Secondary School Feature Articles

* The Chemistry behind Carbonless Copy Paper, by Mary Ann White, p 1119.

* Kids in a Candy Store: An Analogy for Back Titration, by Arthur M. Last, p 1121.

The Twenty-Fifth Column

This is the twenty-fifth "Especially for High School Chemistry Teachers" column. Special thanks are in order to each individual who has authored or reviewed a Secondary School Chemistry article during the past two years. Thank you also for the many suggestions received by correspondence, telephone conversation, and in person. In the table of contents each month several articles are marked with the * logo, indicating that the article is likely to be of interest to high school teachers. Your feedback on how well the marked articles fit your interests and needs is welcome; such "reality checks" are helpful in making the designations useful to as many readers as possible. It is impossible however, to pick a set of articles that fits every reader so please read "In This Issue" and scan the entire table of contents.

Misrepresentations and Misconceptions

As chemistry teachers we are continually faced with the misconceptions that students bring to our classes and with the misrepresentations that are found in textbooks. On many occasions during a career of teaching I have made matters worse through incomplete explanations and failing to adequately probe a student's understanding of a concept. Like many others, I have repeated misrepresentations taken directly from textbooks, usually in the form of oversimplified explanations. The Journal of Chemical Education has been a great source of articles that call attention to these errors. This issue contains useful articles on specific misconceptions and misrepresentations authored by William Robinson (p 1074) and Stephen Hawkes (p 1179), respectively. These two articles also serve as a reminder that there is a great deal of accessible information to help us identify and correct these difficulties.

Misconceptions

In his article Robinson discusses a group of misconceptions related to chemical bonding. He provides also a WWW address for the Educational Resources Information Center (ERIC) database. Following his suggestion of searching "chemistry AND misconception" yielded 115 citations from the past nine years. Among the topics mentioned in the 115 citations were misconceptions dealing with acids and bases, covalent bonding, structure, gases, chemical equilibrium, mole concept, dissolving and solution, and electrochemical and electrolytic cells. A number of the items cited are articles from readily accessible sources such as JCE. Several citations are from ChemSource (1), a resource which many teachers already have at their desk but perhaps do not think to check when planning or revising a unit. Taking a few minutes to consider what others have discovered through lengthy research may save a great deal of time and frustration for us now and, most importantly, for our students in the future.

Misrepresentations

Over the past several years, Stephen Hawkes has called to our attention misrepresentations that are perpetuated in textbooks and other teaching resources. Often the misrepresentation results from using a mathematical equation that is true only under very specific conditions. In the article in this issue Hawkes explains why calculating solubility from published K_sp values seldom leads to agreement with measured solubility values. If you do not teach AP chemistry, and do not include K_sp in an honors course, this example may not be relevant, but in previous articles he has pointed out similar difficulties with other topics. In many cases the focus in the textbook is on using a mathematical expression to calculate a value that is valid only in very limited circumstances. These articles remind us of the value of emphasizing conceptual understanding over often mindless mathematical manipulation. Several titles, each of which describes the contents of the article, are repeated here as a ready reference to common misrepresentations: "All Positive Ions Give Acid Solutions in Water" (2); "Salts Are Mostly NOT Ionized" (3); "pK_w Is Almost Never 14.0" (4); "Teaching the Truth about pH" (5); "Arrhenius Confuses Students"(6); "Graham's Law and Perpetuation of Error"(7); and "What Is a 'Heavy Metal?'"(8). A few minutes spent reviewing an applicable article before beginning a unit can be time well spent. A good example to consider is the notion that the value of K_w is 1. x 10¹⁴. Hawkes made the point (4) that plugging values into equations is easy, but ensuring that the equation is understood is much more of a challenge for both teacher and student. He suggested requiring explanations, such as "Give the chemical (not algebraic) reason that [H⁺] increases as [OH^-] decreases" and "K_w is the equilibrium constant of what reaction?"

Literature Cited

1. ChemSource SourceBook, Version 2.0; Orna, M. V., et al., Eds.; American Chemical Society Education Division: Washington DC, 1994; for information call 1-800-227-5558, ext. 2113.

2. Hawkes, S. J. J. Chem. Educ. 1996, 73, 516.

3. Hawkes, S. J. J. Chem. Educ. 1996, 73, 421.

4. Hawkes, S. J. J. Chem. Educ. 1995, 72, 799.

5. Hawkes, S. J. J. Chem. Educ. 1994, 71, 747.

6. Hawkes, S. J. J. Chem. Educ. 1992, 69, 542.

7. Hawkes, S. J. J. Chem. Educ. 1997, 74, 1069.

8. Hawkes, S. J. J. Chem. Educ. 1997, 74, 1374.