In our program, i t is also advantageous to have the same computer and interface available for collecting data from other types of experiments such as emf titrations or gas chromatography. Given the principles of microcomputer control of the applied potential, as well as the capacity for reading the response signal, extension to other voltammetric experiments is an obvious possibility.
MOLDOT: Space-Filling Perspective Diagrams of Molecules Steven Brumby Australian National University Canberra. A.C.T. 2601, Australia The use of computers for molecular .. e r a.~ h i c is s an active field of research, partly hecause the techniques an: relevant to the design of drurs (111-13). The trrhniauesare alwavailable t o teachers who may occasionally wish to emphasize aspects of a molecule's 3-dimensional character. I have developed aprogram named MOLDOT for the IBM PC, which prints space-filling perspective diagrams of molecules using a dot matrix print&. ~ y p i c aoutput l is shown in Figure 10, where the program has been used to illustrate the intriguingly different structures of [2,2]metacyclophane and 2,ll-dithia[3,3]methacyclophane7, as determined by X-ray crystallography (14, 15). The source code for the main program is in Basic, and assembly language subroutines are called. A numher of molecular graphics programs have been written for microcomputers (16-24). Some of these programs use the graphics display capabilities built into popular microcomputers. Other programs output their results using plotters. The program described here seems to he the first which uses a dot matrix printer for output. The idea of representing a molecule as a collection of dots came from the impressive molecular graphics which have been achieved with callieraohic disolavs. . " . when the van der Waals surface of the mogcuie is shown as uniformly distributed points of color on a dark background (25,26). In that method of displaying molecules, i t is not usually necessary or desirable to eliminate the hidden surfaces. However. when one uses a dot matrix printer for output, i t is desirable to eliminate the hidden surfaces, to prevent confusion and t o give a satisfactory 3-dimensional impression. It is sometimes helpful in making sense of moderately complicated van der Waals surfaces if a skeleton of lines representing the bonds is superimpused on the diagram, as in Firure 10. The user u t the nrorram mav determine whether such a skeleton will he drawn. It is aiso possible to draw the skeleton without the van der Waals surface. This can be helpful when selecting suitable angles by which a molecule is rotated before being drawn, since a skeleton of bonds without a van der Waals surface is generated very rapidly. When the van der Waals surface is drawn, execution is relatively slow, even when the program is executed in its compiled form: for example, Figures 10a and lob required about 20 and 16 min, respectively. Execution times do not depend strongly on the numher of atoms, but rather on the total numher of dots, whether hidden or visible. A Darameter proportional to the separation between the dots on the molecule's surface must he supplied hv the user durineexecution. and this parameter has animportant influence on the execu: tion time. Run times could probably he improved significantly if the program were rewritten with greater use of integer, rather than floating-point, arithmetic. Another approach would be to employ an 8087 coprocessor to speed up the floating-point arithmetic. ~~~~
'This topic was suggested to me by Y. H. Lai.
328
Journal of Chemical Education
A single-sided MS DOS formatted disk with files comprising source code, executable programs, and data files, plus explanatory notes and details of the method of computation, is available from Project SERAPHIM. The package requires an IBM, or IBM-compatible, PC with a t least 192 K bytes of memory. Logitek, IBM, and Microline printers have been used successfully, but any dot matrix printer with a bit image mode in which the horizontal and vertical spacings between the dots are the same should be suitable. Control codes for the three printers mentioned are recorded on the disk and can he accessed by the main program. For users of printers with different control codes a utilitv Droeram is provided which can be used to record the required control codes on disk.
-
..
John W. Moore and Paula Mlles Eastern Michigan University Ypsllanti, MI 48197 Mabolm Rasmussen Australian National University Canberra. A.C.T. 2601. Australia Kenneth Hartman Ames High School Ames, IA 50010 Patrlcla Barker Minisink Valley High School Slate Hill. NY 10973 We have developed several laboratory exercises that make effective use of an inexpensive thermistor probe (27) and colorimeter (28) that can readily he interfaced to the game ports of several microcomputers (29). In addition we have designed adapter hoxes (30, 31) that bring the necessary signals from the game ports to the outside of the computer and standardize the process of connecting sensors to different types of comput& and we have de6loped software to collect and analyze data for each type of computer. Thus, for example, when Apples and Commodore-64's are used in the same laboratory the directions given to students can be the same for all computers, and thesensors can easily he disconnected when the experiment is complete. Detailed directions and instructor's notes are currently available from Project SERAPHIM for nine experiments. Thermistor Calibration (32) involves collection of temnam~--turelthermistor-reading 'data, least-squares analysis to fit the data to a nonlinear equation, and evaluation of the sensitivity and accuracy of the thermistor over different ranges of temperature. Heats of Reaction (33) uses the calibrated thermistor to measure increases in temperature upon adding acid to hase or hase to acid in a coffee-cup calorimeter. Collecting data by computer allows this experiment to be done as a titration where ten approximately 5-ml aliquots of acid (or base) are added to a 50-ml aliquot of hase (or acid). The data can then be analyzed by Job's Method to determine the stoichiometry as well as the heat of the reaction. The computer permits rapid data collection, allowing the experiment to he done in rouahlv half the time normallv required; also, immediate data analysis indicates possih6 ouesincorrect points and encourages . students to reueat anv " tionable experiments. Photochromic Kinetics (34) uses the computer-interfaced colorimeter to obtain absorbance versus time for the fast thermal decay of a photochemically generated reagent. Mercury dithizonate is irradiated with bright visible light using an overhead or slide projector and then allowed to decay ~
~
A~---
&
as well. All materials. includine experimental write-ups suitable for distribution' to studeks,'can be ordered frbm the Project SERAPHIM Catalog. .
