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An Inexpensive Pipetting Device David Racusen Department of Microbiology and Biochemistry University of Vermont Burlington, 05401 Pipetting may he the commonest laboratory operation in hiochemistry and its safe practice deserves considerable a t tention. Common alternatives to mouth-pipetting consist of a variety of devices which are expensive, clumsy, andlor difficult to clean. The following self-made apparatus has been tested by many years of successful student use. I t is constructed from a "Koroseal" bulb (B.F. Goodrich Co.) having an internal volume of about 50 ml. The open end of the bulb is frozen in a Dry Ice solvent bath and immediately tapered, using a sharp reaming tool on a drill press. The internal taper accommodates common serological pipets from 0.1 to 25 ml. It is important to note that the large end of the pipet is held against the taper and is not pushed into the bulb. In effect, the tapered section of the bulb acts as a pair of lips. Novices have little trouble in relating the new method to mouth-pipetting.
Easily Constructed Models for Demonstrating Stereochemical Nonrigidity in Four- and SixCoordinate Complexes Robert A. Levenson Texas A&M University College Station, Texas 77843 Stereochemical nonrigidity is now a well-recognized phenomenon in transition metal chemistry (1). While some models which demonstrate intramolecular rearrangements are available, in general construction is not such a simple and straightforward task that students would be likely to build them (2). Stereomodels which are easily constructed from paper (3) are likely to he more popular. I have availahle, and will he pleased to supply upon request, templates and instructions for models easily constructed of paper which demonstrate stereochemical nonrigidity. The six-coordinate model illustrates the Bailar twist, optical activity, and intramolecular cis-trans isomerization. Interconversion hetween tetrahedral and square planar complexes may he shown with the four-coordinate model. Literature Cited (11 Muhe., J. I., J. CHEM EDUC.. 51. 94 (1971); Muetterties. E. L., Aecovnla C k m . Res, 3,266 (19701. (2) Rics, J. G., J. CHEM. EDUC., 50, 854 (1913): Rmombead, J. A., o..Yer. M.. and Meller, A , J. CHEM. EDUC.. 45.716 (19681. (3) Alexander, M. D., J. CHEM. EDUC., 50, 125 (1973): Reslaod, 8. H., and O'Brian, R. J.. J. CHEM. EDUC.,48.771 (19711.
The Paper Clip Mole-An Undergraduate Experiment T. Cassen University of Georgia Athens, Georgia 30602 Beginning students in chemistry very often do not fully appreciate the concept of the mole, and its significance with respect to a balanced chemical equation. In our course for non-science majors we employ an experiment which is designed to illustrate, in graphic terms, the concept of the mole, Avogadro's number, the law of conservation of mass, and how these concepts bear on balancing equations. In an attempt to let the student see how things work on an "atomic level" we use paper clips of different sizes to represent atoms. In essence, the average weight of each size of paper clip is determined relative to some reference mass, and represents the "atomic weight" of the paper clip. Each type of paper clip is assigned to represent a different atom, and "molecules" are constructed by attaching the appropriate paper clips together. The equivalent of Avogadro's number is then determined, using the "atomic weights" found in the first step. To demonstrate the law of conservation of mass for a given balanced chemical equation, the appropriate number of moles of reactants and products are measured by counting the required number of paper clip atoms and molecules (using the determined value of "Avogadm's number", in conjunction with the coefficients of the halanced equation), and comparing the total masses of reactants and products on a double pan balance. Unless the atomic weight scale is based upon a carefully chosen reference it is likely that "Avogadro's number" will not be a whole number of particles. While this does not necessarily invalidate the experiment, it does intmduce a certain inconvenience. For a system involving only two kinds of atoms, we have found No. 1 and No. 3 gem paper clips (0.036 inch diameter wire) suitable to represent atoms. with 6 mm hollow ~erforated elass beads (Fisher Scientific) as a reference mass. A comdete description of our experiment, with further details, may be obtained from the author.
Editor's Note: This column is devoted to brief announeements of new ideas in chemical education. These consist of succinct statements of the key ideas of the authors along with possible information an obtaining further material related to the subject upon request. Authors who wish to submit articles for consideration for publication should send the manuscripts (one double-spaced, typewritten page) and the supporting materials to Dr. Walter A. Wolf, Editor, Chem Ed Compacts, Department of Chemistry, Calgate University. Hamilton, New York 13346.
