Chemistry in Action Another Approach to Descriptive Chemistry Earl F. Pearson, Curtis C. Wilkins, and Norman W. Hunter Western Kentucky University, Bowling Green, KY 42101 Presentation of descriptive material in appropriate format is a continuine orohlem confrontine " teachine of freshman chemistry ( I ) . Some texts attempt to integrate descriptive material throughout the text with examples and prohlem assignments from practical applications (2, 3). Other texts have collected descriptive material into separate descriptive chapters ( 4 4 ) or interchapters (7). However, most professors find it difficult to incorporate such material into iectures or reading assignments hecause the packaging is not u.. ~pr. o ~ r i a tThe e . material is often too dispersed or so much is presented that it is unclear just what constitutes the important information students are expected to learn. Students and faculty alike are unable to identifythe most significant features of the information that is presented due to the wav i t is nackaeed. ;\n effort waimade to address these problems in the freshman course for chemistry and other science majors a t Western Kentucky University. The course design has been described elsewhere by Hunter (8).This fall a series of papers on descriptive topics was included in the course materials. An effort was made to collect information for the papers from a number of sources and to condense i t to a package suitable for incorporation into the lecture. The length of each paper is kept to no more than one typed page. The papers are not intended to he a n exhaustive treatise on the subiect nor do thev alwavs contain the latest research in the area. An attempt is made to present some of the most signifit cant descrintive features of the suhiect. i m ~ o r t a nindustrial reactions, and to stress, where appropriate, the impact of the subject on the profession or society. Lecture presentation of these papers usually takes the form of presenting an overhead transparency of the paper for students to read while the important features are discussed for emphasis. Discussion usually takes 5 to 10 minutes of class time for each subject presented. Copies of each of the papers are kept in the Chemistry Learning Laboratory, a study/help room staffed by faculty and graduate students (and occasionally hy an outstanding undergraduate student), and in the science library in a reserve file called "Chemistry in Action". Students are instructed to make copies of the papers for n e each hour exam. more careful studv while ~ r e ~ a r i for Four hour e x a d s are gfved in the course, and usually two "Chemistry in Action" topics are chosen that best match the material covered by each hour exam. However, a close connection is not always possible nor even desirable. Some of the topics answer questions concerning materials or processes that are of current public interest hut are not covered in other course materials. Four representative "Chemistry in Action" papers are presented here. Titles in the series include:
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1. Ozone 2. Sodium Chloride 3. The Akali Metals 4. FIuorine, A Halogen 5. Ethylene 6. Synthetic Polymers I . Sulfur/SulfuricAcid 8. Phosphorus 9. Water
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10. Two Commercial Voltaic Cells 11. Chromium: A Transition Metal
12. Iran: Another Transition Metal 13. Nitrogen, Ammonia, Nitric Acid 14. Nuclear Power, Fuel for Thought 15. Biological Effects of Radiation 16. Chernobyl-Three Mile Island-What Really Happened 17. Chernobyl-Three Mile Island-A Contrast Worth Noting Those wishingto have copies of the "Chemist~yin Action" series in the one-typed-page format should request them from the authors. These copies may he used to prepare overhead transparencies or reserve copies for libraries. There is no charge for the copies. 1. Bent, H. A. J. Chem. Edur. 1984.61.985. 2. Zumdahl. S. S. C h e m i s f v ;Health: Lexington, MA, 1986. 3. Ebbing. D. D. Oenaral Chamistry, 2nd ed.; Houghtan-Miflin:Baston. 1987. 4. Petmci,R. H. Genwol Ch~miarryluirhQuolilotiueAnolysis,2nded.:MscmiUan:Near Yo& 1987;Chspten 13, 21-23.27. 5. Brady, J. E.: Humiston, G. E. Gznarol Chemistly-Plinriplw o d Structure, 4th ed.:
Wiley: New York. 1986: Chapten 19.20. 6. K0tz.J. C.; PurcelLK. E. Chamisfry&Chemi~olReacriuity;Ssmdddd:NewYork,1981; Chapten 2 M S . 7. McBuanie, D. A,; Rock, P. A. General Chemistry, 2nd ed.;Freeman: New York, 1987. 8. Hunfer.N. W . J .Col. Sci. Teach. 1980,10(1),39.
