In the Classroom edited by
view from my classroom
David L. Byrum Flowing Wells High School Tuscon, AZ 85716
On Laboratory Work David Olney P. O. Box 559, Mattapoisett, MA 02739 As a longtime teacher at the high school level, I’ve observed many a swing of the educational pendulum. But one constant has been the use of student experimentation as a valuable learning tool. Like most teachers, I have a few “pet” labs that I’ve done for many years, because they work so well. There are others that I try, modify, and drop after a while. I should like this essay to comment on a few aspects of lab work in the typical college-prep class, based on my observations over the years. I will not attempt to systematically critique this area or report on the “state of the art”, but rather discuss some strategies I’ve used to get students more directly involved in the process of laboratory work— with examples. Too few of the labs in current manuals seem to require students to attempt designing procedures that can be used to answer a specific question. These kinds of labs are often referred to as “discovery” or “inquiry” labs, one of the focal points of the curricular reform movement of the 1960s. While “discovery” labs have much merit, they take time and one must be willing to omit something in the curriculum to provide it. In addition, the question to be explored must be sufficiently limited in scope and easy enough to investigate that students have a reasonable chance of designing and executing a proper experimental procedure. Here are some thoughts on maximizing student performance in this area. Don’t Be Afraid To Write Your Own Material I rarely use an instruction sheet straight from some manual. I find I want to modify instructions a bit, or to emphasize a different point. Thus virtually every work/instruction sheet I issue is my own. Here’s an example. The classic CHEM STUDY lab uses the Mg–HCl reaction to collect hydrogen gas. The purpose of the original lab was to “discover” the molar volume of this gas at STP. But to do so, students must know about gas law corrections and (it is hoped!) how to handle the vapor pressure of the water vapor present. By that point in the school year, my students have long since learned about 22.4 liters/mole at STP. Thus I change the purpose of the lab. The students carefully measure the length of their strip of magnesium, but may not mass out the sample. Instead, they must use their data to calculate the number of moles at work and to predict the mass of a 1.0-m strip from the roll used in today’s lab. And there’s extra credit if they are the team that gets closest to the actual value, measured with great flair at experiment’s end! New teachers should not be overwhelmed by the prospect of such rewriting. My one-page instruction sheet for this lab evolved over the years; and one of the glories of word-processing is to easily create new versions, when some new wrinkle does not work out in practice. Roger Plumsky’s article on Transmuted Labs in a recent issue of this Journal can provide more ideas on modifying familiar labs to better fit one’s purpose (1). Another advantage of writing one’s own material is
that one can modify or even eliminate “canned” data tables that guide students step-by-step through needed calculations. It would seem more logical to let students figure such things out as part of the problem-solving strategy posed by the purpose. Granted that canned tables speed up the process of correcting lab reports, and so may be a necessary evil; but something educationally useful is lost in the process if students do not have to organize their thoughts and data. Utilize the Unique Features of Microscale Labs The use of microscale equipment often lends itself to discovery exercises, since repeated trials can be done quickly, exploring systematic variation. As an example, many of us use the classic iodine clock reaction to start the introduction to collision theory and kinetics, so students can “discover” the effect of changing temperature and concentration on reaction time. However, I use a mix of techniques: macroscale work (4 mL or so in test tubes) to test temperature variations, but microscale work to display concentration effects. That’s been true since I first saw Bob Becker put two 1 × 10 well-plates mouth-to-mouth to get five different systems of solutions A and B to mix simultaneously— all within one minute. Try that macroscale! Throughout my teaching career I’ve used a “semimicro” setup involving equipment such as glass dropping bottles, small test tubes, and 50-mL beakers. Over the years I’ve prepared classroom sets of many reagents in dropping bottles, which a lab team takes to their desk in small racks. (Since I’ve taught mostly in “general purpose” science rooms, with no set lab stations as such, that’s been a necessity.) So when introduced to the magical world of Beral pipets, wellplates, and Petri dishes at the 1987 Dreyfus–Woodrow Wilson Foundation Institute at Princeton, I was an instant convert. We were inspired by Steve Thompson and Ed Waterman’s work in Colorado, as well as by Tom Russo and Ed Brogie. I wish I could claim to be unusually creative in adapting such equipment, as so many participants there were. But alas, my microscale labs are pretty prosaic, I fear. This past year about 50% of my labs used semimicro, the rest microscale. The best of them are not simply scaleddown versions of classic procedures, but rather utilize microscale’s special features. One such area is generation of “dangerous” chemicals in such small amounts as to be reasonable and safe. As an example, I have students late in the school year explore a copper–nitric acid system carried out within a closed well-plate or small test tube so that use of a fume hood is not required (there’s none in my room!)— yet the products of the redox can be easily identified. An excellent resource in this area is Chemtrek, Steve Thompson’s manual (2). It is a gold mine for ideas, especially for getting environmental chemistry into the day-today curriculum through lab work.
