Purdue Unlverstty West Lafayette, Indiana 47907
Programmable Pocket Electronic Calculators in the Classroom
Program for a Quantitative Approach to Chemical Equilibrium
Robett W. Weldert "ittenongo High School ?hittenango, New York 13037 The use of programmable pocket electronic calculators :PPECs) is increasing and their importance in the chemistry :lassroom can and should be great. With the decrease in price ,f many sophisticated PPECs, time consuming and tedious :alculations can be performed quickly allowing students to 'ocus in on chemical concepts and teachers to use complex :rading systems.The benefits mentioned in Garst's article on 'Grade Analysis with a Programmable Pocket Electronic :alculator"' include ease and speed in programming which dlow both teachers and students with no programming ex~erienceto devise Droarams. For this reason it is ideal for . .. :omputntim d averages and wst scores, pading of reperirious at, cxtwises and immt,diure feedhark for srudencs checking .heir laboratory data and calculations. ;rading Many teachers grade tests on a "curve," hut few use a nornalized curve because of the difficulties involved in compu:ation. With the use of a PPEC, a normalized T Score (similar .oa College Board score) can easily be computed after finding .he mean and standard deviation of the test scores. T h e :omputationto score each test paper would involve: T = ( x - X)I(sx)).100 500, where Y is the mean score and s, is the ;tandard deviation2 Needless to say, this calculation would ,e quite tedious for 50 papers, hut with a PPEC these calcuations take only a few minutes.
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6. ENTER
7. HALT 8. [Enter Tube'Height Ratio]
17. 18. 19. 20. 21.
HALT, Record [SCNr,] x
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M.R. y +,Record Keq x
' Garst, J. F., J. CHEM. EDUC., 54,114 (1977).
Mehrens. W. A,. and Lehmann.. I. J... "Measurement and Evaluation in Education and Psychology," Holt, Rinehart and Winston, Ine. New Yark, 1973, p..15.l. :'Cattan, F. A. Darlington, C. L. and Lynch, L. D., "Chemistry: An Investigative Approach," Revised Edition, Houghton Mifflin Company, Boston, 1973, p. 664.
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.aborato4 Exercise Calculations The PPEC is aiso an invaluable aid in difficult lab compu.ations. The calculations involved in the CHEM Study exIeriment on Chemical E q u i l i h r i u m ~ o s ea problem to many itudents as well as a grading nightmare to many teachers. Nith a 100 step PPEC students can feed in their data immeiiately after their experiment, evaluate each equilibrium :onstant and spend time 'doing' the calculations later. Stuients need not program the calculator to use it; however more ~ b l estudents might devise programs of their own to evaluate .he equilibrium constant. T o check and verify all results more .apidly and with greater accuracy, the teacher need only use In appropriate program. The following programs written for the NOVUS 4515 Mathetician P.R. illustrate programs for T score grading and .he CHEM Study investigation on Chemical Equilibrium. r-Score Program 1. START
HALT [Enter Score1 ENTER [Enter F] fi. 2. 3. 4. 5.
328 1 Journal of Chemical Education
7. [Enters,] R +
Mass and Density-A Surprising Classroom Demonstration Harvey F. Blanck Austin Peay State Uniuersity Clarksuille, Tennessee 37040 During the last several years general chemistry students have been asked to compare two rocks and to select, using their hands, the rock having the higher density and the rock having the larger mass. The rocks used are: (1) a rock rich in iron having a density of about 3.5 glml and a mass of 350 g and (2) a sample of pumice having a dexsity of about 0.5 g/ ml and a mass of 540 g. All students select the iron ore as having the higher density and very nearly all select it as also having the larger mass. They are astounded when weighing reveals the immensity of their error. It appears that the hand measures or compares pressure rather than force and thus the heft of an object is more a measure of density than weight. (Geologists often determine the approximate density of rocks this way.) This may explain the existence of the question, "Which is heavier: a pound of lead or a pound of feathers?"
