been interfaced via RS-232 ports or probes have been interfaced via game ports. Two experiments that have been incorporated into our laboratory program have already been published. These a r e "The NOz/N204Equiliblium Experiment" ( 1 ) a n d "KineticsLab: The Crystal VioletBodium Hydroxide Reaction" (2).In addition we have developed an experiment on determining the molar masses of several gases from measurements of the soeed of sound in each (3). . . We continue work on a computer-mediated experiment on volumetric techniques in which each student is asked to measure a particular quantity of water with a pipet and the computer monitors the accuracy of the measurements and remedial. multimedia feedback when errors are made. As an example of the type of experiments we have developed, consider the kinetics of crystal violet. This experiment is done during the second semester of the two-semester general chemistry sequence--annual enrollment 1800 students. Students use a simple, computer-interfaced colonmetcr to collect absorbance versus iime data for the decomoosition ofcrvstal violet bv sodium hvdroxide. Called a "foktronic", th;colorimeteris constructed from a cube of polystyrene foam, a green light-emitting diode, and alightintensity probe of the PSL. The experiment consists of calibrating the instrument, generating a calibration curve of absorbance versus concentration of crystal violet using several standard solutions, and carrying out several kinetic runs in which the concentration of sodium hydroxide and the temperature are varied. The temperature of the reaction is measured with the PSL temperature probe. Absorbance data are collected directly by the computer and plotted in real time as the reaction proceeds. About 150 data pairs are collected in each kinetic run. Students are asked to carry out one run outside the foamtronic so that they can correlate the disappearance of color with the descending curve they will see the computer screen. Once data have been collected they are analyzed using a spreadsheetlike program called Notebook (41,which is easier to use than the t v ~ i c a soreadsheet. l Students use the slope and intercept oi'the calibration plot to determine the concentration of crystal violet as a function of time; these data are analyzed using the integrated-rate-law method and the order with respect to crystal violet is determined. From runs a t different concentrations of NaOH. the order with respect to hydroxide ion is determined, and then the rate constant can be calculated. If time oermits. which is oRen the case in a three-hour lab period,'an acti;ation energy study can also be carried out: Our experiencc indicates definite advantages of the computer-based experiment over the experiment it replaced. First of all, the computerized experiment is more typical of the way a solution-phase kinetics experiment would be carried out in a research laboratory than was the clock reaction we used previously Secund, calihration of the instrument and thc real-time display of absorbance (and by implication, concentration versus time data provide immediate feedback that students can use to revise and refine their experiment during the laboratory period. For example, pipetting errors can be caught when the computer disolavs " the calihration curve. and students can then orepare new, more accurately diluted solutions before proceeding. Third, computerized data analysis not only provides students with experience in methods commonly used in real laboratories, but also speeds the process of obtaining reaction orders and rate constants so that the data can be-analyzed and interpreted within the constraints of a three-hour lahoratory period. The computerized experiment does pmvide a n enhanced educational experience for our students.
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Journal of Chemical Education
Acknowledgement We wish to thank John F. Cannon, David Whisnant, J. J. Lagowski, William R. Robinson, Olga Agapova, and Alexey Ushakov for their contributions to this effort in the form of software, experiment design, and pedagogical expertise. This project is partially supported under a grant from the National Science Foundation Leadership in Laboratory Development Component of the Instrumentation and Laboratory Improvement (ILI-LLD);DUE - 9150265. Literature Cited 1. Curtin.T A,; Wahlshorn.D.;MeCormieh.J.A. J. Ckm. Edue.: Soflunm 1981.48(2): abatran appeared in J. Chem. Ed=. 1981, 68, 781-782. 2.Cannon. J.F.:Dammon,S.D.;Hunaberger,L.R. J.Chprn.Educ:Soffum19847R(l); abatraetappesred in J. Chem. Educ. 1994,71.23&239. 3. Hunsberger, L. R.;Restikya, J.A.;Cammon, S. D.;Moore. J. W Chemistry 1151ab: UniveraityofWisronsin-Madison.Chemistry Department, 1992. 4. Rittenhouae, R. C. J. Chem. Educ: Soffiuon 1981, 4RU): sbstraet appeared in J. Chem. Edur 1981,68.221.