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In the Classroom Occasionally Have Students Carry Out Experimental Design In the sixties I was offered the chance to teach an AP chem course in New Rochelle, and I surveyed many collegelevel lab manuals. None were really suitable to a high school where one had at most a 90-minute lab period and limited equipment. But then I came across a manual so extraordinary that to this day I use its design 3 or 4 times a year. The manual is long out of print, and quite different in structure, so I shall describe it in some detail. Practice in Thinking, by Jay Young (3) For a particular topic the manual would present 10 “situations”. Here’s a sample from the section on Gas Behavior. Fill a test tube with hydrogen chloride. Close the mouth of the test tube with a stopper and place the closed mouth of the test tube under water. Remove the stopper. Why did the test tube fill with water?
The student team would (i) carry out the procedure (note the lack of explicit directions); (ii) create a hypothesis for their observation (often by consulting a variety of texts and other lab manuals); and then (iii) carry out an experiment that would tend to either confirm or deny their hypothesis. Having it be denied was perfectly OK, as long as the test was well designed. Each team did its own project. And so it went for about 18 topics, from Physical Changes to Oxidation–Reduction and on to Chemistry of Surfaces, Colloids, and Diffusion. Before all this, the manual discussed in detail the strategies involved in hypothesis testing and gave hints on lab procedures such as using burners, handling gases, and filtration, which students did as necessary based on their previous preparation. At the manual’s end were appendices on safety, writing good reports, serendipity in the lab, the responsibilities of the chemist (!), etc—all written in Jay’s down-toearth and nonpedantic style. It’s hard to imagine such a manual making it through the corporate world of the big publishing houses today. High school usage has prompted some modifications. On a given topic I might present perhaps 6 or 7 statements. The student’s job is to create an experimental test of that claim that tends either to confirm or to deny its validity. A team will be asked to test 4 or 5 statements during the lab period and is encouraged to compare notes with other teams after they’re done. The lab report is a concise, well-written paragraph for each claim tested, presenting what the team did, a short data table if appropriate, and their conclusion. It’s not too time-consuming to read, but students have to use a well-constructed English sentence or two to get their point across. For example, one of the first lab exercises in September is to “play” with microscale equipment. About the only chemical they use is water with a few drops of food coloring in it. Here are two of the several claims they might explore in this area: 1. The size of the drops released by a thin-stem pipet changes as the angle of the stem from vertical is changed, all else remaining the same. 2. It is impossible to get a liquid to fill the bulb of a thin-stem pipet more than 90% full by “squeezing” the bulb.
