Chemical Education Today
Letters Solubility and the Perpetuation of Error The inadequacy of college education in chemistry is illustrated by an article in this Journal (1). The authors determine the solubility product of lead iodide assuming that it is totally dissociated in solution. In reality, the composition of the saturated solution is [Pb2+] = 1.35 × 10{3, [PbI+] = 0.31 × 10 {3, [PbI2 ] = 0.01 × 10{3 (calculated from data in the NIST collection [2]), yielding an error of nearly 20%. The authors could have learned this error from me in my first two decades of teaching. It is a bitter truth that we hand on errors from generation to generation and our profession has no mechanism to correct them. Professional research projects are based on fallacy as a result of our teaching. Literature Cited 1. Green, D. B.; Rechtsteiner, G.; Honodel, A. J. Chem. Educ. 1996, 73, 789–792. 2. Smith, R. M.; Martell, A. E.; Motekaitis, R. J. NIST Critical Stability Constants of Metal Complexes Database, Version 1, NIST Standard Reference Database 46; U.S. Department of Commerce, National Institute of Standards and Technology: Gaithersburg, MD. Stephen J. Hawkes Oregon State University Covallis, OR 97331-4003
* We do make the assumption of no ion pairing in solution, as Hawkes points out. In fact, we addressed, albeit only briefly, that an error introduced by ion pairing exists in this system. The reported values of K°sp obtained by the students are about 20–25% from the literature value. Students nearly always obtain a high result, which leads to lecture discussion of errors due to ion association when performing calculations involving solubility. David B. Green Natural Science Division Pepperdine University Malibu, CA 90263
* Has Chemical Education Reached Equilibrium? Your piece on the possible equilibrium nature of education is most thoughtful and (should be) provocative ( J. Chem. Educ. 1997, 74, 613). I think your editorial should be used as a rallying cry for a CHED symposium on ideas for, well, increasing the value of K eq. A plethora of papers has been presented over the years showing how novel teaching has been implemented, but not many really address the basic question of shifting responsibility to the learner. In my last several years of teaching I came to realize how minimal my teaching effort (which was enormous, from my viewpoint) was, compared to the importance of student initiative in their own learning. KinWORKS (Ramette, R. W. J. Chem. Educ. Software 1993, 6B, No. 2) and REACT (Ramette, R. W. J. Chem. Educ. Soft138
ware 1995, 8B, No. 1) aimed at helping students to ask the questions and find the answers themselves. The problem becomes overwhelming, I think, when one has to deal with a large class of students who are variously motivated. You can’t tell them to sink or swim in today’s world. But perhaps materials could be produced that would enable a self-selected subset of students to emphasize learning rather than assimilation. Beginning with my high school geometry class, which was the first time I actually felt myself using my mind to wrestle with questions that had no pat answer; later with an inexplicable desire to master complex equilibrium calculations beyond those in the text; then struggling with my thesis research; still later during the writing of my textbook—such experiences convinced me that learning is a do-it-yourself activity. As crusty Andy Rooney once put it: “We don't need better teachers—we need better students.” Richard W. Ramette Department of Chemistry Carleton College Northfield, MN 55057
* In regard to your June editorial in JCE concerning the state of chemical education, equilibrium and the LeChâtelier principle: a wonderful analogy. Perhaps this analogy can be expanded upon. An equilibrium system is one that is closed; hopefully the chemical curriculum (textbook content, etc.) is not—there is a net movement to someplace else. For instance in a metabolic pathway, a classic nonequilibrium system, in which LeChâtelier arguments can (nonetheless) be used effectively, there is a movement of metabolites from substrates to final products. This movement is both “pushed” and “pulled” forward. To continue the analogy, some things are added, some things are removed. Although chemistry as practiced has had a real change in the recent past, chemistry as taught (curriculum, textbooks, etc.) has lagged behind. The content of C&E News reflects the state of the chemical enterprise. I’ve been doing an informal survey of this content over the last several years. Here’s the movement. Articles: to biology and materials related, away from “traditional” areas. Job openings (academic, government, and industrial): to positions that are “nonchemical” (molecular biology, etc.), more interdisciplinary, or that are listed as “x” chemistry or related discipline (where x is a traditional subdiscipline), away from listings such as Ph.D. in organic chemistry. Advertisements: to ads for biotech, computational, and informational resources, away from industrial types of products. Titles of those doing the work reported in feature articles: professors of structural biology, molecular biology, biochemical engineering, materials science, physics, etc., away from only organic, physical, etc. chemistry. The way we assign names to departments and buildings says a lot: the Department of Chemistry and Chemical Biology at Harvard; the Chemical and Life Sciences Laboratory (at the University of Illinois, of which I am an alumnus). The driving force (the LeChâtelier effect) is already there—it is chemistry’s evolution from a discipline to a tool, and that tool is being used widely by lots of different stripes of scientists. Some years ago there was a PBS series hosted by Robert McNeil about the development of the English language. The central theme was that English became a wonderfully versatile language by being pretty darn indifferent to “dilution” by both other languages and idioms. Contrast this to the current effort in France to retain the purity of French from outside influences. As I see it this is the same
