An expanded version of PLOTTER enables the student to obtain a permanent copy of the data, the calculated values, and the graphs on a suitable on-line printer. The expanded program, named PLOTTER(REV. JM), was written for use with one disk drive and an IDS-440 nrinter. The Paper Tiger" (Integral Data Systems, Inc.) with graphics option, interfaced to the Apple I1 microcomputer through an Apple A2B0002 parallel printer firmware card. When only alphanumeric data are to be printed, PLOTTER(REV. JM) works by itself. I t requires only a suitable printer and interfacing. When graphs are to be printed, PLOTTER(REV. JM) loads a companion program named HRD from the disk. After printing a descriptive heading, PLOTTER(REV. JM) gives control of the micronrocessor to HRD which then causes the last-displaced graph' to be printed. (White or colored dots on the screen are printed as black dots on the paper.) HRD is written in binary and requires 36K bytes of RAM, one disk drive.. a ~ r eraohics .r i n t ewith " . caoabilitv and sufficient baud rate, and parallel data transfer. I t is slot dependent. The readers may request free single copies of the listing of the original or the expanded version of the program. Requests for obtainina the oroaram on a diskette should be accomoanied by $10 fmone; or2er or cashier's check in the name of i o n W. Mauch to cover the cost, postage, and handling. The authors express their appreciation to Joe Ruh for taking the photographs. ~
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where P is the pressure of the gas, R is the gas constant, T is the absolute temperature, V is the molar volume of the gas, a is the attractive forces constant, and b is the molar excluded volume constant. The voltage values are scaled so the readings on the potentiometer knobs represent the values in the usual units of T = Kelvin, a = 12 atm/mole2, and b = l/mole. The volume is allowed to take on 512 values, and the corresponding values of pressure are calculated. The corresponding points for the pressure given by the ideal gas equation are also calculated. The total time for reading the potentiometers and doing the calculations is less than two seconds. The calculated points are converted to analog voltages which are sent to the oscilloscope giving curves of the type shown in the photographs in Figures 6-8. Each curve, along with axes and tick marks, is plotted 64 times in order to give a continuous appearing display for three seconds. The potentiometers are then
Microcomputer Simulation Curves on an Oscilloscope Robert G. Ford Memphis State University, Memphis, TN 38152
Simulation programs are one of the most widely used types of computer-aided instruction (21). A useful type of simulation program evaluates a particular function of chemical interest and produces a table of values or a graph of these values. For examole. . . one mieht use the comkuter to calculate the concentration of a reactant as a function of time for a first order reaction. The o u t ~ uoft the Droeram could he in tabular . form or a plot of the familiar exponential decay curve. Numerous programs of this type have been described by Barrow
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Figure 6. Van der Waals and ideal gas curves for water at 600°C. a = 5.46 L2 ahn/moi2, b = 0.0305 Llmoi. The tick marks on the vertical axis are at 100atm intervals. The tick marks on the horizontal axis are at 0.1 Llmol intervals.
122) \--,-
For programs of this sort, we have found it advantageous to use a local microcomputer that obtains input parameters by reading voltages from potentiometers and plots curves on an ordinary low-frequency oscilloscope. The components of the system used for this purpose a t Memphis State are listed in Tahle.3. Similar results could he obtained on any microcomputer system that is capable of analog to digital and digital to analog conversion. A program that utilizes this system produces plots of the ideal gas equation. The calculations are done using a FORTRAN program, which calls assembly language subroutines for acquiring input data from the potentiometers and sending the output data to the oscilloscope. The program first reads three voltages from potentiometers to represent the temperature and the a and b constants in the van der Waals equation of state: P
Table 3.
= RTI(V - b ) - aIV2
Comoonents of Simulatlon-Dlsolav Svslem
b a t h H I 1 micrmomputer 40K bytes memory Date1 Systems SineTrac A/DD/A plug-in board for H I 1 Digital Equipment Corporation DecWriter 11 Heath H27 Dual Floppy Disk Drive Power SYDD~V wilh 3 Dotentiometers
520
Figwe 7. Same as Figure 6 except T = 647'C which is the crtt~caitemperature of water
Journal of Chemical Education
Figure 8. Same as Figure 6 except T = 700°C
reread, curves recalculated, and an updated display is provided every five seconds. This svstem has been used as a lecture aid in our elementm physical~rhemistrycourse. When discussing modifications c;f the ideal ms equation. one can rearlilv show the effect of allowing the gas molecules to have finite volume and attractive forces between them. One can also dial in the van der Waals parameters for a particular gas and adjust the temperature until critical behavior is ohtained, or search for the temperature required for near coincidence of the van der Waals gas and the ideal gas curves. Extension to other equations of state would he verv easv to make hv modifvine a few FORTRAN statements. ~ d d i G o n aprograms l for ithe; topics in physical chemistw. such as those described in reference (23) could also be writ&. We have found this system extremely easy to use, and student interest has heen high. A copy of the program listing may be ohtained from the author hy sending a check for $2 made out to Chemistry Department, Memphis State University. Figure 9. Typical chemical test simulation involving pipet, test tubes, graduated cylinder, and reagent bonle.
Organic QualitativeAnalysis with Dynamic Graphics Marvin J. Miller and James F. Johnson University of Notre Dame, Notre Dame. IN 46556 This paper describes "Organic Qualitative Analysis," a hiehlv interactive proaram used in couiunction with a s o ~ h omork organic c h e m i s h lahoratory. This software utili~esihe high resolution maphicscapahilitvof the A~)vleromrrutrr.and dfnamically depicts many wet ihemicai ieactions used in functional group analysis. Its Duroose is to acquaint the student betteFwith t h e d e d u c t i v ~ a p ~ m a ctoquditativeanalh ysis and to familiarize the student with the associated wet chemistry tests used in lab. Initially, the program randomly assigns to the student an unknown from a group of twenty-five compounds. The student is then informed that the identity of the unknown molecule must be determined from its nhvsical oronerties and the results of functional group tests. i n ; one of
