ditd by:
WALTER A. WOLF C d g d s Univenity Homibn, New York
Theoretical Shape of Acid-Base Titration Curves without Using Logarithms Mary S. Vennos Essex Community College Baltimore County, Maryland 21237 We have e large number of students in paramedical programs taking the equivalent of a one semester course in general chemistry whose mathematical backgrounds usually do not include logarithms. Thus any rigorous calculations to obtain the theoretical shape of a titration curve would be pointless. However, I have found that they are able to follow an approximate approach as outlined below. Assuming that we begin with 100 ml of 0.100 M HCI @H = 1.0) and titrate with, 10.0 M NaOH, the small amounts of NaOH solution added during the titration make a negligible difference to the total volume so that we can easily calculate the p H after the addition of the following specific volumes of the 10.0 M NaOH, without using logarithms
Vol. NaOH 0.00 0.90 0.99 L03 LO1 1.10 2.04 (ml) pH
LO
20
3.0 7.0 ILO 120 13.0
Similar calculations can be made starting with 100 ml of a 0.100 M solution of an imaginary weak acid with a K, of 10-9 Again the titration is assumed to be done using 10.0 M NaOH. Without using logarithms i t is easy to calculate the pH a t the equivalence point (9.0) and a t specific stages of the titration. The results are as follows Vol. NaOH 0.00 0.90 0.99 LOO LO1 1.10 2.00 (ml) pH 3.00 3 5 4.0 9.0 11.0 120 El0
I would he glad lo send anyone who is interestrd a cups of the derailed presmtntinn given to studrnti including the tirratlon L U ~ W Sas plol!ed from I ~ C S C .approximatecalculatiuni.
An Interesting and Successful Organic Experiment Benjamin J-S Wang Trenton State College Trenton, New Jersey 08625 We have found that students in our first-year organic chemistry classes were very enthused about the synthesis of the popular commercial compound, N.N-diethyltoluamide, an active ingredient in the insect repellant "OFF." In the course of the synthesis (one 3-hr laboratory period) the students acquire some important techniques in handling reactive reagents and the use af chromatographic separations. The yield of the reaction is good (70%) and the students found it to be a great treat when they were able t o use a product prepared by their own hands. Place 2.8 g of m-toluic acid (Eastman technical grade, recrystallized twice from 50% aqueous acetone) and 3 ml of thionyl chloride in a 250-ml Erlenmeyer flask fitted with a ane-hale rubber stopper. A gas trap is set up by connecting one end of a 2-ft rubber tubing to the stopper and the other end into a beaker containing water. After adding a few bailing chips, the mixture is
Editor's Note: Due to the constantly greater disparity between available space and the amount of material suhmitted for publication, this Journal has initiated a column of brief announcements. These will consist of succinct statements of the key ideas of the authors along with the possibility of obtaining further material related to the subject upon request. The types of articles appropriate for this feature include improvements on well-known teaching methods or experiments, simple new experiments, computer programs, new techniques or methods that would appeal to a limited section of the audience and speculative articles on educational methods and philosophy. Authors who wish t o submit articles far consideration for publication should send the manuscripts (one double-spaced, typewritten page) and the supporting materials t o Dr. Walter A. Wolf, Editor, Chem Ed Compacts, Department of Chemistry, Colgate University, Hamilton, New York 13346. heated gently with a flame until bubbling almost ceases (about 3-5 m i d . Remove the tubing from the water, then stop the heating. Allow the flask to cool, add 50 ml of dry ether and then, (dropwise a t first) 20 ml of ether solution containing 7 ml diethylamine. At the end of the addition, the mixture is washed sneeessively with 20-ml portions of 10% NaOH and 3 N HCI, dried over magnesium sulfate and evaporated to about 5 ml volume. The brown liquid is purified by eluting with petroleum ether from a chromatographic column packed with 15 g alumina in petroleum ether. N,N-diethyltoluamide will be the first compound to exit. Evaporation of petroleum ether yields 3-3.5 g of pure colorless amide.
Multiparameter Nonlinear Optimization and Least-Squares Data Reduction on Hewlett Packard Desk Calculator Systems Julius G . Becsey Aerospace Research Laboratories (ARL) Chemistry Research Laboratory (LJ) Wright-PattersonAFB, Ohio45433 ~ a G eL. l Bartelheimer Systems Research Laboratories Dayton, Ohio 45440 Nonlinear least-squares data analysis is a widely used computational method in chemical data reduction. There has been a sizable body of literature, published in this Journal, for nonlinear data reduction (2-51 and optimization for various chemical calculations (6, 7). However, all described methods require the use of computers or some additional calculatianal aids such as graphs or plats. The present report makes available a desk calculator program, based on an algorithm in reference (31, for multiparameter nonlinear optimization and least-squares data reduction on pragrammable Hewlett-Packard desk calculator systems: The HP 9100A or B with extended memory and the H P 9820 with 429 internal registers. The program can be used in the following modes: 1) to search for local minima of any function S(a, b) with one ( a only) or two (a and b) nonlinear variables, with or without constraints; 2) to reduce data sets, xi, yr, by the method of least-squares into their nonlinear functional representations: (a) yi = AX! Volume51. Number 10. October 1974
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