In the Laboratory edited by
Mary M. Kirchhoff American Chemical Society Washington, DC 20036
The Question-Driven Laboratory Exercise: A New Pedagogy Applied to a Green Modification of Grignard Reagent Formation and Reaction Jennifer M. Teixeira, Jessie Nedrow Byers, Marilu G. Perez, and R. W. Holman* Department of Chemistry, Idaho State University, Pocatello, Idaho 83209-8023 *
[email protected] Experimental exercises within second-year-level organic laboratory manuals typically involve a statement of a principle that is then validated by student generation of data in a single experiment. Irrespective of whether the experimental procedure is explicitly laid out or is developed by the student (in an inquiry-based fashion), the thought process for the student differs markedly from that used in a research setting. Moreover, these experiments are structured in the exact opposite order of the scientific method or thought process: namely, principle first with data as validation, rather than data interpretation leading to the development of principle. The result is often a lack of student engagement in the experiment (because students already know what the result should be) and a missed opportunity to provide students with the element of discovery that is at the heart of actual scientific investigations. Our goal is to craft a laboratory exercise that more closely mimics a research investigative process and orders student thinking along the lines of the scientific method (data interpretation leading to principle). An ideal forum for deriving principles from data within the framework of a second-year-level organic laboratory exercise is to discern between two competing proposed mechanistic explanations for a reaction. Discerning between proposed mechanistic explanations in a research context almost always involves logically connecting mechanistic observations (interpretations and propositions) from multiple experiments in a manner that is internally consistent. As such, the exercise described here involves the use of multiple data sets. Deriving Principles through Data Interpretation A unique pedagogical approach is employed that is designed to enable students to generate principles from data. Background information and data from a systematic array of previous experiments (both laboratory and theoretical) are provided (termed prelab data). The students then run a pivotal experiment, the data from which are to be interpreted and coupled to the interpretations from the prelab data. Finally, the students are provided with data from further laboratory and computational experiments (termed postlab data). The composite interpretations from prelab data, the data from the experiment performed by the student, and postlab data make it possible to distinguish between two mechanistic explanations so as to arrive at an internally consistent mechanism for a reaction. This approach is unique as applied, though it is not without precedent. The data-driven classroom (DDC) approach of Bondeson (1) entails providing students with a single data set for interpretation and subsequent derivation of a principle. The DDC pedagogical approach is primarily designed for implementation in lecture or 714
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for homework and is limited to the derivation of a single principle and is not incorporated into a laboratory exercise. Here, we expand the application of this approach to a laboratory exercise with multiple principles derived from manifold data sets that are correlated into a cohesive discrimination between two competing mechanistic explanations of a reaction. A second unique pedagogical approach employed is the use of guiding questions throughout the exercise. In a research context, the interpretation of data from a single experiment usually does not enable the scientist to completely solve the problem. Typically, the interpretation leads to new questions that frame further experiments. Ultimately, the interpretation of data from composite experiments (experiments tethered together through a cycle of experiment f interpret f question f new experiment...) leads to the crafting of an explanation. To facilitate students' ability to tether together interpretations from multiple experiments, the entire exercise (throughout the prelab data, the experiment, and the postlab data) is driven by guiding questions. These questions orient the student to the proper emphasis in the interpretation of the data they are assessing and are also used to guide students' thinking regarding the design and intent of the next experiment. The use of data from multiple experiments in the form of provided prelab data, student-generated experimental data, and provided postlab data organized via a question-driven approach is a pedagogy we refer to as the question-driven laboratory exercise (QDLE). The laboratory exercise proposed here involves a combination of computational data (provided) and experimental data (both provided and student-generated) (2, 3) with the primary focus being the interpretation of the data and a secondary focus on the gathering of the data. This general approach is applicable to a broad array of potential laboratory exercises. Schoffstal and Gaddis (4) have organized the body of published second-year-level organic laboratory experiments into four categories based upon pedagogical approach (summarized as entries 1-4 in Table 1). Our pedagogy is unique, representing a fifth approach (Table 1). The QDLE approach is instructorgenerated and inductive with undetermined conclusions and is further unique in that it is both entirely question-driven and requires that students correlate interpretations from multiple experiments into a unified thesis statement. Experimental Overview One of the most featured reactions in second-year-level organic chemistry is the Grignard reaction because the Grignard reagent is so versatile, enabling the synthesis of a wide variety of
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In the Laboratory Table 1. Comparison of Laboratory Pedagogiesa Pedagogy
Experimental
Primary Learning Approach
Conclusion
1
Expository
Instructor-generated
Deductive
Predetermined
2
Open-inquiry
Student-generated
Inductive
Undetermined
3
Problem-based
Student-generated
Deductive
Undetermined
4
Guided-inquiry
Instructor-generated
Inductive
Predetermined
5
QDLE
Instructor-generated
Inductive
Undetermined
a
Entries 1-4 are reproduced from ref 4 the fifth entry is a summary of the QDLE approach.
Figure 1. Question-driven flow summarizing the 33 questions in the QDLE into nine categories (represented as rectangles) and the corresponding experimental data used to answer those questions (represented as ovals).
functional groups. The Grignard reaction has been featured in experiments in this Journal 15 times (5-19) and an experimental Grignard procedure exists in almost every published laboratory manual. Despite the academic attention that Grignard chemistry has attracted, it is not a reaction that is used often in an industrial setting. Large-scale Grignard applications have diminished with time because of costs associated with the use of nongreen ethereal solvents. Moreover, safety issues are also a serious concern where bulk ether solvents such as diethyl ether (DEE) or tetrahydrofuran (THF) are employed. Thus, a green modification using a nonethereal solvent for Grignard formation and reaction is of interest.
