In the Classroom
The Crystallization Clinic—A TA Orientation Exercise Marjorie Kandel Department of Chemistry, State University of New York at Stony Brook, Stony Brook, NY 11794-3400
As Coordinator of Undergraduate Organic Laboratories, each year I work with a group of about 16 TAs. Although a few are returning graduate students, most are undergraduates and beginning graduates. The Crystallization Clinic is our orientation exercise. While practicing this key technique, TAs also become familiar with the location of supplies and equipment in the laboratory and the contents of their students’ kits. After a demonstration by our “guest expert” (a volunteer professor), TAs participate in a contest with the following rules. • • •
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Select one of the different 500-mg solid samples available. These will not be identified by chemical name. Find a suitable solvent. Recrystallize your sample. Perform a hot filtration if there are insoluble impurities. Perform a Norit treatment if there are soluble colored impurities. Leave your sample to dry. Products will be judged by the students taking the undergraduate organic lab courses. The single criterion is beauty. The winning product will be displayed with the name of the contestant, who will receive a unique prize.
Good technique is important: for example, slow cooling produces larger crystals. But there is no denying the contribution of factors beyond a person’s control—the identity of the compound, its initial purity, its behavior in the solvent chosen. And beauty is in the eye of the beholder. One of the compounds available for choice is benzil; some years the judges fall in love with its soft yellow color and award it first place.
Thus, because everyone is working with a different compound, the playing field is not level, and the contest does not really serve to identify the person with the best technique. Once we reassure our TAs that this is not our goal, they relax and have fun, exchanging good-natured challenges as they each strive to win. The Clinic serves to review recrystallization, as we will teach the technique, for participants with varied educational backgrounds. It serves to orient the TAs in the lab layout. Through the frustrations and successes of a shared activity, it helps to form group spirit. It can, by reminding TAs of their own first experience in organic lab, give them empathy with the students they will be teaching. In the undergraduate class, before the judging, the instructor can discuss properties that are desirable in organic crystals. There is a place for esthetics. I tell my students, “If you love making beautiful crystals, this may be a sign that you should become an organic chemist!” Common compounds that work well are acetanilide (mp 113–115 °C1), benzanilide (164–166°), benzhydrol (65–67°), benzil (94–95°), cholesterol (148–150°), fluorene (114– 116°), phthalonitrile (139–141°), salicylic acid (158–160°), and triphenylmethane (92–94°). It is evident that some of these melt on the steam bath; care must be taken to avoid oiling out. The prize, much coveted, is a trophy made in our departmental glass shop. Note 1. All melting point values are from the Aldrich Catalog Handbook of Fine Chemicals, 1996–1997.
JChemEd.chem.wisc.edu • Vol. 76 No. 1 January 1999 • Journal of Chemical Education
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