Journal of Chemical Education • Vol. 75 No. 2 February 1998 • JChemEd.chem.wisc.edu
Chemical Education Today
tension that is happening vis a vis the chemistry curriculum—the battle, although it is never framed in these terms, is between the “language” purists (keep the present content and maintain the integrity of the discipline = French) and the “language” innovators (change the content to reflect the changing nature of the discipline and how the discipline is used as a tool by others = English). I don’t so much worry about whether the curriculum will change—that is inevitable. I worry more about whom the curriculum will belong to! As chemical educators we must keep pace with the evolution of chemistry. To use another chemical analogy—the problem is not thermodynamics, it’s kinetics. This change has a really hefty negative free energy. The activation energy simply needs to be lowered by addition of catalyst. This catalysis, I believe, will occur in a twofold process: on the national level by a continuing well-reasoned advocacy for change and innovation; and institution by institution as newly trained multidisciplinary chemists come on line and, along with those already talking slang, start changing the language that everyone is speaking. Please don’t stop using the bully pulpit—those of us in the trenches need it! Emeric Schultz Department of Chemistry Bloomsburg University Bloomsburg, PA 17815
[email protected] *
It appears the problem is with the process our students go through in general. Our system allows too many mistakes to go by without being corrected. After all, a driving school would not let a driver pass with 30% errors. In the real world we keep on practicing until we get it right. Perhaps our culture is so imbued with competition that we assign too many problems at a time to students, so that mistakes are guaranteed in the first place. I would rather see a student get one problem right before going on to the next one, showing grasp of the concept. Eventually, if people are to be compared, a better basis is advancement in the subject—on what level that person solves a problem without error. A minimum level of advancement might have to be specified in the course, but students should be allowed to proceed as fast as they are able. It might mean more individual attention, which is to say, more money and prestige should be allocated to teaching. We had a graduate student who complained about the injustice of grading. She did not pass her written exam in her major. However, her professor allowed her to continue to work on research projects and she became “turned on” to a problem related to the complexing of Bi3+ with citrate. Even though the research went well she failed that exam three times; but the fourth time she finally got it right, and I mean, perfect. It took her seven years for her Master’s but when it came she deserved it. Frank Lornitzo Box 246 Route 5 Bradford, VT 05033
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Refrigerator Magnet Analogy I liked your JCE Activity #1 using the refrigerator magnet analogy ( J. Chem. Educ. 1997, 74, 1032A) and have shared it with our biology and physics faculty. My kids had fun with the magnet strip bouncing and my 12-year-old boy took it to school today to share with his friends. My 14-yearold girl, who doesn’t think she knows any science, picked up right away about the repelling and attracting, although we need to talk about charges vs magnetic fields. I don’t think you could ask for much better response than that. By the way, a cheap and easily obtained source of the magnets is an office supply house. Ours (Office Max) has business card magnets called “Magna Card”, which are designed to put your business cards on. Henry R. Derr Department of Chemistry Laramie County Community College Cheyenne, WY 82007-3299 email:
[email protected] * Easy Filling of a Buret Saqib Ali, M. Mazhar, and Khalid Mahmood ( J. Chem. Educ. 1993, 70, 169, Easy Filling of a Buret for a Number of Titrations) describe an apparatus to achieve this objective. The problem is how to construct it without more precise instructions. Boring a common buret and welding tubings (specially to the syringe and the buret) require considerable experience, and valves to insure that the solution does not flow back during titration are not always available and are hard to install. For those condemned to perform many routine titrations an arrangement such as that pictured here could be used. It is based on parts of broken burets tightly connected by tubings, having decided to fill the buret by the lower part (graduated tube (A), “T” tubing (B), stopcocks (C, D) and a flexible tubing (E) connecting the reservoir (F)). Francisco J. Arnáiz Departamento de Química Inorgánica Colegio Universitario de Burgos 09002 Burgos, Spain
*
