B. G. Hughes and J. E. Bundschuh Western Illinois University Macomb. Illinois 61455
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The Use of a Hand-Held Proarammable Calculator in Evaluating Freshman Experiments
High enrollments in most beginning chemistry laboratories demand large investments of time and energy if evaluations of quantitative analyses are to be done with proper attention to details. Student results can be graded simply on the basis of the final answer compared to correct values, of course, but if calculations are to be rechecked and precision among replicate samples is to be considered as well, time requirements become prohibitive. The use of computers to evaluate student results has been a logical solution to the problem. With their high speed and huge storage capacity, it has been relatively easy t o write programs for large computers which store the correct values for a large number of samples, accept raw data from students and recalculate all results, make statistical calculations to evaluate precision for replicate samples, assign grades, and even make clever comments about the student's performance. We have written such programs and used them for several years. While they did relieve laboratory instructors of much of the tedious work necessary for evaluations, many difficulties were encountered in the process. Primary among these complications was the process for transmitting student data to the computer and returning the evaluation to the student. This practice required taking the student's data recorded on standardized report forms and punching it into cards. With the simplest format devised, at least two cards were required for each student evaluated. Many hours of key punch operation were logged and the incidence of punching errors increased as the time required for the job increased. After processing, the computer output had to be sorted by lab section and distributed to each instructor to be returned to the student. It was not uncommon for the evaluation to be returned to the student as much as two weeks after completion of the experiment, and occasionally it was worthless because of some error in recording, punching, or sorting data. We concluded that computers are ideally suited for the evaluation task but only if the students or instructors can have direct access to a terminal operated in the interactive mode. A computer terminal in every laboratory may be the ideal solution but it is prohibitively expensive and in many cases not available a t any price. The recent availability of programmable, hand-held calculators with several hundred programming steps and a number of addressable memories has provided a viable alternative to the use of a full scale computer for evaluation of quantitative laboratory experiments. At a cost of less than $200, the calculator has many of the same "in-the-lab" advantages of a remote terminal. For evaluation of quantitative laboratory experiments, we use a programmable calculator with the capability of both reading and writing on magnetic cards. This capability is important because it allows for storage of correct analytical values on a magnetic card ready for direct transfer into the memories of the calculator. Other features found to be useful are 1) the decrement-skip-on-zero (DSZ) function which alPresented at the Great Lakes Regional Meeting,stevensspoint, Wisconsin, June 7,1977 (Paper 95). 1 Detniled oroersms written for the Tems Instrument's SR-52 lmgrammablr rnlrulatornrr ~vnilahieon rrqursr from the Departmen1 of Chemistry. Wrrtern Illin& University. Maromh, lll~noir ~~
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61455.
336 / Journal of ChernicalEducation
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CHEMISTRY 2 17 KHP ANALYSIS
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(D) ACCURACY WADE (E) FINAL GRADE Figure 1. Student data repon form. lows for a combination of a repeated calculation with a counting operation much like a DO-loop in Fortran programming, 2) the indirect addressing for recall and storage which allows the retrieval of correct values identified by a code number, and 3) the capacity for subroutine functions which save needed space in the program registers whenever a particular series of operations occurs more than once in a propram. To facilitnre the input of student data, a report form was drvelowrl as illustrated in Figure 1. Students record their data in the Bpaces designated by boxes. As the program is run, the instructor records the calculator results in the underlined spares. To minimizr twors in running the program, corrrct key sequences are indirnwd b y letters in parenthesis following each entry. These user defi"ed keys which are labeled through E and A' through E' execute separate parts of the grading program which have been labeled for that purpose. A flow diagram of the program used for evaluation of a typical volumetric determination is shown in Figure 2.' The program is divided into six parts each ending with halt (HLT). Subseauent stens are initiated with the user defined kevs or a run ( H )statemmt. The first part stores the student value for mularitv of the titrant and initinlizcsother memories used for calcula~ions.The second is the looped portion of the program used to calculate the nercentaee of nroduct in each of three separate samples of the unknown. After the three calculations are completed the program is branched into a segment which computes the deviation for the three and, finally, the relative average devintian. In part four a subroutine is ralled to assign a grade for precision based on the relative average deviation just calculated and a grading scale pro~
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All direct volumetric titration procedures use simple variations of this basic program. Gravimetric procedures invariably involve simpler calculations and thus require a simpler is reouired. .oromam. .. A longer and more comolicated oromam . however, for grading an indirect volumetric titration method involving the back titration of a reactant added in excess. As a result, fewer memories are left for storage of correct values. The calculator function which allows data to be written onto a magnetic card and later read directly into the addressable memories of the calculator was essential to the success of this approach to evaluation of laboratory oerformance. The pro.cedure requires that a program be written assigningthe correct value for each unknown to a memory not used by the grading program itself. The resulting program is then written onto a magnetic card. Each analytical procedure requires a unique set of two program cards. The first card transfers the correct values into the addressable memories of the calculator and must be read into the calculator first. The second card transfers the grading program into the calculator. We have used a programmable calculator for evaluating student laboratory results in many sections of our general chemistry laboratory during the past academic year. Several advantages to this approach are now apparent. The time required to enter student data into the calculator and record results as they are displayed is such than an entire section of 25 students can be evaluated in less than 30 min. Of more importance is the advantage of giving a student the results of his experimental work immediately instead of requiring him to wait for as long as a week to receive his evaluation. Without exception students have responded favorably to this approach. Several advantages for the student are obvious. They learn their grade for each experiment as i t is handed to the instructor and thus have an opportunity to repeat the procedure a t once if necessary. Any calculation errors are discovered without delav and calculations mav be reneated while the procedure is s k l fresh in their minds. ~ i n a i l yop, nortunities to discuss orocedures. calculations. and erades karned are available immediately. These advantages c&pled with more subtle effects on the quality of our laboratory instruction have made the programmable calculators an asset to our total program.
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grammed into the subroutine. The grade is then stored for use later in the program to calculate a final grade for the unknown. The fifth part of the program accepts input of the code number which identifies the unknown and using the indirect addressing feature of the calculator recalls the correct value for the percentage from the proper memory. The average percentage calculated in part two of the program is compared to this correct value and a relative error is determined. The same grading subroutine used earlier is called again and a grade for accuracv is assigned. The sixth and final Dart calculates a weighted average of the precision and accuracy grade and displays the result.
Volume 55, Number 5, May 1978 / 337
