label enclosed, and either return U S . postage or appropriate international postage union certificates; and addressed to J. D. a t the address shown above. We would encourage user comments.
"QUIZMAKER-A Versatile Program for Chemistry Exams T. R. Shepherd and 8. M. Mattoon
Creighton University Omaha. NE 68178 Edward Carberry Southwest State University Marshall. MN 56258 "Test Maker" programs Can he a great aid to the chamistry professor for storing and utilizing test and exam questions. Unfortunately, most impose severe restrictions on the length of the questions as well as to the length and nature the answer choices. We IePort a program that One to construct exams or quizzes where the length and nature of the questions and/or answer choices are unrestricted. Thus, subscripts, superscripts, other s ~ m b o tables h of data, and all ~ r i n t e control r characters for any printer may be incorP0rated into the text of the questions and answers. he program, written in Word Processor Language, is designed to operate with the Apple Writer 11word processor and an Avvle IIe comvuter. Because the resultina file can be easily moiified by the word processing program, this software is more versatile than any of the others we have examined. Exams are constructed by specifying file name and question number for each desired test item from material previously designed by t h e instructor. Output consists of the constructed exam text file and an answer key displayed on the screen and ready to edit, save, and/or print. Test items appear in the order specified by input. QUIZMAKER is available from Project SERAPHIM on a 5'/a-in. disk.
Laboratory Report Writing In General Chemistry Using Computer-Assisted Instruction J. Charles Templeton and Carmen M. Loren2
Whitman College Walla Walla. WA 99362 T o enhance student learning in preparing laboratory reports, 12 interactive FORTRAN programs have been developed for use by students in the first-year lahoratory. One, "Computer", is designed to teach inexperienced students how to use the computer terminal and to become familiar with the interactive mode of communication with the computer. The other 11programs are designed for use following the comnletion of a snecific laboratorv in the " exneriment . laboratory text (I)or on a handout. The programs are written toassist studentsin relating experimentto theory, and in analyzing their data in such a way that they will discover sources of error in reasonine and/or calculatine and thus will be able to see that the final results of the experiment do support the theory. Students using these optional programs have gained a better understanding of the experiment and have improved the accuracy of their calculated results pared to students who have not used them. Following completion of the laboratory experiment, the student logs on to the desired program using his or her desk number. Through a question-and-answer format involving theory, nomenclature, laboratory techniques, and numerical
manipulation of the experimental data, the program guides the student through a review of the theory and the calculations needed to generate the final results. Student input involves data, numerical and word answers to questions, and selection of appropriate multiple choice responses. Hints are provided and repeats of questions or sections of the program are often permitted. The data tables in the program are set up similarly to those in the laboratory text whenever possible. Standard Features of All Programs (Except "Computer") Associated with each program is a data file, inaccessible to the student user, that contains student desk numbers and true or expected values for any unknown(s) used in the experiment. If tables are being filled in, the prompt shows the student where the data will be entered. Each program checks the validity of the desk number given by the user against the data file and willahort after twoincorrect inputs. Experimental values determined for the unknown are compared with the true or expected value stored in the data file, d, the deviation is reported to the student, various checks on consistency of student data and results are performed, depending on the program. Selected final results, the student's answers to questions (whether correct or incorrect), and of the options (such as ,.hecks on the data) are stored in the data file at the completion of program execution. Each program contains various routines, accessed by appropriate desk numbers, for the instructor to load, correct, and list the data file, and to run a "stripped" version of the program, containing only the data input and calmlations, for use in grading student lab reports. Brlef Descrlptlons of Each Program Abbreviated comments on each program are given below. The exveriment number in Slowinski et al. (1) . . follows the program name. ALLOY (8): Determines percent aluminum in Al-Zn allay based on volume of hydrogen gas produced when sample is dissolved in acid. Checks student's interpretation of his graph of "moles of hydrogen per gram of alloy". Determines if barometric pressure given bv student is within reasonable limits: cheeks if vanor of . vressure . water matches that in oroeram's data table.
student's understanding of theory, especially concepts of endothermieity, exothermicity, and temperature changes during these processes.