Some Suggestions To Treat Sodium Wastes In J. Chem. Educ. 1993, 70, 408, a recovery procedure to save sodium and alcohol at the same time as reducing wastes has been described. In view of the growing importance of recycling and minimizing the production of wastes, here are some related procedures. 1. Using the metal as a fine wire (ca. 1 mm diameter) and benzophenone as indicator, under an inert atmosphere, the sodium is almost completely consumed. Thus, cuttings from lumps may become the most important source of sodium residues. However, since sodium wire is not required to purify other common solvents such as highboiling petroleum, toluene, xylenes, 1,4-dioxane, and some tertiary amines, cuttings may be destined to this purpose. These solvents consume almost all sodium (the unreacted metal, which forms shiny drops into the refluxing solvent, remains sufficiently separated from the “hydroxide” in the cold solvent so that at the moment of cleaning the flask most metal can be recovered and recycled). 2. Ethanol is the alcohol of choice in many labs to destroy sodium wastes. However, of all chemicals able to achieve this operation, 2-propanol deserves special attention. It reacts with sodium more smoothly than the lower alcohols methanol and ethanol (the first is inadvisable for inexperienced students because it is too reactive, flammability and toxicity apart); it is cheaper than ethanol (even considering its higher molecular weight); and it is miscible with most solvents, which enables mixing it with water to speed some reactions (adding an isopropanol–water mixture to the reacting isopropanol is more advisable), or with petroleum to smooth others (the suspected highly reacted waste is covered with petroleum and then the isopropanol is added). 3. For those using ethanol who want to conserve it as much as possible, the following procedure is suggested. Suppose a 2-L flask has been charged with 40–50 g of sodium to dry a solvent. To clean the flask, the solvent is decanted (or filtered) to another similar dry flask which is recharged. The flask containing the waste is treated with 1 L of 96% ethanol (or denatured ethanol). When hydrogen evolution ceases, 50 mL of water and 150 g of NaHCO3 are added consecutively and the flask is left to stand stoppered in the hood until the next operation of cleaning, for which the supernatant impure ethanol is used. The reactions taking place in the flask, in a simplified manner, can be written as follows: Na + H2 O (accompanying EtOH) = NaOH + 1/2 H2 Na + EtOH = NaOEt + 1/2 H 2 NaOEt + H 2O = NaOH + EtOH NaOH + NaHCO3 = Na2 CO3 + H 2 O Na 2CO 3 + x H2 O = Na 2CO 3?x H2O
(1) (2) (3) (4) (5)
The procedure is based on the following considerations. About 2 mol of sodium is initially used, so less than 2 mol of water (present in the 96% ethanol), or alcohol if denatured “anhydrous” ethanol is used, is required to react all sodium; 50 mL of water is sufficient to restore the ethanol. Approximately 150 g of NaHCO3 is required to transform 2 mol of NaOH into Na2CO3; NaHCO3 is soluble in water and insoluble in ethanol; the thermal effect associated with reaction 4, which is mainly diffusion controlled, is low. Na 2CO3 is a moderate dehydrating agent insoluble in ethanol, as are its hydrates, and reaction 5 also proceeds smoothly. Thus, the ethanol decanted from this mixture is ready to reuse (the presence of some NaOH in solution can be ignored) and the solid, consisting mainly
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Chemical Education Today
Letters of a mixture of Na2CO3 ?x H2 O and unreacted NaHCO3 impregnated with ethanol, is discarded or stored waiting for a destiny. 4. A suggestion to use for this waste. This material (preferably heated to 200 °C to transform the mixture into Na 2CO3) is appropriate for the preparation of Na 2CO3?10H2O, a convenient classical experiment for the freshman lab because (i) crystallization, as a technique of purification, is more significant starting from an impure product; (ii) data about solubility and stability of Na2CO3 hydrates are easily available from tables; (iii) Na2CO3 ?10H2O can be obtained as large, beautiful, clear, colorless crystals; (iv) it becomes superficially white very soon in air at room temperature, thus illustrating efflorescence and the associated crystal structure collapse; (v) the composition of partially dehydrated samples can be determined by weight difference after moderate heating; (vi) the product is adequate for acid–base titrations; and (vi) in case some student has not worked properly and an impure product is obtained (e.g., lower hydrates or sesquicarbonate also crystallizing), the interpretation of results from the above tests is straightforward. Other primary uses for this product are the neutralization of acid wastes, including escapes and spills, and the generation of CO2. Francisco J. Arnáiz Departamento de Química Inorgánica Colegio Universitario de Burgos 09002 Burgos, Spain
*
Glass Apparatus for Gas Generation Birk and Walters ( J. Chem. Educ. 1993, 70, 587) described a specially designed apparatus to measure the pressure of hydrogen gas in the magnesium–hydrochloric acid reaction (more precisely to generate hydrogen) in which the magnesium is placed onto the lip of a stopcock, so that by tipping the glass container the magnesium falls into the hydrochloric acid. Because the construction of such apparatus may discourage those interested in this experiment, I want to note that it may be similarly carried out by using a conventional arrangement for gas generation based on standard glassware (the solid into a bent tube is discharged by twisting it as required). However, since the bent tube involved is not a common piece in catalogs from suppliers, in case such a tube is not available, its equivalent, a drying tube tightly closed with a rubber stopper, may be used. The basic assembly is shown at right. Reducing the number of joints as much as possible is always advisable when a gas, and especially the elusive hydrogen, is involved. Thus, an assembly such as that depicted below seems to me more appropriate. Now the magnesium strip is folded over a magnetic stirring bar and added to the hydrochloric solution when required by means of a magnet. Francisco J. Arnáiz Departamento de Química Inorgánica Colegio Universitario de Burgos 09002 Burgos, Spain
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