Environmental Chemistry in the High School Curriculum Camle Steams Horace Mann School, 231 W. 246th Street, Bronx, NY 10471

High school chemistry teachers are striving to make their courses more relevant to students' interests. In my chemis- trv class a t the Horace Mann School. this eoal is addressed h i incorporating environmental chemistryiopics in the tra- ditional high school curriculum. Environmental issues are among today's most important global problems, and many high school students are already aware of acid rain, melt- downs, and smog. Their concern, initially, may he political, hut it generates a curiosity for the scientific aspect of these issues.

All 10th graders a t Horace Mann take a year-long chemis- try course. Each class has a few students who will pursue science in college and also has students for whom high school chemistry will he their final science course. The environmen- tal topics have had broad appeal to both groups.

These topics provide a contemporary theme in an other- wise traditional course. The students' curiosity about acid rain motivates them to understand the oxidation states of sulfur and the real-life significance of the pH scale. Similar- ly, an investigation of the ozone layer encourages the stu- dents to study bond energies, gas behavior, and reaction kinetics. Many of my students approached chemistry as a collection of distinct subjects, each covered in a separate chapter. The environmental topics illustrate how areas of chemistry may he integrated in order to understand a real- world problem.

Classroom discussions of environmental issues are also an

Table 1. An Environmental Chemistry Lesson Plan: The Sulfur Cycle and Acld Raln

I. Descriptive chemistry of the environmentally important oxidation states of Sulfur

A. -2 oxidation state: H*S B. +4 oxidation state: SO2, H2S03, and suifites C. +6 oxidation state: SO3. H2S04. and sulfates

11. The biogeachemical sulfur cycle A. Background topics

1. Oxidation reduction reactions 2. Chemical properties of me nanmetais 3. Reaction kinetics

B. Enrichment topics 1. Chemical composition of seawater 2. Bacteria as chemical catalysts 3. Volcanoes 4. Chemical reactions in the atmosphere 5. Solar energy and photoinduced reactions

ill. Recant sources of environmental SO2 A. Fossil fuels B. Processing ores

IV. Acid Rain A. Background Topics

1. Acids and Bases 2. pH scale 3. Reaction kinetics

B. Oxidation of SO2 in the atmosphere C. Measuring acidity and evaluating the data D. Envimnmental impact of acid precipitation E. Controlling SO2 emission F. Enrichment topics

1. Buffers 2. Acids and the carbonate-bicarbonate equilibrium 3. Aquatic ecosystems 4. Weather patterns

important part of the course and relate science to social values and political action. Environmental topics receive excellent coveraee in the New York Times and the Wall - Street Journal, and articles from these newspapers are as- signed to s u ~ ~ l e m e n t our text and provide backaround for thkse discussibns.

- This paper will describe a few of the environmental topics

and labur&ory experiments that are popular with my sru- dents. Each of the topics crosses several traditional chapter headings and tries to unify the course content around~the environmental issue.

The Sulfur Cycle and Acld Raln Backeround tonics for the acid rain unit are developed

from th;! beginning of the course (see Table 1). The chemical reactions of hvdroeen sulfide. sulfur dioxide. and sulfur tri- - oxide provide examples in stbichiometry ca~culations, illus- trate Le Chatelier's principle, and appear again in evaluat- ing equilibrium-consiant eip;essions.-

- The acidic properties and solubilities of these compounds

and their chemical reactivities are covered as part of a dis- cussion of the chemistry of the nonmetals. A number of demonstrations are used to illustrate these reactions (1.2). A simplified diagram of the hiogeochemical sulfur cycle (see figure) shows the environmental processes that we study.

A simplified diagram of the biogeochemical sulfur cycle: Sulfur enters the atmosphere as H C , SOs and sulfate =Its from sea spray. Water droplets transport sulfuric acid and sulfate salts to the Earth's surface.

