Wllliam M. Butler and Henry C. Griffin University of Mich~gan Ann Arbor, MI 48109
Simulations in the General Chemistry Laboratory with Microcomputers
T h e flurry of activity i n microelectronics, which some observers consider t o b e a t r u e technolonical revolution ( 1 . 2 ) seems likely t o send a second wave through t h e medium of chemical education. This new disturbance nortends even grearer impart thim that rattsod by the spread of pocket calculators. T h e cause of the disturbance 1s the microcomputer, n descendant of both the computer and the calculator. \Ve d o not intend t o b l a h o r the distinction between evolution a n d revolution, h u t some indication of t h e quantum j u m p i n economy.resulting from microelectronic circuits will serve a s a useful orientation. Three vears aeo. when we beean t o look for equipment suitable for interactiGe $imulations,ihe most attractive choice seemed t o b e video terminals driven b y a remote computer. E a c h of these terminals would have cost a t least $5000, exclusive of costs associated with t h e computer. A t a b o u t t h a t time T V video games were making a big splash in t h e consumer market. These games contained most of the components needed for simulation, yet they were available a t 1/30 the price of the terminals. Inexpensive parts were available for upgrading t h e games t o a computational power adequate for teaching applications, a s demonstrated by hobby computers' based on single chip microprocessors. T h e problem was t o transform the available parts into a n o ~ e r a t i "n esvstem. Naivelv one mieht consider this t o b e a .. relatively minor question nf establishing dectrical cumpatihilits a m m r the Darts. hut the real rhalleune isdevelopinn rhe systkm programs which permit efficient c&nmunica&on between a user a n d t h e comDuter. Fortunately, several manufacturers had perceived sufficient d e m a n d for home computers to venture thesignificant i n v e s t m e n t s r e ~ u i r e dt o design a n d produce these8ystems. Matching Computers with Applications The importance of system programszcan be seen by a comparison of the two computers, the PET 20013and the APPLE 114,with which we have had themost experience. We had identified three main areas of potential application of microcomputers: (1) Laboratory simulation (2) Classroom computations beyond the capabilities of caleulators (3) Graphics displayed with color videomonitors in a largelecture hall: Although both the PET and the APPLE (and several other microcomputers) are based on the 6502 microprocessor, they have quite different features. The APPLE provides color graphics in two different resolutions and character formats, hut a complete system consists of several separate components. The PET is a complete system in a single cabinet, and even though it has valuable special characters for graphics, it does not generate color video signals. Because of its extreme portability and ease of programming, we selected the PET for interactive simulations in our laboratory course. We recognize that, in a manner similar to the nearly steady flow of developments in calculators aver the last 10 years, perhaps better and cheaoer m i c m m ~ u t e r are s iust ahead. For that reason. in this reuort
computations will be presented in future articles. Course Context Although we feel that the applications described below are compatihle with most general chemistry progrsms, some specific features mav deliye from the unusual format of our one semester laboratorv
cluding a small group of very well prepared students who take "honors" chemistry). Both groups use essentially the same syllabus, but the more advanced students take laharatow concurrent with the first term lecture course while the other group takes it concurrent with the second term lecture course. The weekly schedule of the lahoratory course consists of a "prelab" lecture, a laboratory period, and a "postlab" diseussion. The prelab lectures are given to large groups 1to 3 days prior to the associated laboratory periods. These lectures include demonstrations, necessary chemical principles, and details related to the particular assignments. The 4-hr period which is scheduled for lahoratory and discussion consists of 3-3% hr in the lahoratory fallowed by 112 to 1 hour of "postlah" in a small classroom. 