edllad by
WALTER A. WOLF
Calculators in Freshman Chemistry-An Alternative View
Eisenhower College Seneca Falls, New Yark 13148
A Topical Alkene Preparation and Oxidation Marvin Gold California State University, Chico Chico, CA 95929 Much has been written in this Journal [52, A346 (1975);54, 177,225,628 (1977)l about the benefits of the widespread use of calculators in freshman chemistry. The purpoie of this communication is to suggest that there is also a serious negative aspect of such use and that perhaps teachers need to strike an appropriate balance between the "good" and the "had." The past several years have convinced me that a diiproportionately large number of students enrolled in the science majors freshman chemistry course are seriously deficient in many arithmetic skills. Beyond this, I have observed a general difficulty in performing those tasks which are nourished by a background of practice in mental arithmetic. I am referring here to the ability to make "hallpark estimates," to recognize an unreasonable calculated quantity, or to recognize, intuitively, the insignificance of most of the digits in the 8-place calculator output of typical calculations. I believe that these skills derive, a t least in part, from practice in using numbers and that such skills are blunted when reliance is transferred from brain to calculators. Given the problem, what should be done? About a year ago I reached a decision to place some restrictions on calculator use in the hope of increasing brain usage. The restriction I have adopted is one of not permittine calculators to be used on hour examinations. ~ u m e r i c adata l is presented in such fashion that only the basic math skills are needed for problem solving. Since this is not a popular thing to do, I make a special effort (including a "letter" to all students) to explain my concern for their education and to emphasize to them that their professor is not simply an old-fashioned, anti-calculator, "slide rule nut" who is still livine in the dark aees. Students are urged to bring their calculat&s to the lab, wThere they can gain proficiency in their use. The discovery that H+ concentration can he obtained from pH without an inverse log capability-using the vX key-is an excellent lesson to the student that a caculat& cannot replace a solid understanding of mathematical operations. Feedback from students indicates that, while initial reaction to this policy tends to be one of dismay (even fear), this eventually gives way to the feeling (by a 2-1 margin) that such a policy is beneficial, or a t least not a hardship. This feedback comes from written anonymous evaluations obtained at the end of each semester. Judeine .. .. from conversations with colleaeues. .. . and from cmnments in this .Journnl, 1am not alone in my concern over the current level of tnnth skills of a d e r e freshmen. I ha\.? tried to deal with it in my way. What is way? This column is devoted to brief announcements of new ideas in chemical education. These consist of succinct statements of the kev
manuscripts (one double-spaced, typewritten page) and the supporting materials to Dr. Walter A. Wolf, Editor, Chem Ed Compacts, Department of Chemistry, Colgate Univenity, Hamilton, New York 13346
526 1 Journal of Chemical Education
Reginald H. Mitchell Blaine F. Hawkins a n d Paul R. West University of Victoria Victoria, B.C. V8W 2Y2 Canada For the first preparative experiment of the introductory organic laboratory we have developed an experiment to demonstrate various aspects of alkene chemistry that is interesting to students and somewhat unusual. Basically the experiment consists of thermally depolymerizing polystyrene to styrene (i.e., by simulated conditions that exist in a fire), followed by an investigation of the properties of the flammable monomer ~roduced.Students are asked tocomparemd commrut on (he tlammahilities of the liquid styrene they ohtain and of the polvsrvrene they used he students are able to record ir spictra of their monomer and compare it to the polystyrene calibration film provided with most spectrometers. The C=C is immediately apparent and can be confirmed chemically. The inertness of the benzene rine is then emnhasized in the exneriment that follows-an uxidatiun with potassium p(nnanganntv. Ilist~ricalls.vermimeanilte ion is aidelv used in teachinn beginning organic chemistry because it readily oxidizes a variety of compounds. In reality, however, its application is more limited, especially for hydrocarbon oxidations, because of its low solubility in most non-polar solvents. The recent interest in use [J. CHEM. EDUC., 55,350 and 429 (1978)l and wide availability of phase transfer agents has thus led us to modernize our approach to such oxidations..We allow half the class to oxidize styrene with potassium permanganate in CHzC12-Hz0-CHaCOOHmixture at room temperature in the presence of ADOGEN 464 ( a cheap, commercially available (ALDRICH) methyltrialkyl (CBC,~) ammonium chloride) to form the easily isolated benzoic acid. They are asked to compare their results (usually twice the yield) with the other half of the class that use the more traditional and drastic alkaline reflux conditions. Experimental details are available upon request.
The Physically Meaningful Solution o'f the Quadratic Equation Me1 Levy Larry D. Byers Tulane University New Orleans, LA 70118 .Many. quantitative problems in chemistry. require solving . . a quadratic equation: a i a br c = 0. The common situation in which such a ~ r o b l e moccurs is an acid dissociation where x represents th;concentration of a chemical species at equilibrium. Unless the roots are degenerate, there will he two values of x which satisfy the equation, thus potentially presenting some ambiguity. I t is our purpose to show that the
+ +
potential ambiguity (i.e., two unequal but physically meaningful roots) never arises. When an acid, HA, is dissolved in water, the concentration of A- a t equilibrium can he obtained from the definition of K,:
Further, if HA is the only source df H+ and A-, then (1) [A-I.,' + Ka [A-leq - K,, lH.410 = 0 where [HA10is the initial concentration of the acid. Wemust prove that (1) the quadratic equation always yields a value of [A-I,, such that 0 < [A-Ieq < [HAIo;and (2) of the two roots of the auadratic eauation.. onlv . one satisfies the above inequality. Proof: The solutions of eqn. (1) are
[A-I,
But, KO
=
-K, i d K G Z+ 4Ko[HA10 2
(2)
+ 4K0[HA10 < (Ka + 2[HA]o)2.So, it follows that d K a P+ dK.[HA]a
< K,
+ 2[HA]o
(3)
Substitution of eqn. (3) into eqn. (2), and utilization of 4K, [HA10 > 0, yields: 0 < [A-I,,
< [HA10
for that solution of eqn. (2) which corresponds to the positive square root. On the other hand, the solution of eqn. (2) which corresponds to the negative square root must be a negatiue real number because both KO and {Ka2+ 4K,[HA]ol are positive. The proof is now complete.
Computer Quiz on the Periodic Table J. S. Wasson Dalhousie Uniuersity Halifax, N.S. B3H 2S7 Some asoects of the ~eriodictable are best learned bv practice which we offer students in the form of an interactive computer program PERIOD. The introductory section of PERIOD reviews general concepts such as whether rows or columns corresoond to periods. Before this introductory section a periodic t a b l e k printed but with three atomic symbols and numbers (chosen at random) missing. The student must identify each of the unknowns given only the atomic symbols. The student determines the atomic number, most stable electronic configuration, typical oxidation state, and name. The program supplies information values, some help for inappropriate responses, and additional descriptive information. The wording of the questions on the quantum numbers n and 1 was influenced by Pilar's recent article (J. CHEM. EDUC., 55, 2 (1978). The information values are calculated following Bonchev and Kamenska (Croat. Chem. Acta, 51,19 (1978). This calculation can easily he omitted. Scores on all questions are printed a t the end of the program. This Fortran program has run successfully on a CDC6400 for two years and has been submitted to the Central Program Exchange, Wulfruna St., Wolverhampton, WV1 ILY.
Volume 56. Number 8. August 1979 / 527
