WALTER A. WOLF

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WALTER A. WOLF Cdgate University Hamilton, New York

Simulated Student Samples GordonA. P a r k e r University of Toledo Toledo, Ohio 43606 Current emphasis on the world in which we live and our obligation to conserve its resources to the best of our ahility have awakened a new interest in the study of materials we find about us.'The student is, or should he, interested in, for example, the type and quantity of pollutants issuing from a manufacturing plant which effects the air we hreathe or knowledge of the function of various trace metals in our bodies, information necessary for helping to diagnose and treat certain diseases. Various natural substances can be used as samples for student investigation in his or her study of these and other concerns. Frequently these studies involve qualitative and quantitative analvsis of complex materials.-studies of this-type have, at some institutions. already. replaced those using. more traditional . samples to students. Samples of natural origin offer a considerable challenge to both student and instructor if accurate, meaningful analyses are to be performed. Unless one has a thorough understandine" of a particular s a m.~ l e. .including possible interfering effects of matrix components, the results obtained from determination of constituents present can he erroneous. Simulated samples are intended to aid in a student's study of a real sample. The mixtures are based upon actual standard samples taken from the literature where they were used in the study of a particular material. A student interested in studying a constituent in a certain available sample can perform his or her investigation first on the synthetic mixture. Experience is thus gained in the experimental techniques employed and better evaluation is made of matrix effects upon the results obtained. W ~ t hthis information a more meanineful intemretation of results should be possible from th;real sample for which no true answer is previousls known. Besides serving as standards for studying real samples, the simulated mixtures can themselves be used as samples especially in those situations where it would be difficult to obtain real samples. Directions for preparation of samples simulating animal tissue ash, coal ash, copper refinery flue dust, plant ash, rodent teeth ash, and soil ash are available from the author.

106

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Journal of Chemical Education

A Computer Program for the Analysis of Titration Data D. M. Seholler Lebanon Valley College Annville, PA 17003 M. L. Lyndrup Lebanon Valley College Annville, PA 17003 A computer pmgram, TITRATE, has been written for student usage in our introductory chemistry and hiochemistry courses to analyze titration data for monoprotic and dipmtic acids. The program, written in interactive BASIC, employs an algorithm which is a modification of the second derivative method of the location of an equivalence point in a titration curve for the determination of the volume of titrant added a t the equivalence point using student titration data (oH versus volume titrant added). The ~ e n d e r s o n - ~ a s s e l b a l cequation h is then used to determine the equilibrium constant(s) . . for the acid from the volume a t the equivalence point and the experimental data. The volume of titrant added a t the equivalence point has been determined to within f 0.5% and the pK,(s) to within 0.05 unit for typical student data with an uncertainty of f 0.1 in the experimentally determined pH values. The program has been used for the analysis of monoprotic acids, dipmtic amino acids, and with minor modification for redox titrations. Copies of the program, representative student data, and results are available upon request by writing to M.L.L. a t the Department of Chemistry, Montclair State College, Upper Montclair, NJ 07043.

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Kinetics Simulation Program G. L. Breneman Eastern Washington State College Cheney, 99004 The kinetics simulation program described by W. C. has been rewritten in the Basic language. The program simulates the spectrophotometric study of the rate of the reaction Cr(HzO)5Br2+ + U3+ CrZ+ + U4+ + Br-. The rate law is of the form Rate = k [ C r ( H ~ o ) ~ BrZ+]O[U3+Ib[H+Jc. The student choose3 concentrations and volumes of the reagents, wavelength, and cell path length. The computer outputs observed ahsorbances for times specified by the student. From this absorhance data the student must determine the values of k, a, b, and c in the rate law. The program helps the student analyze the data after each run by offering an initial rates calculation and/or least-squares fit of any or all of 8 functions of absorbance versus time to the data. (This differs from Child's original version which displayed a plot of the 8 functions.)

I Child'

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