Chapter 15
Reactivity Network Cooperation Between Academic Inorganic Chemists and High School Teachers
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Ε. K. Mellon and T. G. Berger Β. Department of Chemistry, The Florida State University, Tallahassee, FL 32306-3006 The aims of the Reactivity Network are to collect descriptions of chemical phenomena and suggest how these phenomena might be transformed into experimental problems for K-12 students. Network writing teams are made up of content experts and experienced teachers whose goal is to produce reviews to be published in the Journal of Chemical Education. The reviews will be reprinted and disseminated to chemistry teachers nationwide through a network of about 250 chemical educators at all levels from elementary through college. Use of local networks expands the reach of the Reactivity Network to thousands of teachers. These reviews stress descriptive chemistry, for example, reaction rates, driving forces, and catalysis in the context of student's everyday experiences. The Network examines alternate methods of presenting material which might pose waste disposal or health problems if performed in a traditional manner. Interesting examples of information gathered by the Network are presented. "...Scientists seldom invent a theory without having first an anomalous or puzzling event to explain. It seems odd to me that we should expect students to learn science without being puzzledfirst,or without even having asked a scientific question... " E. M . Vitz(ï) The idea for the REACTIVITY NETWORK^) began as early as 1978 at an international conference on introductory chemistry entitled "New Directions in the Chemistry Curriculum"(7) held at McMaster University. Participants in this Conference agreed that the general chemistry courses at both the high school and college levels are overloaded with theory. Worse still, this oversimplified theory is presented to an audience insufficiently mature to
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In Partnerships in Chemical Research and Education; McEvoy, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
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appreciate it. Participants proposed, rather, that beginning chemistry courses should contain an artftil blend of appropriate theory and the direct observation and interpretation of chemical phenomena. It would be best if these observed phenomena were concrete, and rooted in the student's everyday lives. For example, inorganic chemical reactivity (What reacts with what? How far? How fast?) is far under-represented in our beginning courses where the emphasis is on "...the uncomprehending memorization of over-simplified theories."(t) The REACTIVITY NETWORK was organized as one mechanism towards the reintroduction of chemical reactivity into beginning chemistry courses. The REACTIVITY NETWORK, directed by Ε. K. Mellon, began formally in early 1987 with a planning conference supported by the ACS Society Committee on Education. Support for this project by the NSF began in the summer of 1987. The NETWORK is dedicated to reducing the endless mass of inorganic chemical reactivity information in the chemical literature into a form usable by teachers, curriculum developers, and textbook authors. Inorganic chemical reactivity was chosen as the primary focus of the REACTIVITY NETWORK because it provides colorful, interesting phenomena with which to rivet student interest, and because it yields a rich bounty of experimental problems at all levels for students to solve. Network writing teams are comprised of content experts and experienced teachers whose goal is to produce reactivity reviews for publication in the Journal of Chemical Education. Simple reactions, driving forces, rates, catalysis and the manipulation of equilibrium states by temperature and concentration changes are stressed—all within the context of relating the reactions to student's everyday experiences. The reviews will be disseminated to chemistry teachers nationwide through a network of some 250 chemical educators recruited at all levels from elementary school through college. The high school teachers recruited for the Network have their own local teacher networks, so that the REACTIVITY NETWORK has the potential of reaching thousands of high school chemistry teachers. The first of the reviews is a survey of the reactivity literature dating to Michael Faraday in the 1820's.(3) The second by a team of Arizona teachers led by Jim Birk(4) encompasses the reactivity of nickel, and is typical of the reviews to come, spanning in student interest the middle school years through first year college chemistry. The third review, authored by a Georgia team led by Butch Atwood, addresses the difference between inorganic and nuclear reactivity, and the reason why entropy change is important in one domain and not the other.(5) This paper is intended for advanced placement or college students. The reviews will encourage the use of microscale manipulations since chemical safety and waste disposal are of such grave public concern. They will call for the use of equipment, such as chemical microscopes, already present in most schools and colleges but under-utilized in chemistry instruction. At the urging of the American Chemical Society Committee on Education, sensitive areas, such as chromium and nickel chemistry—where many school systems have banned these reagents altogether—will not be sidestepped. The more hazardous operations, which are clearly identified as such in the reviews, may well find their way into the high school laboratory by way of modern teaching technology, for example on videodisc ot videotape.-.. . . . . Λ