The Holy Cross Discovery Chemistry Program Robert W. Rlccl, Mauri A. Ditzler, Ronald Jarret, Paul McMaster. Richard Herrick COlege of tne ~ o Cross y Worcester. MA 01610-2395 We have develooed a laboratow-centered a ~ o m a c hto the teaching of b o h general and organic chemLtry ( I , 2). Rather than first learning about manv of the theories and principles of chemistry in-lecture and-then verifying them in the laboratory, we have the students"discover" the same principles during the laboratory session and then use their findings a s the subiect of subsequent lectures. In many ways Discovery ~abbratoriesfollow the pattern of discovery inherent in the scientific method. Thus, our students gain an understanding of both the content of chemistry and the process by which it is acquired. The rationale often given for teaching chemistry in the more traditional content-based approach is that students must spend time learning the b a c h o u n d material before they can participate in the process that is science. Althoueh this is a valid aooroach. we believe that there are waysto learn basic s k k and'concepts while being immersed in the scientific process. Our new curriculum, now in its f f i full year, addresses this concern for content while still focusing on process. The four-course introductory sequence is founded on laboratory exercises in which the students work individually and woperatively to discover for themselves many of the basic ~rinciolesof modem chemistrv Lectures and discussions are still important features ofthe courses, but they draw heavily from the students' experimental results and student-formulated hypotheses. Conversely, during the laboratory period, students often gather for group discussions to plan experiments, speculate on anticipated results, make ~reliminarvintemretatious. or plan additional experiments. The essence oyour approachis to have students "Discouer" the basic concepts . by .directly ..uarticiuatiw- in the process that is chemistry. The laboratory exercises that are a t the heart of our Discovery curriculum differ in many ways from the more traditional student exercises that are designed to verifv a principle with which the students are already familiar. In a Discoverv prelab meeting the facuttv member does not lecture on t h e concept students will investigate. Instead, he or she discusses related issues or raises a question for students to think about for the experiment. This helps to focus the students' attention on the specific issues under analysis. In order to accumulate sufficient data to discover basic concepts, each student is assigned a unique modification of the experiment. After experimentation is com-
pleted, the students assemble again and pool their data. The results of the p u p are then presented in such a way as to guide the students to "Discover" a chemical concept. Recent technological advances that have made high speed instrumentafor the undertion approp,.iate graduate laboratory have aided our process by expanding the range of topics that can be investigated in a discovery mode.
Discovery Experiments for First Four Semesters
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Semester I -Atoms & Molecules 1 Measurement: The Scientific Mdhcd
Semester I1 Organic I 1 Extraction-AcidIBased
a
Gravimetric Analysis of Silver Salts Synthesis of Nickel
2
Empirical Fommuias of Chloride Salts Atomic Spectroscopy Visible Spectroscopy of Metal Complexes Structuresof Infrared Investigation of Covalent Bonding Descriptive Chemistry
4 5
4 5 6
8
Chemistry/Rec~ystallization - Melting Point
3
6
7 8
Distillation Stereochemistly and Molecular Modeling Kinetics and Equilibna Preparation ofAlkenes Bromine Addiiion to Alkenes Addition to Dienes ElectrophilicAmmatic Substitution
Current Directions 9 We are currently draiting a Discovery Chemistry Instructors Manual, which will describe ap- semester 111 - organic 11 Semester lV Biophysical Chemistry proximately 25 discovery laboratory Each experi- 1 ElectrophilicAromatic Substitution 1 Equilibrium Vapor Pressures of Mixed and Pure Systems ment contains a n overview describing the concepts, pro- 2 Nucleophilic Substitution 2 The Effectof Solute upon the Freezing Point of a Solute in Solution ceases, and experimental proce3 An Introduction to Equilibrium dures. Instructor notes based 3 Nucieophilic Aromatic Substitution upon our 5 years of experience 4 Stereochemistlv of Carbonvl Reductions 4 The Esuilibnwn of Pmtein Denaturation with discovery labs are in- 5 Reactions of carbony1 compounds 5 Buffers eluded. The experiments listed 6 Analysis of Tiration Curves Substituent Effects On pGs in the table encompass the fwst 7 Quantitative Aspects of Spectroscopy four semesters of chemistry a t Holy Cross. 8 Predicting the Spontanetiy of Reactions New discovery labs are cur9 Heats of Reactions rently being developed in both 10 lntroductim to Kinetics general and organic chemistry. In addition, Toolbook-based hypermedia solhare modules are being Trust-New England Consortium for Undergraduate Sciwritten and will complement selected Discovery laboraence Education. tones and serve as a review source for the students (3).
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Acknowledgment
This work is being supported by the National Science Foundation award DUE 9254016; and the Pew Charitable
Literature Cited I. ~ i e nR.; , ~ i t z kM , .cham. ~ E ~ U C1991.68.228. 2. Jarret, EM.;MeMaata, P D. Teaching Organic Chhmistnwith StudeudtGen~ented 1nformatio":"JC h r n . Edue,in preaa. Herrick, R. S.;Jarref R.M.;DeekkrZ A Art ofrraehing Chemiswi grant aponaoredby themzer ~
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