In the Classroom edited by
Second-Year and AP Chemistry
John Fischer Ashwaubenon High School Green Bay, WI 54304-5093
Process Development in the Teaching Laboratory Leonard C. Klein Central Shenandoah Valley Regional Governor’s School for Science and Technology, Fishersville, VA 22939 Susanne M. Dana* Roanoke Valley Governor’s School of Science and Technology, 2104 Grandin Rd., Roanoke, VA 24015
Many traditional high school and undergraduate laboratory exercises for synthesis are simple cookbook exercises meant to introduce students to new techniques. While this is a necessary and valuable experience for the student, laboratory experience can and should do much more than teach technique. In recent years, there has been exploration of the guided inquiry approach, where students discover concepts through experimentation and analysis of pooled data. The faculty at Holy Cross has developed a general and organic/ biophysical chemistry curriculum that allows students to discover concepts such as stoichiometric relation of reactants to products, thermochemistry, the Beer–Lambert law, and UV– vis transitions by experimenting and pooling data (1– 4 ). In their experience and ours, dividing a large experiment among students increases students’ accountability and responsibility for their work, yields much more complete and reliable data, and is a much more reliable and positive model for an industrial or academic scientist’s day-to-day work. One of the most important areas of industrial research is process development, or optimizing yield and purity of a reaction. The purpose of this article is to present a simple research project, appropriate for AP or second-year level chemistry students. Many lab manuals for high school and college chemistry courses contain an experiment for the preparation of aspirin (5, 6 ). These typically use 2–3 g of salicylic acid, 5–6 mL of acetic anhydride, and 5–10 drops of 85% phosphoric acid. This mixture is heated to 70–80 °C for 15 min and then the reaction is quenched. The product is recrystallized in an ethanol/water solution to increase purity. This provides students with a one- to two-period lab that introduces them to the synthetic process. In the present project, the reaction of study is optimized for both yield and purity with reference to unreacted salicylic acid. Outline of Project To introduce this lab sequence, students prepare a sample of aspirin as described in the lab manual. The material can be analyzed for purity through any of several methods (7–9). When Spectronic-20s are available, we have used them to quantitatively determine the percent of unreacted salicylic acid by formation of the purple iron(III) salicylic acid complex. If this equipment is not available, the standards can be compared to the sample visually for a rough determination of purity. Once the first sample has been prepared and analyzed, a class discussion is focused on the following questions: What are the variables in this procedure? How should the “best” method be defined? How can this problem be investigated?
It is hoped that from the class discussion students will identify the following as variables in the synthesis. 1. 2. 3. 4. 5. 6.
mass of salicylic acid volume of acetic anhydride temperature of the reaction time allowed for the reaction number of drops of catalyst use of acetic anhydride vs acetic acid
The class is divided into research teams and each team is assigned a variable to test. We normally suggest the amount of salicylic acid not be studied. This keeps all reactions on a constant scale and makes comparison easier. The teams are asked to draw up a research proposal that outlines how they will test their variable. Each team prepares at least 4 different samples of aspirin to compare with their “book prep”. It would be best if the students could repeat their sample preparations to verify consistency of method; however, this is not essential for this exercise, and often laboratory space and time are too limited for this. In the research proposal, students are guided on how to use each member most effectively. Since there are two or three members on each team, several samples can be prepared in one lab period with good planning of manpower and available space. Students find both the yield and purity of their products. With all their data in hand, the teams now present their result to the class. Using all the data from all the methods the class should discuss which method is “best”, using the definition of “best” arrived at in the start of the process. Students may need prodding to consider cost of materials, cost of heat, and cost of time in their decision of best method. Many times, consideration of these factors changes the students’ criteria for choosing the “best” method. The “best” method arrived at by the students is usually similar to the “book” method, especially with time and financial considerations (i.e., doubling the amount of time heated may increase the yield by 1%, but also doubles the cost of labor and energy). Finally the whole class uses the agreed-upon method to prepare one last sample set. The class can then compare their final product with the other samples prepared and the book method. Since students have prepared this compound several times by now, this last preparation provides an opportunity for evaluation of students’ lab technique. Discussion This research project does take a significant amount of laboratory and class time; we normally budget seven to ten hours of class time, with the understanding that much of the written work will be done at home. However, we have found
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In the Classroom
this to be an excellent springboard for review and discussion of many topics. Beyond introducing organic synthesis, this also can be used to review the relationship between the temperature of reaction and the rate of reaction, limiting reagents, Beer’s law, calculating yield and purity, metal complexes, and the concept of variables. We have used it most often at the end of a second-year high school chemistry course; it provides an interesting review of these principles for the Advanced Placement exam, or can be used after the exam is over as a closing exercise. We can be contacted at
[email protected] and
[email protected] for further information or questions. Acknowledgments This exercise was originally developed at New Horizons Governor’s School of Science and Technology. We gratefully acknowledge the contribution of the faculty, staff, and students
of NHGS, as well as our present employers, the Central Shenandoah Valley and Roanoke Valley Governor’s Schools. Literature Cited 1. Ricci, R. W.; Ditzler, M. A.; Jarret, R.; McMaster, P.; Herrick, R. J. Chem. Educ. 1994, 71, 404. 2. Ditzler, M. A., Ricci, R. W. J. Chem. Educ. 1994, 71, 685. 3. Ricci, R. W.; Ditzler, M. A.; Nestor, L. P. J. Chem. Educ. 1994, 71, 983. 4. Ricci, R. W.; Ditzler, M. A.; Jarret, R.; McMaster, P.; Herrick, R. J. Chem. Educ. 1991, 68, 228. 5. Hall, J. F. Experimental Chemistry, 2nd ed.; Heath: Lexington, MA, 1989; pp 486–488. 6. Parry, R. W.; Merrill, P.; Bassow, H. Chemistry: Experimental Foundations; Prentice-Hall: Englewood Cliffs, NJ, 1987; pp 92–94. 7. Street, K. W. J. Chem. Educ. 1988, 65, 914–915. 8. Braun, R. D. J. Chem. Educ. 1985, 62, 811–813. 9. Hall, J. F. Experimental Chemistry, 2nd ed.; Heath: Lexington, MA, 1989; p 490.