Ethylene Physical Characterlstlcs Ethylene (ethene)is a colorless gas with a sweet odor and taste. It boilsat -103.71 'C,freezes at -169.15 'C, and has a density at STP of 1.363 gL. Its critical temperature is 9.6 'C, and its critical pressure is 50.55 atm. It is a planar molecule: H\ /c = c,/ HH TheC-H bonddistance is 1.071A.The C=C bonddistance is 1.353
A and the HCH bond angle is 119'55'.
Occurrence Ethylene is a trace component (less than 1%)of crude oil and natural gas and is given off during the ripening of fruit. It is made commercially as a byproduet of the steam cracking and reforming stages of petroleum refining. While approximately97%of petroleum is burned for fuel, the remaining 3%supplies sufficient feedstock for the chemical industry. Annual ethylene production capacity in the United States is estimated at 38 billion pounds. With actual praduction in 1984 to 24.1 billion pounds, it ranks fifth in production, Ethylene can be prepared in the laboratory by dehydration of ethyl alcohol using hot concentrated sulfuric acid. Comrnerclal Usage Ethylene is used in combination with other gases in anesthesia, as a ripening agent for fruit, and in the manufacturing ofpolyethylene. If ethylene is added to meen fruit during-shioment. . the fruit will be ripe an arrival with lessbruising and spoilage. Ethylene is used as the starting material from which many industrially important chemicals are made. It is hydrated to form ethyl alcohol (1.1 billion pounds). It is oxidized to ethylene oxide (5.6 billion poundsl for hydration to ethylene glycol (4.6 billion pounds1 for use as antifreeze. It is chlorinated to form ethylene dichloride (1,l-dichloroethane)(11.6billion pounds) from which vinyl chloride
(6.9 billion pounds) is made. Vinyl chloride is used to make PVC plastic (6.3 billion pounds) for use in automobiles, as synthetic leather, plastic pipe, and other important items. Ethylene is also reacted with benzene to produce ethyl henzene (8.9 billion pounds). Ethyl henzene is dehydrated t o make styrene (7.7 billion pounds) from whieh polystyrene is made. Polystyrene is used to make insulating containers (Styrofoam) and in making synthetic rubber (1). Polyethylene (13.98 billion pounds) is the most important industrial plastic and used to make a variety of products such as bottles, plastic wrap, pipe, cover for wires, plastic cabinets, and toys. The physical properties of polyethylene can be adjusted t o meet specific application requirements by regulating the reaction conditions and the concentration of polymerization initiator (such as benzoyl peroxide-acne medicine!). A rigid, dense plastic results if relatively few polymer chains grow and almostno branching occurs (low initiator concentration and mild reaction conditions). A softer, more pliable, and less dense plastic results if the polymer chains are highly branched (higher initiator concentration and severe reaction conditions). Ethylene is used in the production of monomers for making many other plastics. Indeed, almost all the plastics in use today may he thought of as being formed from a derivative of ethylene in which one t o all four hydrogen atoms have been replaced with another atom or group. Thus, ethylene is the "foundation chemical" for the plastics industry and accounts for six of the top 50 chemicals in production in 1984.
Literature Cited I. ~ d ~ d t i estimates o n taken from Chemicol ondEnginaaring News, May 7,1984, whieh utilized the following sources: Bureau af the Census, Bureau of Miner, International Trade Commission. C&EN estimates.