Project SFKAPHIM is supported by the National Science Foundation, Grants No. SPE-LC!-6318: and SI'K-R1-00051. Views expressed in this article are not necessarily those of the National Science Foundation.
Exploring Chemistry by Computer: KC? Discoverer Aw Feng and John W. Moore
Eastern Michigan University Ypsilantl, MI 48197
b.
Figure 10. Space-filling diagrams generated on iBM PC by MOLDOT. (a) [2.2]Metacyciophane.wiihout hydrogens, based on ref. 14. (b) 2,ll-Diihia[3,3]metacyciophane,without hydrogens, based on ref. 15. from purple back to orange in the colorimeter, where the onlv light is provided by a meen LED. Without the higher speed data c&ection afforded by the computer it would be impossible to obtain the requisite number of data points, even a t low temperatures. ~ L c a u s the e reaction is rapid and can be reproduced simply by reirradiating the sample, it is ~ossibleto studv the effects of temoerature and catalvsts on the reaction and easily. ~ a i experimental y r i n s can be carried out and analvzed in a sinele class period. The other six experiments are shorter and are especially suitable for hieh school chemistrv laboratories. Beer's Law with the ~lock&onicI is a simplecalibration of the colorimeter using Cr3+ion solutions. Kinetic Study of theDecomposition of Thiosulfate in Acid involves precipitation of sulfur by acidification of thiosulfate and is based on a standard kinetics experiment. Kinetic Study of the Reaction of Ferric Ion with Iodide Ion measures the absorbance due to 1 2 produced when iron(II1) . . oxidized iodide. Cooline" and Heatine Curve provides for continuous monitoring of the temperature of lanric acid as i t is cooled and then reheated through its melting point; two thermistors are used, one for thelauric acid and one for the thermal surroundings. Simple Heat of Reaction is a computerized version of the standard experiment where stoichiometric amounts of acid and base are mixed but designed so that up to four students can use the same computer a t the same time. Freezing Point Depression of a Mixture involves a study of the freezing point of cyclohexanol containing different concentrations of benzoic acid. Currentlv software and adaoter boxes are available for ~ ~microApple 11e/i1+, Apple IIc, and d o m m o d o r e - 6 4 1 64 computers; they are being developed for IBM PC and PCjr
How would you like t o have a computer-searchable handbook of chemical facts for all the elements? KC? Discoverer is a program that provides students with just such a function. I t is based on the suaaestion made at the Proiect SERAPHIM Powwow I meet&; (35) that it might be possible to devise a computer program that would allow students to explore physical and chemical properties of the elements. An outline for such a program was provided in reference (35). We report here version 2.0 of KC? Discoverer, which includes most of the features suggested by Powwow I participants. KC? Discoverer consists of a database and several programs that provide quick and easy ways to explore, manipulate, and display graphically the data. For each of the elements 46 ~hvsicaland chemical orooerties are stored. (Fieure I1 shows the screen .display fbr hydrogen indicating which properties are included.) The program helps students (or facht;) to search for all elements thBt have particular property, to sort the elements in order according to a certain property, to graph any property against any other on a set of Cartraian axes, or to select elements according to the period-
a
DISCOVERED: 1766 mum cnsI(os: 10.5 ABUNO CRUST: No data. COST: 0.2 $ / k g ELEC.CONDUCT: Wo data. HARDNESS: No d a t a . TOXICITY: lor CObmON OX. NOS:
NANE: *TO)IIC NO: s m m :
m n m c w: DENSITY: ETATE(S.I.B); MELTING FT: BOILING PT: HT OF PUSION: HT OF YAP: THER CONDUCT: COLOR: RX r U R : RY u WATER: RX r ACID:
.
N W : ATOIIIC NO: S W L : NO. ISOTOPE:
colorlelP
burns explosival) none none
Hydrogen 1
H
3
1st 1 0 N . H G :
,318.0
2nd ION.EIIC: 3rd ION.ENG: bth ION.ENG: ELBC.APPIN: POLUIIUBILITY: ATMIIC VOL: COV.R*DIUS: IONIC RADII: 2
No data. No d a t a .
1 : (it):
(2,): (3+)2
kJlnol
No data.
73.0 kllmol 0.4 1 ' A 14.1 cm"31md 32.0 om
ELECTRONEC: 2.2 PORrmU OF HYORIDE: H2 P O W OF OXIDE: HZO,H202 QORINU OF CHLORIDE: MCI NO. ALLOTROPE: No data. STRUCWRE: No date.
NO *at.. No data. data. NO data. No data. NO
Figure 11. Screen displays t o m KC? Discoverer. (a) Macroscopic properties of hydrogen (b)microscopic proflier of hydrogen displayed on a separate screen.
Volume 63 Number 4
Agril 1986
327