232 Journal of Chemical Education

Classroom discussion mentions the reduced forms of sulfur in living matter and the bacteria-induced reactions that oc- cur in the soil.

Industrial sources, mostly SO2 from the combustion of sulfur-containing fossil fuels, are responsible for about one- third of the sulfur in the cycle. The sources are in industrial- ized areas, but weather transport the sulfur oxides great distances.

The biogeochemical sulfur cycle summarizes the chemical precursors of acid rain. The students have little familiarity with reaction kinetics, and the discussion turns to factors such as moisture and sunlight that effect the rate of SO2 oxidation in the atmosohere. The oxidized product. S02, readily soluble in wate; droplets, forms a mist of sulfuric acid. Precipitation carries the acid mist back to the earth's surface.

The unit on acid deposition begins with a demonstration of the number of drops of dilute sulfuric acid required to change the pH of a liter of water from 7 to 6 then to 5 and to 4, emphasizing the logarithmic nature of the pH scale. We examine current data on the average pH of precipitation in the United States and observe the rate of reaction of the above solutions with small bits of calcium carbonate. Several effects of acid deposition are mentioned, such as disturbing freshwater ecosystems, defoliating trees, altering cation eauilibrium in soil, and dissolvina structural materials such asstone and marble.

- The choice of specific topics for classroom discussion de-

pends on the special interests of the students. The science- oriented students may want to investigate the kinetics of atmospheric oxidation of sulfur dioxide. The less science- minded students may he more interested in the effect of acid ~recioitation on the ancient architectural monuments of breece. Both groups have adequate chemical background for an intelligent discussion of acid precipitation. Selected newspaper articles, which are required reading, provide ad- ditional background for these discussions.

Radioactivity and Nuclear Energy ..

Nuclear properties and radioactive decay are included in our chemistry curriculum. The environmental issues associ- ated with this topic are of great concern to students today. Whether motivated by fear of survival in a nuclear age or curiosity about how a nuclear power plant works, students want to know more about radioactivity. This topic is iutro- duced with a discussion of decay modes and half-life (see Table 2). Sample mass-into-energy calculations begin to fa-

Table 2. An Environmental Chemistry Lesson Plan: Radloactlvity and Nuclear Energy

I. Radioactive decay and half-life A. Alpha, beta, and gamma decay B. Natural radioactive series C. Half-life calculations D. Conversion of mass to energy E. Binding energy

1 1 , Interaction of radiation with matter A. Energy loss through ionization 8. Ranges C. Radioactivity in the body

Ill. Radon A. A Contrast of chemical and nuclear properties 8 . Soil radon- health hazard

1. Sources of soil radon 2. Radon transport from the Soil 3. Radon and lung cancer

IV. Nuclear energy A. Fission and fusion 8. Solar energy C. Design of a nuclear power plant D. Fuel-SOU~CBS and disposal E. HOW safe?

miliarize the students with the magnitude of energy avail- able in nuclear reactions as compared to chemical reactions.

The behavior of alpha and beta particles and gamma rays as they pass through matter is discussed in some detail. Commercial low-level radioactive sources and a Geiger counter can be used to illustrate the differences in rangeiof alnhas. betas. and gammas. A source is mounted in front of a ~ e i ~ e r c o u n t e r window, and absorbers of different density and thickness are placed between source and detector. Stu- dents are amazed that alpha particles cannot penetrate a piece of paper, whereas gamma rays pass through a centime- ter of lead. They are also curious about the fate of the alpha particles. This leads to a discussion of the ionization pro- duced by high-energy alpha particles and emphasizes again the contrast between nuclear energies and chemical bond energies.

Radon pollution is an environmental topic that allows the students to review their understanding of alpha particles interacting with matter. Radium, present in the earth's crust, decays into radon. This chemically inert but radioac- tive gas diffuses to the surface with the other soil gases. Radon undergoes alpha decay, as does its daughter, poloni- um. If released into the atmosphere, the radon is not danger- ous, but it may he carried into the basements of buildings. Radon daughters may become attached to dust particles, which, in confined spaces, may be inhaled and lodge in the lungs. Thestudents are able tounderstand the health hazard of an alpha source inside the body.