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(Many a smart kid has confidently explained to me why the latter is impossible based on principles of physics and air pressure and such, only to be shown by a supposedly “dumber” but creative peer a bulb quite full of colored water.) Note that the teacher does not autocratically state the dos and don’ts, or what the expected result is; nor does he or she dictate a set procedure. Some students will test claim #1 by massing, say, 20 drops delivered at various angles; others will measure the volume of 25 drops in a graduated cylinder; still others will count how many drops it takes to fill one well in a well-plate. The test designed need not be exhaustive, but should control variables as well as possible. Students might easily predict what will happen (and are encouraged to do so), but that’s not good enough; they must actually test it. And note that different teams might come to different conclusions—and both be “right” ! Again, perhaps once in each marking period, I have them do such a lab, be it on density or redox ideas, or acids/ bases/pH, or…. A creative teacher can easily create a series of claims on such topics, and the students get to do some real experimenting/hypothesis-testing, rather than following cut-and-dried recipes. Readers are urged to consider adapting it every once in a while. And if you ever come across a copy of Practice in Thinking, treasure it! Have the Computer Play a Role in Lab Work The what-if computer simulation can be a powerful educational tool. In this, the student inputs needed variables (from reasonable ranges) and quickly gets an outcome reported, without explanation. Repeated trials are easily accomplished, and systematic variation of one variable at a time is encouraged. For example, I wrote a BASIC program in 1987 called the Magical Mystical Ideal Gas Piston Machine Experiment to introduce gas law relationships. Real-life experiments on gases too often fail to truly generate the direct or inverse relationships we want students to sense intuitively. With the program, the relationships jump out from the data as students choose which variables to manipulate from among moles of sample, volume, pressure, and temperature (and, just as important, which to hold constant). Screen graphics show the piston at work, to visually reinforce the trends being observed. The program’s title was deliberately chosen to convey the idealized situation at hand; a good post-lab discussion can introduce ideas about experimental design, codifying results in algorithms, and ideal gas properties. Some will argue that what’s taking place is not truly lab work, and therefore it’s not suitable for this essay. But if we want to think about science education in the 21st century—education that reflects the real world of science and research techniques—I suspect we’ll have students learning to cope with automated, sophisticated, computer-driven equipment as the tool of choice. We should give students an occasional glimpse of what it’s about. Linking computers to laboratory work is not unreasonable. High school teachers have been using real-time lab interface devices connected to Apples for quite some time. One of the more promising new developments is connecting interface devices to powerful graphing calculators. The trick at the high-school level is to find suitable pedagogically sound situations to utilize them. The folks at Vernier Software have provided lots of ideas on using CBL instruments creatively (4).
Journal of Chemical Education • Vol. 74 No. 11 November 1997
In the Classroom Conclusion
Literature Cited
The common thread here is encourage students to think actively about how the question or hypothesis at hand might be explored systematically and to analyze the data collected in meaningful ways. Following cut-and-dried lab procedures minimizes student involvement and may prove so boring as to be counterproductive in the long run. The time it takes teachers to develop or find such materials is well worth the investment.
1. Plumsky, R. J. Chem Educ. 1996, 73, 451–454. 2. Thompson, S. Chemtrek: Small Scale Experiments for General Chemistry; Prentice Hall: Englewood Cliffs, NJ, 1989. 3. Young, J. Practice in Thinking; Prentice-Hall: Englewood Cliffs, NJ, 1958. 4. Holmquist, D.; Randall, J.; Volz, D. L. Chemistry with CBL Labs, v. 2; Vernier Software, 8565 S.W. Beaverton-Hillsdale Hwy, Portland, OR 97225-2429, 1997.
Dave Olney began his high school teaching career in 1958, the year following Sputnik. He taught at New Rochelle H.S. (NY) until 1973, then at Lexington H.S. (MA) from 1973 to his retirement in June 1996. A longtime “puzzle nut”, he became intrigued with computer programing and usage in the Chemistry/Physics classroom when PCs became common around 1970. This led to involvement with the chemistry summer institutes held at Princeton University under the aegis of the Woodrow Wilson Foundation from 1982 to 1992. He served as the director of computer activities under a variety of distinguished academic directors. He also was active in Project SERAPHIM, enjoying a one-semester sabbatical leave with the project as a Fellow in 1986. His computer programs have been widely shared, and he has contributed articles to the CHED newsletter on an ongoing basis over the years. Other articles have been published in this Journal, The Science Teacher, NEACT Journal, and CHEM 13 News among others. Like many of his vintage, he was the beneficiary of a host of Summer Institutes and Academic Year programs sponsored by NSF in the sixties and seventies, and has been active in workshop presentations at the regional and national level since. Awards include the Presidential Award winner for Massachusetts (1985) , Tandy Scholar Finalist (1990), a Regional Catalyst Award winner (1985), and the Northeast Region nominee for the Conant Award from ACS (1992). But his best reward has been the friendships made with Chemistry teachers around the country at both the high school and college level through the above programs. He can be reached at P.O. Box 559, Mattapoisett, MA 02739, or by email:
[email protected].
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