Karl E. Wiegers and Stanley G. Smith University of lllmois Urbana, IL 61801
The Use of Computer-Based Chemistry Lessons in the Organic Laboratory Course
Computer-assisted instruction is becoming an increasingly impo&nt aspect of the undergraduate chemistry curriculum. Applications of CAI to the laboratory have involved primarily and analytical chemistry courses (13).CAIhsing the PLATO IV computer-based teaching system (4,5) has been an imoortant suoolement to traditional learnine methods in .. the beginning organicchemistry courses a t the University of Illinois for several vears (6.7). . . . Recentlv. - . PLATO has been incorporated into organic chemistry laboratory courses as well. CAI may be used in several ways in a laboratory course (8). The present applications involve pre-lab CAI, in which the .. st&nt simulates an experiment & advance of actually performing it. and lah-substitute CAI, in which the computer is utilizedto simulate experiments which cannot be performed conveniently in the laboratory due to time, expense, or other limitations. In this reoort we describe the CAI materials developed for the organi'e lab courses, and present the results of ~roceduresdesiened to evaluate the effectiveness of CAI in this setting.
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and because students have difficulty understanding the calculations of yield and equilibrium constant in this reaction. In an average time of 40 min spent on the computer, the student goes through a presentation of equilibrium in esterification reactions and some sample calculations. The rest of the lesson contains a simulated experiment in which the student completes a table of data, proceeds through the reaction and work-up sequences, and finally calculates yield data and an equilibrium constant for the reaction. Exactly the same operations are executed when the student actually performs the experiment in the laboratory. The lesson on qualitative orzanic andwis allows the student to request the results observid when v&us chemical testll are applied to a randomly selerted unknowncompound,and control experirn&ts in which the tests are applied to Table 1. PLATO Lessons Used In Organlc Chemistry Laboratory Courses
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Lesson Materials PLATO is used in both a one-Semester elementary organic chemistry laboratory course for non-majors with an enrollment of 300-400 students oer semester. and in a smaller beginning synthesis laboratory course populated primarily by chemistrv and chemical engineering maiors. The students attend o i e lecture on the la6 m a t e r k each week and spend a 4-hr neriod in the laboratorv: the CAI materials can be worked'at any time convenient fi* the student. The laboratory activities in the non-majors course include five relatively simple experiments in which fundamental techniques are learned, five preparative experiments illustrating representative synthetic procedures, and two experiments requiring the identification of an unknown compound using qualitative tests, derivatives, and IR and NMR spectra. The activities in the chemistry majors course include some of these same experiments, in addition to more soph~st~rated organic and inorganlr preparations. Ten PIA'I'O lessons are used as a reauired. integral asnect of these two courses (Table 1). Each df the five L h n i q u e s exoeriments has one or two accomnanvine lessons. These lesions include both conceptual mate;ialkh[ch reinforces the discussions resented in lecture. as well as detailed simulations of theLexperimentsthemsklves. (Of course, the same techniques are used in the chemistw maiors course. althoueh a sepnr& experiment is not pert'ormed l%reach.) The IPSS&S are highly interactive, requiring the students to go through many of the same operations and decision-making proceuses that they do in the lah. For example, the lesson on liquidliquid extractions develops the concept of differential solubility as a basis for separating the components of a mixture, and oartition coefficients are discussed. The useof a seonmtory funnel is presented in detail, with numerous illustrations and animations. The use of an acid-base extraction scheme is described (Fig. 1). and to receive credit for the lesson the student must complete a simulated experiment on the separation by extraction of benzoic acid, p-nitroaniline, and naphthalene. A PLATO lesson accompanies the synthesis experiment on the preparation of methyl benzoate, performed in both courses. This experiment was selected due to its complexity 454 / Journal of Chemical Education
Avg. Time. min.
Lesson Title Determination of Melting and Boiling Points Melting Points and Mixed Melting Points Slmple and Fraamnal Disldlstlon Fractlona D~st~llatfon Experment Purification of Organic Compounds by Crystallization Liquid-Liquid Extraction Preparation of Methyl Benzoate AdSOrDtlon Chromatwraohv - . loentlllcat on 01 an Lnrnown Organnc Compound Use 01 the Perkm-Elmer Mmsl
.
20 20 d0
20 25 35 40 50 35
20
Conterns
Ref.
how to measure boiling and melting paints phase diagrams
(9)
phase dlagramr, apparatus eqwpmem, conlml parametars in simulation ~ ~ I ~ b l l i simulation lle~,
( 1 I)
solubilities. techniques. simulation simulation. calculations TLC. column. simulation chemical tests, knowns
( 14)
( 10)
I 12) (13)
.
115, (16) (17)
sample preparation, use of ( 18) instrument, sample spectra
Separation of a neutral ~ o n w n df m n an acid
Filter
1
I
Filter
U Rfter standim. the dryine aeent is removed by flltrotion.
Figure I . Display illustrating the operations involved in separating a nsmal compound from an acid by extraction of an ether solution with aqueous NaOH.
samdes of known structure. The student must then select the rorrict structure of the unknown from a list of possihilities. Por reasons of safety, economy, or availnhility ot'facilities, it is sometimes not possible to have students do a particular laboratory experiment. A computer simulation, while not heine an exact substitute for the real exoeriment, can be a valuable learning experience. We have used a lesson on adsorotion chromatoaraohv as a lab-substitute. Through extensive use of visu3 d&lays and animations the prikciples and applications of thin-layer and column chromatography are presented. To receive credit for the lesson the student must satisfactorily execute a computer simulation of the chromatographic separation of a mkture of benzhydrol and trans-stilbene. The student select3 solvents for T1.C experiments, and chooses an appropriate solvent on the hasis of the visualized TLC plates. Next the student is shown the components of a chmmatography cbhmn, which must be properly assemhled using the touch-sensitive panel on the PLATO terminal. During the elution orocess the student must replenish the elutLg solvent and collect fractions by touching the screen (Fig. 2). PLATO constructs a plot of sample weight versus fraction number, and the fractions are then combined to provide two samples of acceptable weight and purity. If the receiver overflows, or if the column is allowed to run dry, then the separation must be repeated. The use of this simulation lesson provides the students with detailed exposure to an imuortant technique which they do not encounter in the Table 2. Comparison of Average Tlmes for Completion of Each Experiment during a Semeoter with PLATO and a Semesler wlthout PLATO In Non-Malors Oraanlc Lab Course Number of
Number 1 2
3 4 5 6 7 8 9 10 11 12
Experiment
Lessons
Boiling Points
Melting Points Fractional Distillation Recrystallization Extraction n.Bulyi Bromide Methyl BsnmBte Methyl mNitrobenmate Cyelohexanone Chalcons Unknown I Unknown 2
Time without PLATO Time with PLATO
1 1 2 I 1
0 1
0 0 0 1 0
An additional lesson which has been utilized in the chemi s t maiors ~ course describes the use of the Perkin-Elmer 700 inf;arkcspectrophotometer, which is used by the students on several exneriments. Samole is discussed, and . oreoaration . . numerous'illustrations of spectra, hoth good and bad, are shown. The parts of the instrument are identified and a detailed description of the operating procedures is given. I t is expected that having students perform this practical lesson before using the spectrophotometer will result in more efficient use and diminished abuse of these valuable instruments. Evaluation of Lesson Effectiveness
Both objective and subjective data were collected in an effort to evaluate the efficacy of PLATO in the non-majors course. ~uhjective,perce~t