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The recent American Association for the Advancement of Science report Science For A l l Americans(e) calls (once again) for extensive reforms in our educational system, suggesting that when we teach for scientific literacy, the instruction, to be honest, must be consistent with scientific values and with the spirit and character of scientific research. Why stress the memorization of answers? Should we not stress the framing and answering of scientific questions, instead? Is not this the procedure we use in our research? Should not much of students' instructional time be spent on evidence collection, hypothesis generation and problem solving? Should we not reward curiosity and creativity instead of unquestioning memorization? Specifically, Science For A l l Americans^) reminds us that what the lecturer projects is not necessarily what the student learns. Meaning must be constructed in the mind by each student individually. Frequently, students must radically restructure thinking to banish misconceptions. This process requires working with concepts over time in a variety of situations, preferably problem solving ones. The REACTIVITY NETWORK reviews will collect descriptions of chemical phenomena and suggest how the phenomena might be transformed into experimental problems. Learning progresses from the concrete to the abstract. Perhaps our greatest fallacy is to mistake students' familiarity with jargon as true learning. Is is time to pare down the number of topics covered and emphasize only the more important. Quality learning is time consuming. A second major curriculum reform project coming on the scene is the National Science Teachers Association's "Scope, Sequence, and Coordination of Secondary Science" (SSC) project. It seeks to attack the problem of science illiteracy by having every student study science (no tracking) in grades 7-12. Chemistry instruction will be spread out over several years time, and will progress from the concrete to the abstract. The ACS white paper "Education Policies for National Survival(7) suggests that for grades K-8 we need "...the development of safe, hands-on laboratory experiences that present science as a problem-solving endeavor within a societal context..." Everyday common sense leads one to the conclusion that laboratory instruction should be dedicated in large part to the solution of experimental problems. Before true problems can be addressed, however, the interest of the student (and often, of the teacher) must be captured. The chemistry sets which made chemistry so attractive to youngsters in years past are now history. The REACTIVITY NETWORK Project will reintroduce many of those engaging chemical phenomena. Here are some interest capturers collected from the REACTIVITY NETWORK. The supplies are readily accessible and the procedures simple. Most chemists will be unable to resist trying them: ** Reversibility is demonstrated in this first example. Nickel(II) nitrate hexahydrate is placed in a cryophorus~a sealed tube(4,8) and thermally decomposed. If the container is allowed to sit undisturbed, the Νΐ(Ν0 ) ·6Η 0 is regenerated. 3
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Good demonstrations raise experimental questions. Can other metal nitrates be used? What about other hydrates? Are there cases where regeneration does not take place? What has happened to the metal ions in the cases where regeneration does not take place? PROCEDURE: Make a U-tube out of 8mm glass tubing and seal one end. Chase the moisture out of the tube with a flame or heat gun. Allow the tube to cool and add a few crystals of blue Νΐ(Ν0 ) ·6Η 0. Attach the open end to a water aspirator and evacuate. Seal the tube with a flame. Taking appropriate safety precautions, gently heat the nickel(II) nitrate crystals. The thermal decomposition produces black nickel(II) oxide in the tube, water vapor on the walls, and red gaseous N 0 . Blue crystals of the hydrated nickel(II) nitrate begin to reappear after a few hours. The nickel complex is observed to be fully regenerated in several days.(4) With care, this system can be reused many times, thus no waste is generated. 3
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** In this next relatively simple example mineral-like crystaline layers grow in a test tube. Water is added to a large test tube charged with iron nails and layers of salt and copper(II) sulfate. The nails are oxidized, while the copper ions are reduced to the metal. The products form in aerobic and anaerobic regions of the tube. A beautiful copper tree grows from the iron nails downwards into the salt layer. Although the first changes results are observable within a few minutes, the process develops over a period of months. It is rare that students encounter any system that takes more than an hour to reach equilibrium. It is best to leave the system undisturbed. Students can assemble and store the tubes at home because of the innocuous nature of the components. Will other metal-salt combinations work as well? Will such systems be speedier? Slower? What is the composition of each layer? Why does not the copper metal tarnish even after long periods of time? What is the role of the salt layer? What is the nature of the airtight plug? In the anaerobic portion of the system what is being organized into "mineral strata"? Do all iron-copper(II) sulfate tubes react at the same rate? Can the strata be separated for qualitative analysis? PROCEDURE: Add 1" of solid CuS0 «5H 0 to a large, dry test tube. Add a circular filter paper spacer. Now add 2" of iodide-free NaCl and another spacer on top. Place two or three ungalvanized iron nails on top of the second spacer. Carefully, add water to cover the nails (ensure there are no entrapped bubbles). Leave undisturbed and observe the changes. No special precautions with respect to waste disposal need to be taken with this experiment/demonstration. SUGGESTION: A rack may be built to hold a number of test tubes. Each year the students set up a fresh tube and compare it to the results observed in the previous years' experiments. As indicated previously, initial results are observable within a few minutes.(9) 4