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The QDLE for the green chemistry modification for Grignard formation and reaction has three overall goals (a detailed, step-by-step procedure can be found in the supporting information data). The students will: 1. Develop a new and greener solvent system for Grignard formation and reaction 2. Test the new solvent system via experiment 3. Discern which of two competing proposed mechanisms is more consistent with all the provided and student-generated data
The students will accomplish these goals by answering 33 questions that are sequentially embedded throughout the experimental
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exercise. To facilitate this process and to simplify grading, an answer sheet is provided to the students (see the supporting information). The sequential order of the chemical questions the students will encounter are generalized into nine question categories (shown in the rectangles) and the means by which the chemical questions are answered (shown in the ovals) are represented in Figure 1. The entire QDLE prelaboratory, laboratory, and postlaboratory exercise can readily be completed in a single, 3-h time frame.1 During the three hours, the students read the QDLE written treatment, perform the experiment, interpret all the data, answer the 33 questions, and arrive at a conclusion as to which mechanism is more internally consistent with the data. In that same period, there is ample time for the instructor to facilitate the process with lecture and discussion. Given the unique nature of the QDLE, the length of the written exercise is somewhat longer than that for a typical experimental protocol, with a word count of 3800 versus an average of 2600 words as verified by the evaluation of 36 experiments drawn from three laboratory manuals (20-22).
additional student beta tested the laboratory protocol. The design of this overall protocol enables the students to either do the prelab before or during the 3-h experiment time. Ample time was available within these down periods (after steps 8 and 9 in the procedure; see the supporting information) for answering the questions. The time required to complete the entire exercise, including answering prelab questions and performing the experiment, took an average of 2.5 h.
Literature Cited
A unique pedagogical approach for an undergraduate laboratory exercise is presented here, termed the question-driven laboratory exercise, QDLE. This approach uses guided questions and provided data to introduce the thought process that research entails. The QDLE approach features student interpretation from multiple data sets to derive principles. The data sets are in the form of prelab data (provided), experimental data (obtained by the student), and provided postlab data. Specifically, the QDLE concept is illustrated here with a second-year-level organic chemistry experiment involving a green solvent modification of Grignard reagent formation and reactions. Here, the students are guided through the development and testing of the green modification, and then distinguish between two competing mechanisms based upon consistency with the interpretations from provided and student-obtained data.
1. Bondeson, S. R.; Brummer, J. G.; Wright, S. M. J. Chem. Educ. 2001, 78, 56–57. 2. Graham, K. J.; Skoglund, K.; Schaller, C. P.; Muldoon, W. P.; Klassen, J. B. J. Chem. Educ. 2000, 77, 396–397. 3. Hessley, R. K. J. Chem. Educ. 2000, 77, 202–203. 4. Gaddis, B. A.; Schoffstall, A. M. J. Chem. Educ. 2007, 84, 848–851. 5. Rosenberg, R. E. J. Chem. Educ. 2007, 84, 1474–1476. 6. Latimer, D. J. Chem. Educ. 2007, 84, 699–701. 7. Berg, M. A. G.; Pointer, R. D. J. Chem. Educ. 2007, 84, 483–484. 8. Martínez, M.; Muller, G.; Rocamora, M.; Rodríguez, C. J. Chem. Educ. 2007, 84, 485–488. 9. Mills, N. S.; Spence, J. D.; Bushey, M. M. J. Chem. Educ. 2005, 82, 1226–1228. 10. Baar, M. R.; Russell, C. E.; Wustholz, K. L. J. Chem. Educ. 2005, 82, 1057–1058. 11. Abhyankar, S. B.; Dust, J. M. J. Chem. Educ. 1992, 69, 76. 12. Silversmith, E. F. J. Chem. Educ. 1991, 68, 688. 13. Kulp, S. S.; DiConcetto, J. A. J. Chem. Educ. 1990, 67, 271–273. 14. Orchin, M. J. Chem. Educ. 1989, 66, 586–588. 15. Williamson, K. L. J. Chem. Educ. 1988, 65, 376. 16. Nelson, D. J.; DiFrancesco, R.; Petters, D.; Nelson, D. J.; DiFrancesco, R.; Petters, D.; Einterz, R. M.; Ponder, J. W.; Lenox, R. S. J. Chem. Educ. 1977, 54, 382–383. 17. Duty, R. C.; Ryder, B. L. J. Chem. Educ. 1976, 53, 457–459. 18. Ziegler, G. R. J. Chem. Educ. 1967, 44, 609. 19. Lewis, H. F. J. Chem. Educ. 1930, 7, 856–858. 20. Lehman, J. W. Microscale Operational Organic Chemistry; Prentice Hall, Upper Saddle River, NJ, 2004. 21. CER. Organic Chemistry; Chem 303/304. Thomson Brooks/Cole: Belmont, CA, 2007; ISBN 13 978-0-495-14676-6. 22. Nimitz, J. S. Experiments in Organic Chemistry; Prentice Hall: Englewood Cliffs, NJ, 1991.
Notes
Supporting Information Available
Hazards All reagents in this experiment are flammable; thus, there should be no open flames during the procedure. Gloves and goggles should be worn as all reagents are also possible irritants and HCl is corrosive. All reagents should be dispensed from a hood. Conclusion
1. This QDLE was beta tested by four students under the direction of one of the authors (J.M.T.). Three students answered the guided questions unaided by an instructor. An
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Instructor's guide; instructor's answer key; student guide; student answer sheet. This material is available via the Internet at http://pubs. acs.org.
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