rw
Figure 4. Oraphiw screen print hom simulated polymerization experiment. initial mnomer Concennation, 1.0 M; initial initiator concentration. 0.01 M; kinetic chain length. 359.4.
NUMBER FRACTION DISTRIBUTION OF DECREE OF POLEiTE09 FREE RADICAL POLYMERIZATION ERMINATION BY COUPLING Figure 5. Graphics screen print of theoretical curve. Kinetic chain length. 359.4.
screen. At a pause in the program, the screen can be printed, orovided that the anorooriate oroeram (GRAPHICS.COM for IBM) was called1;efdre thebo?;mer experiment simulation hegan. After this, the program plots the weight fraction distribution and again pauses for screen print. In the case of the coupling simulation, the variable U is transferred to PLEN[I], in which I is 1 or 2; PLEN[l] is added to PLEN[2] in variable J, which serves to determine a variable, DP[J], which is incremented by one a t the end of the loop. This gives the effect of combining two chains by coupling. The remainder of the analysis is identical to that for termination by disproportionation. In addition, the program can be used to plot on screen the theoretical curves for number fraction distribution and weight fraction distrihution for termination by disproprtionation and for termination by coupling.
Spreadsheet Graphics in the Organic Laboratory: Providing Students with Feelback mlhmr Data I Jeffrey E. KeIsm
Coa College
Cedar Rapids, IA 52402 ContribAors to this and other iournals have recentlv discussed the uses of microcompuier spreadsheets f o r k c h anolications as eradine- .(19.20). calculation of activitv coeffi. c&s (21), anrfscientific modkl building (22). ~ e v k o v(23) has pointed out the advantaees for aoolications in the scientific.lahoratory of "second.gkerati&spreadsheets" such as LOTUS 1-2-3 with their powerful graphics features. Lev796
Journal of Chemical Education
FRAC DISTILLATION
Figwe 6. Fractional dlstiilation data. Fmm top to bonom ourves are: wt % toluene in lraction3: wt % methanol in fraction 1; volumeof fraction 1: volume of fraction 3.
kov's examples were principally physical chemistry ones. I t is the ouroose of this DaDer to illustrate uses of secondgeneraiion-spreadsheets inthe organic lahoratory. I have no brief for anv particular brand of snreadsheet-we use SunerCalc3 (the-current version is 4) principally because it is available to educational institutions a t steep discount. Clones of LOTUS 1-2-3 are available a t low cost, but two of them are the subject of current lawsuits. Lotus has recently made available a $40 student version of their spreadsheet. While these spreadsheets were originally written for IBM comouters and comoatibles. versions of SuoerCalc3 and a t lea$ one of the clones are available for the Apple I1 series. With the exce~tionof Der cent vield calculations. orzanic chemistry has tiaditionahy been;egarded as a qualitkive subject. However, modern snectrosco~icand chromatograbhic instrumentation allows us to a&umulate quantitative data on student samples. While academic chemists aenerally appreciate the calEulating power of spreadsheers;not all are awareoftheir powerful graphics features, which make nossihle the comnarison of student data whether or not one does calculations. The dramatic impact of seeing their class data disolaved eraohicallv on a color monitor is much more effectivethan graph pape; at getting students to think about their data. Figure 6 represents class data for the fractional distillation of 25 mL of an eaual-volume mixture of methanol and toluene. The students-collected the bulk of the distillate in fractions 1 and 3 and a small intermediate fraction. They analyzed fractions 1and 3 using a gas chromatograph interfaced with a computing integrator. The resulting data were then entered into a worksheet, and the graph shown in Figure 6 was displayed to the class on a 25-in. color monitor. Since the first fraction is an azeotrooe cdntainine 72%meth1 and 28% toluene, it is larger in volume than the third (the bottom line in Fie. 6 ) . which is nearlv oure. (The student data averaged 97 &%toluene.) The incriased purity of fraction 3 relative to fraction 1 and the large ~. - deeree " of precision in the student data are readily seen by inspecting Figure 6. Student 10 noticed her puritv for fraction 3 was less than that of anyone else in the class,thought about her experiment, and realized she had started collecting fraction 3 significantly below the l l l ° C boiling point of toluene. Commercial bleach is tending to replace dichromate in the organic teaching lahoratory for the oxidation of cyclohexan01 to cyclohexanone (24 and references therein). When students make cyclohexanone according to the procedure of Mohriget al. (24), the product usually contains small quantities of cyclohexanol and can he analyzed by gas chromatog-
Table 3. Ethanol Oxidation Data*
CYCLOHEXANONE PURITY
" ' I Time
Absorbance
(Ao A,- A,
(A,
-A 4 - A,)
In Y
In Y Halft
life
aaaptsd f r m ref. ZB 1\11 calcvlatlonr done by the spreadsheet
Figure 7. Purity of
and the reaction half-life is given by (In 2 ) h . Table 3 is similar to the one in ref 26, but here the spreadsheet has performed the calculations. Sophisticated spreadsheets can also do certain types of regression analysis. Figure 8 shows a SuperCalc3 least squares fit to kinetic data from Table 3. The spreadsheet calculated k as 0.226 f 0.013 and the intercept as -0.036 0.028 at the 95% confidence level. The kinetics example above uses the spreadsheet's calculating abilities. All three examples use the spreadsheet's rapid and convenient graphics capabilities to reach human beings' intuition in ways that tables and words cannot match.