A Note from John Fischer, Editor of Second-Year and AP Chemistry The other day while I was talking to our new chemistry teacher, he mentioned that he was worried that he wasn’t doing a good job. He said he was teaching all of the proper content, and the kids were learning it, but his problem was that he felt his teaching was not much fun. When I asked him to elaborate, he explained that he went into the chemistry field because he enjoyed it in high school, because it was a fun class. His concern got the wheels turning in my head. That was the point I wanted to address. What can be done to make our second-year high school chemistry courses “fun”? I think this is a very important consideration, but the term fun needs to be defined. Fun does not necessarily mean lots of demonstrations, explosions, and no homework! Fun in chemistry means many things: interesting investigations, thought-provoking problems, learnercentered activities, open-ended questions, nontraditional experiments, group problem solving, and utilization of new technology, to name a few. In my advanced chemistry class, I have set up a program where my students simulate real research. They are divided into teams and are assigned a variety of nontraditional activities intended to simulate research. The first few activities are assigned by me, but I soon give the teams themselves the option of designing their own ideas. Some of the topics I assign are determining the percent methanol in a brand of windshield washer fluid, determining the molarity of a brand of drain cleaner, identifying the main ingredient in windshield washer gel. Once the students are comfortable with this type of problem solving, they suggest investigations such as Do all flavors of a given soda have the same pH? What makes invisible ink work? The goal is to get students to work together as teammates, to expose them to the fun as well as the frustration of research, and to provide them with higher-level problem solving. This kind of fun can really stimulate your students to apply themselves in your class, and by helping select the topics, you can insure that your students will be challenged as well. Making your class interesting does not have to mean “watering it down”, or playing demos, or cutting out important content because it is boring. Rather, it means teachers need to find ways to make their classes more interesting for students by rethinking the curriculum, implementing new technology, and finding ways to challenge students to apply themselves to the material that they are learning. Even with the constraint of an externally imposed curriculum, Advance Placement teachers have shared ideas to make boring topics more lively by being creative and innovative. It can be done, but it can be difficult if you aren’t the creative type. That is why I am challenging those who have made these kinds of changes to step forward and share their ideas. What can a second-year high school chemistry teacher do to make his or her class more appealing to students? My goal is to get teachers to share their innovations with others. If you have successful practices that could help other teachers improve their classes, please submit them to the Journal and we will focus this column on sharing the best of your ideas with your peers, to make chemistry fun for all. If you don’t have time to prepare a manuscript but you have an idea you would like to share in brief form, send it directly to me and it may be possible to combine several ideas into a “Second Year and AP Chemistry” column. Also, if you are looking for an idea to fit a particular topic, let me know and I’ll encourage others to submit ideas in response. I am excited about receiving your ideas and suggestions. John Fischer earned his Bachelor’s degree from Michigan Technological University in Houghton, Michigan, in 1979. He received his Master’s degree from Michigan State University in 1985. He is certified in chemistry, physics, and mathematics, and has been teaching 19 years at the high school level. He currently teaches chemistry, second-year chemistry, and physics at Ashwaubenon High School in Ashwaubenon, Wisconsin, a suburb of Green Bay. He is a member of the National Science Teachers Association, the Wisconsin Society of Science Teachers, and the Wisconsin Math Council. John Fischer • Ashwaubenon High School, 2391 Ridge Road, Green Bay, WI 54304 • email:
[email protected] 746
Journal of Chemical Education • Vol. 75 No. 6 June 1998 • JChemEd.chem.wisc.edu