Other nuclear chemistrv t o ~ i c s can he related to environ- mental issues. Fusion and fisHion are typical examples. The former includes a discussion of solar energy and a calculation of the amount of mass destroyed on the sun each hour. Fission leads into the environmental part of the unit, which starts with the fission process and the design of nuclear reactors. Following the Chernobyl disaster, newspaper arti- cles provided the technical background for discussions of air-borne radioactivity, the effect of radiation on the body, reactor shieldine. and nuclear waste disposal. -.

Other recent environmental topics in my chemistry course include the ozone shield. carbon dioxide in the atmosohere, and mineral resources. ~ o t all of these are covered-every vear: the selection is based on the students' interests and . . current news topics. A few minutes at the start of class may be sufficient to review a relevant article from yesterday's newspaper. However, a major atmospheric chemistry topic such as acid rain occupies several days of class time.

Resource materials-on environmintal issues suitable for high school chemistry teachers (see Appendix) come from reEent editions of college chemistry, physics, and environ- mental science texts and some current periodicals. The ref- erences have useful data and sueeest eood homework oroh- lems, but the actual class prese&tionmust he in the infor- mal, qualitative style of high school chemistry.

Environmental Chemistry Laboratow Experiments . .

A colleague' at a nearby university has developed a college course in environmental chemistry with a wealth of labora- tory activities that teach quantitative techniques while mak- ing measurements on air, soil, and water. We have modified several of these experiments to develop a program agpropri- ate to the high school chemistry lahorat~ry.~

Each experiment offers the following features:

(1) introduction to a general analytic procedure using standard laboratory glassware such as burets and flasks (a colorimeter is helpful but not necessary),

(2) analysis of familiar environmental or household materials, (3) stoichiometry calculations with environmentalsignificance, and (4) results that lead to interesting discussions in the classroom.

' Carlo Parravano, State University of New York, Purchase, NY. 2Copies of these experiments are available from the author.

Volume 65 Number 3 March 1988 233

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Ingeraoll, A. P.Sci .Am. 1983.249(3!, 162. Coruin, J.F. J. Chem.Educ. 1370.47.522.

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Wi1deman.T.R.. J. Chem. Educ 1974,51,290. Einenmann, M. A. J. Cham. Edur. 1980.57.897.

Wwdwel1,G.M Sci. Am. 1978.23811!,34. Feighan, J.A.;Rondini,J. A. J . Cham.Edue. 1384.61.740. Glover, I. T.: Johnson, F. T. J, Chem Educ. 1973,50,426. Navari. R. M. J. Chem. Edue. 1974.51,148.

Radioactiuity and Nuclear Energy sarki., V. D. J . them. ~ d u c . 1~74,51.745.

Hoffmsn, D. C.: Choppin. G. R. J. Chrm. Edur. l986.63.1059. ~ ~ h ~ ~ ~ ~ m , M . D.: Deleher. M.: Emst, A,; Hofsass, H.: Lindner, G.; Rechknagel, E.

Teaching Enuironmental Science Environment 1986,25 (5),6. Haake, P.; Dueloa, J. J Chem. Educ. 1975.52.175.

Landis. J. W. J . Chrm. Edur. 1973.50.658. Kmmel, H. 8.; Tomkins, R. P. T.: Perez, M. J . Chrm. Educ. 1980.57.798. Lester, R. K. Sci. Am. 1986,254 13). 31. Ka1b.K. E.:Tsylor.M.A. J . Chsm.Edue. 1980,57,ZO

Upton, A. C. Sei. Am. 1982,246 (2). 41. Parry. R. W . J . Chem. Educ. 1980.57.19.

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