cyclohexanme samples.
*
Acknowledgment
I wish to express appreciation to the Pauline Morris Trust for grants to the Coe College chemistry department for the computer and large color monitor and to Vernon Melcher and Bess Naujoks for helpful conversations. -I 0
I
2
3
5
I
6
Tim.
Figure 8. Leastaquare6fit 01 kimtlc data fromTable 3. Y is column 4.
Use of an 8087 Co-P ocessor Chip to Speed Up
LomoT
raphy. Entering the resulting weight per cent data into a SuperCalc3 worksheet yields the graph shown in Figure 7. This graph stimulated a great deal of discussion among the students since there clearly are two sets of results. The purities for students 1-6 were 56-73 wt % cyclohexanone, whereas students 7-13 got 90-97 wt %. When the students were identified, it developed that those who started earlier obtained the less pure product. Furthermore, one of the students in the second, higher purity, group remembered that he was the first to use a freshly opened bottle of bleach. Conversations with storeroom personnel revealed that the first bottle had been first opened several months before. Before long, the class was able to come up with the sensible hypothesis that the older bottle had lost some of its oxidizing agent through evaporation of chlorine during the months of storage. Kinetics is an area of organic chemistry that can benefit from both the calculation and eranhics abilities of soreadsheets. The rapid graphing capakl&y of spreadsheetsmakes the conventional plotting tests for first- and second-order kinetics very convenient. Coe has recently described the use of the Euler-Cauchy method with SuperCalc 3 (25). The disappearance of dichromate during the dichromate oxidation of ethanol can he followed by the change in absorbance a t 440 nm. A popular organic laboratory hook has such an experiment in which a large excess of ethanol makes the reaction pseudo-first-order (26). Under these conditions, the rate equation assumes the form kt = In (Ao - A,)I(At - A d ,
Steven Brumby Australian National University Canberra. ACT 2601. Australia For numher-crunching applications, an Intel 8087 co-processor chip is a useful addition to the IBM P C K T and compatibles. Programs run faster, and may give more accurate numerical output, if one uses a compiler or interpreter that exploits the co-processor for arithmetic. Another way of benefitting from the co-processor is by writing Assembly Language subroutines that use 8087 instructions. With many computer programs it turns out that a large proportion of the exkuti& time is occupied with a relatively small proportion of the code. In this situation, a logical approachis use a highly convenient language, such as BASIC, (even though it may not be efficient), for the major part of the program, and a highly efficient language, such as Assembly language, (even though it may not be convenient). . . for the com~utation-intensiveportion of the program. Creating 808718088 Assembly-language subroutines is most satisfactory using Version 2.0 or later of the IBM or Microsoft Assemblers, but is not impossible with the earlier versions. Such subroutines are not only faster and more precise hut also are easier to write than analogous suhroutines that use only 8088 instructions. A book by Startz (27)is a valuable source of information on writing 808118088 Assembly language subroutines that may be called from BASIC. Volume 65
Number 9
September 1988
797