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** This demonstration involves painting with compounds that change color when they are dried with a heat gun. It is a variation of the pink-
In Partnerships in Chemical Research and Education; McEvoy, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
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blue "disappearing ink" trick using hydrated/dehydrated cobalt(II) chloride. QUESTIONS: Why is there a change in color when the salts are dried? If they are allowed to reabsorb water, do they return to their initial colors? If shades of coloration are desired, which pigments should be applied first? Why will the paintings containing iodides yellow if allowed to remain hydrated? Does this also happen with the iron(III) chloride? What would happen if the paper is kept dry, in bottles, with a desiccant present? Can other metal salts be used for different colors? Will they also change color in time? Will different metals interact to yield results you would not expect? PROCEDURE: Dissolve mixtures of cobalt(II) chloride and various quantities of sodium or potassium bromide and iodide in water. Iron(III) chloride can also be used. Use a paint brush to make water color paintings on paper (filter paper works very well). With some experimentation, water color paintings which encompass a wide variety of colors (yellow, pink, green, blue) can be made which appear when heated and disappear in a humid atmosphere.(fO) These solutions can be kept for the next year, or, since they contain very little cobalt, disposal in the trash is appropriate. The salts can be washed off the paper and the cobalt recovered from the resulting solution. Most importantly, reactivity phenomena can form the bases for experimental problems. The fact that CuCl is a white, insoluble solid is certainly memorizable. How much more meaningful is this fact when it is the key to the solution of a problem: Place 1 cm pieces of bright copper wire in each of two small test tubes. To one tube add 0.5 mL of dilute CuCl and to the other add 0.5 mL of dilute CuS0 . The problem is to account for the difference - i n the tube where chloride is present, the copper corrodes away, and a white solid (CuCl) is formed. In the other tube the Cu remains bright. The formation of insoluble CuCl drives the corrosion reaction forward. Textbooks tell students that "ferrous hydroxide is a pale green solid." As Eugene Rochow pointed out during the 1978 McMaster Conference(e), the dry recital of memorized fact is what killed the "old" descriptive chemistry. Anyway, pure ferrous hydroxide is not pale green, it is white. But when one mixes ferrous and hydroxide ion solutions in the open air, the precipitated green ferrous hydroxide darkens rapidly to a black color, and eventually becomes the familiar red-orange hydrated ferric oxide. This phenomenon raises many questions, all answerable experimentally: *What causes the decolorization? *How would you make white Fe(OH) ? *Can you prevent (mask) ferric hydroxide precipitation by adding ligands known to complex the ferric ion? *Does the rate of air oxidation of ferrous ion vary with hydroxide ion concentration? This iron chemistry phenomenon can be related to day-to-day concerns: 2
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Why is window glass green when viewed edge on? What evidence do we have from iron chemistry concerning the oxygen content of the earth's prehistoric atmosphere? We can no longer consider the accurate transmission of content by lecture alone to constitute all that is required for effective chemistry teaching at the high school and grade school levels. The student market has moved in a different direction and we must alter our methods accordingly.
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Acknowledgment. The REACTIVITY NETWORK is sponsored by the U.S. National Science Foundation under Grant Number: M R 87-51183. Literature Cited. (1) Proceedings of an International Conference on Introductory Chemistry: New Directions in the Chemistry Curriculum: McMaster University: Hamilton, Ontario, Canada, 1978. (2) Mellon, E.K. SYNERGY, 1990, 4, No. 2, 6-7. (3) Mellon, E.K. J. Chem. Educ., 1989, 66, 251-256. (4) Birk, J.P.; Bennett, I., Boran, M., Kinney, C. J. Chem. Educ., 1991, 68, 48-54. (5) Godfrey, I; McLauchlan, R.; Atwood, C.H. J. Chem.Educ.,accepted for publication. (6) Science for All Americans: A Project 2061 Report: AAAS: Washington, D.C., 1989. (7) ACS White Paper: Education Policies for National Survival, November 14, 1989, American Chemical Society, 1155 Sixteenth Street, N.W., Washington, D.C. 20036. (8) Campbell, J.A. J. Chem. Educ., 1970, 47, 273-277. (9) Cortez, J.A.; Powell, D.; Mellon, E.K.J.Chem.Educ.,1988,65,350-351. (10) Bare, W.D.; Mellon, E.K. J. Chem.Educ.,submitted for publication. RECEIVED April 1, 1991
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