'l'he computers are wed in rhe lahwatury a i n supplemtnt to thc rr:ular " w e r " e x p c r i m e ~ ~ t . ' r h e s t u d mhring t ~ rhrw la11m,trbuuk tu the wmputm nnd record rheir results a i part oirhe regular labowwry period. The computer programs require the student to make choices about experimental conditions and simulate the Consequences of those choices (in our view, he mast powerful form of computer-assisted instruction). They provide a chance for students to make decisions and mistakes-an important aspect of learning, all hut eliminated in the regular laboratory exercises through efforts to economize on time and materials. In addition, the video display of the PETmicrocomputer allows useful graphs and line pictures to be incorporated. We have approximstely 1000 students in our laboratory course. A maximum of six sections, of twenty-four students each, meet simultaneously. Thus, with eighteen machines we have a minimum of three PETS Der twentv-four students to use durine the 3% hr oeriod. We ~
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is very popular with the students. Obviously there are many other ways to use computers as part of chemistry instruction. Our approach is illustrative of the impact these versatile new machines can have. Characteristics of the Computer ThePET computer3 is similar in size (46 cm wide X 41 cm deep X 36 cm high) and weight (20 kg) to an upright typewriter. It communicates to the user by displaying text and diagrams on a 23-em diagonal raster-scan cathode-ray tube. The user can write programs and interact with the computer through the keyboard, which consists of two rectangular pads5 with a total of 73 keys. A built-in cassette transport can be used to stare and load programs. Out PETS have 213 hits ("8k bytes") of RAM6, which gives about 7000 bytes for user
detailed knowledge of internal structures in order to program and use. "Home computer" is used for a similar system in terms of components, hut one which is designed far use by nons~ecialists. 2By system programs we mean all programs, both in read-onlymemory (ROM) and read-write-memory (so called random-areessmemow RAM) which are suoolied .. bv the manufacturer and which serve as the starting point for user written programs. Commodore Business Machines, Inc., 901 California Ave., Palo Alto, CA 94303. 'Apple Computer Ine., 20863 Stevens Creek Blvd., Cupertine, CA 95014. The character set includes all those of a standard typewriter, but the spacing is too close to permit "touch typing" even by someone who masters the idiosyncratic layout of the keys The PET computer can be purchased with 4k bytes of readwrite-memory, hut this size is too small far most of the applications we have investigated. Volume 56. Number 8, August 1979 1 543
programs in addition t o the 1000 bytes needed t o store the CRT display information. The cassette can load a full size program in about 100 sec. When the power to the PET is turned off, all user programs in RAM are erased, but the extensive system programs stored in the 14k bytes of ROM are available as soon as power is restored. These permanent programs determine many of the special characteristics of the P E T
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The provision for special graphics eharacters is of particular significance to our applications. Without such characters the displays would be limited to that whieh a n be done with a standard twewriter without releasing the paper or the single space line feed. T& PET'S CRT display consists of 25 raws of 40 characters. Each character space is a 8 X 8 dot matrix. Thus the entire display is a 200 high and 320 wide dot matrix. If each of these dots could be controlled independently, a quite detailed figure could be drawn. Such control would require 64 bits of information far each of the 1000 character spaces. The 8-hit byte, whieh is actually available to identify the unique pattern for each character, is capable of Z8 = 256 distinct choices. Letters, numhers, and common symbols require only about half this number of choices; the remainder is used to define eraohical svmbols. These svmhols are .. . verb ~u~efid in dmmvmg line d~ngmmc,rrctan&r wwdinateploti (31 X ,411 ris~,lurlont.and h:,r 6mph+ 125 X XOur 200 A rewlutim). hlore detail* un the n m p u t c r can be obtained from recent wer reports (3).
Figure 2. Rates-of-reactionplots. These graphs show the effectof the relatively coarse grid (50 high X 80 wide)availablewith the standard graphics characters. The linear plot (part a) should be a smmth curve. and the semilog presentation (part b) should be a straight line.
Types ol Applications Perhaps potential users of microcomputers can extract more information from examples of applications than from technical specifications. Some of the desim elements whieh can be imolemented with tlw I ' I X arc illuitmr?cl in the fdlwing sulhntnms. In most cnsrs the intent is that thr
