). We wish to report on the success of the PSL approach in our second-year organic labs and present an introductory organic lab created to overcome some of the students’ anticipated nervousness about the PSL approach and build their confidence in the PSL method. The lab is available on JCE Online. W Skeleton of a Problem-Solving Lab Each PSL write-up begins with a clear statement of the intent of the entire lab stated in a few sentences. The remainder is divided into two parts: prelab responsibilities and experimental. The prelab responsibilities of the student are to (i) read about lab techniques specifically used for that lab section (3), (ii) view videos1 in the library that demonstrate the lab techniques, and (iii) complete the prelab questions. The prelab questions are an important part of preparing for the lab, because they have been designed to point out and, we hope, eliminate frequently encountered problems. The second part of the write-up concerns the experimental procedure. Here all available materials to complete the lab are listed, including glassware, chemicals, and instrumentation. A specific objective for the experimental part is then given and hints are provided to guide students in writing their own experimental procedure, which, when followed, would complete the lab. Over the term, the PSL’s are designed to contain progressively less information. In this way, students become responsible for remembering previous lab techniques and procedures. The final lab in our PSL sequence takes up, in its
W Supplementary materials for this article are available on JCE Online at http://jchemed.chem.wisc.edu/Journal/issues/1999/ Feb/abs230.html.
*Email:
[email protected].
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entirety, only one half of a page. In this final lab, students are required to calculate the stoichiometric amounts required of the reagents and decide on glassware, reaction times, workup, and purification methods. The First 30 Minutes of the Lab At the start of each lab, the instructors check that the prelab responsibilities of each student have been completed. These include tabulating physical properties and hazards of reagents and products, answering the prelab questions, and having a rough experimental procedure in hand. The prelab questions and experimental procedure are not marked for accuracy but instead are checked for an honest attempt. If students have not made the effort to fulfill their prelab responsibilities, they are asked to leave the lab and return when they have prepared properly. Next the students get together in work groups of 4 or 6 individuals. The work group is a brainstorming session where students blend their individual plans into one common lab procedure for that group.2 It is certainly a pleasure to listen to the students arguing the merits of one approach over another; it was evident that they had done their homework, understood what they wanted to do, and were willing to defend their plan of attack. When the final plan is drafted (in about 15–20 minutes), one student is chosen to relate the group’s plan to an instructor. This is an opportunity to test the student’s understanding in a very friendly exchange. A typical conversation might go like this: STUDENT: Well, you start the lab by putting 2 grams of your reagent in a flask. INSTRUCTOR : What type of flask? STUDENT: Oh. A round-bottom flask? INSTRUCTOR : That’s a good choice. What size should it be? STUDENT: I hadn’t thought about that. Maybe 50 mL? INSTRUCTOR : Yes I think that will work. STUDENT: Then we need to heat the reaction. INSTRUCTOR : What will you use for your heat source? STUDENT: Probably either a hot-plate or a heating mantle. I think a heating mantle would work best. INSTRUCTOR : OK, good!
The student takes us through the group’s entire plan while we listen and make constructive suggestions; then we let each member of the group try the group plan.3 There are often several different lab proposals put forth by the individual groups; we accept all procedures that will complete the lab. We stress that the students’ procedures are theirs and that there is no single “right way” to complete the lab.