CHROM (3): Com~utesRt values for known and unknown ions in paper chromatography of colored ions of transition metals. Cheeks knowns against 'standards'. Gives range of colors against which to match known and unknown. CO411'1VER: Introdures terminal keyhonrd to novice user after minrmnl sign-on instruction. I'rovides wme flexibility of t e ~ det pendine, on style id terminnl bring used and uaer's familiarity with typewnrer kryboard. Requires no data or calrulntions. CRSSTAI. 12,.romputea grams and percentages from fractiunal rrvrtaliination of mixture of NnCI. sand. and K,Cr?O-. Also comp& purity of K&07 in ppm from spectrometer reading. Permits entry of spectrometer reading as either absorbance or transmittance. ~. ~.. EI.KCEWL r15): Ikrerminer gram equivalent mass of unknown metal by elrctrolysrr and collection uf hydrogen gasevolved. EQIIII.IH (141: (:ompurrs equililrrium wnstnnt for transitionmetal complex ion based on composition of various solutions and their ahsorbauces in visible region. Constructs simple calibration graph showing student data points and linear least-squares best fit line. Checks student's determination of concentrations from absorbance values. FREEZE (19): Computes gram molecular mass of unknown organic acid from freezing point depression data. Displays rough graphof student's cooling curves, if desired, and determinesfreezing points of those curves so student may compare his evaluation of data. Determines if correct mass of sample was used in second run. Evaluates reasonableness of solvent and solution freezing mints. Calculates expected freezing point depression of unknowns&tion based on true value and identity of unknown compound. ~~~
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Volume 63
Number 10 October 1986
839
GEM (20 plus our revisions to procedure): Computes concentration of standardized base and determines gram equivalent mass of unknown acid. Checks if student knows correct gram equivalent mass of standard, oxalie acid. IODINE (15):Iodination of acetone kinetics. Computes concentrations of reagents, rate of reaction,order of reaction, rate constant, and prediction of time of reaction for additional reaction mixture. Cheeks to see if mixtures made by student are such that ratios of rates can he solved for reaction order; checks which ratios can be solved for which order. LIMITING (handout (2)): Demonstrates principle of limiting reagent by recovering product of reaction between NasP04 and BaCI2.Results indicate amounts of reactant in two initial solutions. Checks student's assumption of correct limiting reagent against actualone; checks his or her understanding of correct reagent to add to recover second crop of product. SOLPROD (22):Determines solubility product of PhI2 from speck a l data. Avallablllty 01 Programs All programs are written in interactive ANSI-standard FORTRAN and are run from HP-2645 or HP-2621 terminals (nongraphics, minimum of 80 characters per line) on an HP-3000 Series 111 system. Execution of longest program requires 22K W h i t words. Hard copies of selected sample executions available for 55. Source listinas and some sample executions provided on your 9-track, ASCII, magnetic tape at 1600 or 6400 BPI for 510. Format of returned tape will he 80 character record, unblocked, fixed record size, ASCII. User instructions also provided. Send requests and/or blank tape to J. Charles Templeton a t ahove address; make checks payable to Whitman College Computer Services. Specify desired tape density and system on which programs will he run.
Table 1. EHed ot lncreaslng Cube Size on the Calculated Madelung Constant for the NaCl LaHlce Ions per cube side
~adelunjlConstant
Percent Enor
2
1.45603 1.56654 1.62672 1.65493 1.67361 1.68501 1.69391
16.7 10.4
1.74756
on
3 4
5 6 7 6
...
-
.. .
6.6
5.3 4.2
3.6 3.1
...
Figwe 5. Onedimensional anangemem of f w r NaCl units
Calculation of Madelung Constants In the First Year Chemistry Course Mark Elert and Edward Koubek US. Naval Academy Annapolis. MD 21402 Figure 6. Cublc arrangement of four NaCl units
One of the most important topics in anv. beginning chemistry course is bonding. ~ n f o r t k a t e many l~ students are left bewildered by the quantum mechanics required to explain the formation of eovalent bonds and simply accept their professor's word that the sharing of electron pairs results in bond formation. This need not he the case ?or ionic bonding, as most students can visualize the simole conceots involvine electron transfer followed by ~ o u l o ~ hattrktion ic of theresulting ions. We first have the students consider four NaClunits in a linear array, as shown in Figure 5. The total potential energy associated with this arrangement of ions can be summed as follows:
magnitude of the coefficient in this potential energy expression, so we would say that the Madelung constant for an infinite one-dimensional NaCl crystal is 1.39. Of course, real crystals are not one-dimensional. This must mean that the potential energy can he lowered further by arranging the ions in a three-dimensional rather than a one-dimensional array. T o investigate this we again consider a system of four NaCl molecules, but now in a three-dimensional array as shown in Figure 6. The change in potential energy due to ionic bonding in this arrangement can he calculated as follows:
Dividing by four yields a change in potential energy per NaCl unit of -1.27e2/ro. Such an arrangement is 27% more favorahle than the simple molecular form for which the potential energy is simpiy -e2/ro. Clearly the same calculation applied to an infinite chain of NaCl units would lower the ene& still further. The ootential enerev can actuallv he evaluated quite easily in this case by summing the appropriate infinite series analvticallv" (3). . .. and the result is -1.39e2/m per NaCl unit. The ~ a d e l u nconstant ~ is defined as the
Dividing by four now gives a change in potential energy per NaCl unit of -1.46 e2/ro. At this point most students are willing toaccept the fact that, if one were to ronsidera much larger number of NaCl units in a three-dimensional array, one could arrive at a final value of -1,747558 e2/r... In fact. convergence of the method descrihed here is quite rapid: With a simole comouter oroeram. students can easilv calculate the ~adelungcons