Journal of Chemical Education • Vol. 76 No. 2 February 1999 • JChemEd.chem.wisc.edu
In the Laboratory
The Introductory Lab
Conclusion
We realized that this change to PSL could be very intimidating to the students and decided to create an introductory lab that would show them the method behind the problem-solving approach in a nonthreatening way. This introductory lab eventually took the form of isolating and purifying an organic solid from a mixture of sand, an etherinsoluble packing polymer, and an organic solid contaminated with an impurity. The lab was divided into three sections, each section dealing with one problem that was to be solved. The first section asked the students to physically separate the sand, polymer, and organic unknown into three beakers (4 ). We used a mixture of substances containing two familiar materials (sand and polymer) and one “chemical” (the organic unknown), thereby allowing the students to devise a simple separation and so build their confidence. They experienced no difficulty with this step and they clearly enjoyed devising various ways of accomplishing the separation. Most students began by adding ether to the mixture to dissolve the organic unknown followed by isolating the solution. This was accomplished in a variety of ways. Some filtered the solution using filter paper and funnel; others used a Pasteur pipet and cotton ball; still others simply decanted the solution. Even at this early stage of a simple step, we were pleased to see the students’ creativity. At this point, their initial nervousness was gradually being replaced by an attitude of “I can do this.” The final two sections, which involved identification and purification of the organic unknown, were then completed with confidence. This two-period laboratory introduces the concepts of differing solubilities, filtration, separatory funnel extraction, drying agents, thin layer chromatography, rotoevaporation, recrystallization, and mixed melting points. No serious difficulties were encountered by the students in completing the lab. We recommend it as a good primer lab for the PSL format or to anyone who wants a “good thinking lab”.
Our experience in converting our traditional recipe-style organic labs to a problem-solving format has been very successful.4 The students are excited about the control that they have over their experiments and we can see the development of better-thinking students who are more confident in the lab. They are gradually being forced (although they don’t realize it) to remember techniques because they are deciding when and where a technique is needed. At the end of the year, several students mentioned that, in retrospect, the labs contained too many hints. They wanted fewer hints on how to carry out the labs. Only confident students would make such a statement. We are currently converting the upper division organic labs to a PSL format.
Student and Instructor Response The PSL approach to second-year organic chemistry has worked extremely well. Students enjoy being in control of the procedure that they follow. One student who was repeating the lab section of the course was emphatic that the new PSL approach forced her to learn the material much better than traditional methods. Some student groups have devised better ways of completing a lab than we had at first envisioned. An instructor mentioned that for the first time in her experience, no one had asked which layer in the separatory funnel was ether and which was water: the students actually knew. The success of this venture has stimulated other instructors here to begin changing their labs over to a PSL format.
Acknowledgment We thank Lois Browne of the University of Alberta, who has freely shared her PSL approach and lab technique videos with us. Notes 1. Further information on the videos is available from JCE Software. See: Browne, L. M.; Auclair, K. Techniques in Organic Chemistry, Part 1, J. Chem. Educ. 1998, 75, 383; Browne, L. M.; Auclair, K. Techniques in Organic Chemistry, Part 2, J. Chem. Educ. 1998, 75, 1055. 2. If possible, we encourage students to blend their individual plans before they enter the laboratory. 3. Some of our labs require the students to work in pairs. 4. Student evaluations showed that the PSL format was found to be more challenging but taught them better than cookbook procedures. Lab instructors agreed with that response.
Literature Cited 1. Kalsi, P. S. J. Chem. Educ. 1976, 53, 553. Wiseman, F. L. J. Chem. Educ. 1979, 56, 233. Abraham, M. P. J. Res. Sci. Teach. 1982, 19, 155. Pickering, M. J. Chem. Educ. 1984, 61, 861. Broniec, R. J. Chem. Educ. 1987, 64, 961. Cooley, J. H. J. Chem. Educ. 1991, 68, 503. Mahaffy, P. G.; Newman, K. E.; Bestman, H. D. J. Chem. Educ. 1993, 70, 76.) Klemm, W. R. J. Vet. Med. Educ. Educ. 1994, 21, 2. Ege, S. N.; Coppola, B. P.; Lawton, R. G. J. Chem. Educ. 1997, 74, 74 and references therein. 2. Wilson, H. J. Chem. Educ. 1987, 64, 895. 3. Zubrick, J. W. The Organic Chem Lab Survival Manual, 3rd ed.; Wiley: New York, 1992. 4. Other educators have chosen to separate mixtures of organic unknowns using chemical reactivities: Toong, Y. C. J. Chem. Educ. 1996, 73, 476. Leonard, J. E. J. Chem. Educ. 1981, 58, 1022. Laughton, P. M. J. Chem. Educ. 1960, 37, 133.
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