Ozone in the Stratosphere Thelevel of ozone worldwide is decreasing by about 0.5% per year in the stratosphere (the region of the atmosphere from about 12 to 50 km above the surface). The ozone level over Antarctica, however, is decreasing much faster (about 2.5% per year). During October 1985 the Antarctica ozone levels dropped about 50%-a decrease of unprecedented proportions (I). (The ozone level in the Antartica later returned t o near normal-but this enormous fluctuation in ozone concentration attracted extraordinary attention from scientists.) Ultraviolet radiation can dissociate ozone:
I t is this reaction that is responsible for ozone's absorption of ultraviolet radiation that would otherwise reach the Earth's surface. (Sienificant ozone dedetion would result in significant global . warming.) The ozone layer is threatened by chlorofluorocarbons (CFC's). The most eammonly used CFC is Freon-12, CCI2F2.The chemical inertness of CFC's makes them valuable but also creates a problem, since they remain a long time in the environment. Reactions that may deplete ozone are typified by the following (2,3):
reacts with more oxygen to farm nitrogen dioxide ( N o d . Then ultraviolet rays from the sun trigger the reactions that produce ozone:
The concentration of ozone is approximately 0.010 ppm in the troposphere and is approximately 0.012 ppm in the stratosphere.
Ozone industrial Uses (2) Ozone is more effective than chlorine in the treatment of water. I t has a stronger oxidizing capability, and it kills bacteria and viruses much faster than does chlorine. However, ozone must he generated at the place where it is used. Chlorine is therefore more convenient t o use. Tons of ozone are used each day to sever organic double bonds (primarily for the purpose of converting oleic acid t o pelarganic acid). Pelargonic acid is an intermediate used in the manufacture of plasticizers and synthetic lubricants. Ozone is used to break the double bond in raw materials that are used to produce steroid hormones, including cortisone and the male and female sex hormones. Literature Cited 1. Emhe1.L. R..et sl. Chem.Eng.Ner. I986,Nou. 26. 2. Cook,G.A. J. Chem.Educ. 1982.59.3'32.
Water Fresh Water Fresh water that has been in contact with the earth for same time contains as major ionic constituents, Nai, Kt, Caz+, Mg2+, CI-, S042-,and HCOJ-. Hard water contains appreciable amounts of the divalent cations, primarily Ca2+,Mg2+,and Fez+.Hard water may he softened by adding washing soda (Na2COd and lime (CaO), whieh forms insoluble calcium carbonate and magnesium hydroxide and ferrous hydroxide, which, in turn, can be removed by filtration. Hard water is softened in many households by an ion-exchange method in which the water is passed througha bed of zeolite (zeolite is a complex sodium aluminum sulfate). In this process sodium ions replace calcium and magnesium ions:
In municioal water treatment svstems chlorine eas is used as an vxidiliny agent todestroy harmful hacwriar. 'l'hr hypwhlon,usacid formcd b) the chllmnr i i the effectivr strrilizine ngrnt.
A very small concentration of approximately 1ppm of hypochlorous acid is sufficient to kill bacteria. This concentration is harmless to humans.
Seawater Seawater averages 3.5% by weight of dissolved minerals (i.e., 35,000 ppm), which makes it unfit for agricultural use or for human consumotion. Some nations such as Kuwait must (because of such a short supply of fresh water) remove the salts from seawater in order to obtain water suitable for drinking and for agricultural use. Most of the ionic constituents of seawater enter the ocean in superheated (320 T ) mineral-rich water that flows through vent holes in the ocean floor Temperature, oxygen concentration, carbon dioxide concentration, phosphate concentration as HPOd2-,and nitrate concentration olav an imoortant role in the chemistrv and biochemistr~of the oceans. All of the constituents mentioned are essential as nutrients far marine plants and animals. The simplest elements of the food chain are the phytoplankton, minute plants in which COI, H20, NOa-, HPOd2-, and ather nutrients are converted by photosynthesis into plant organic matter. The concentrationof NO3-or HP042-is the limitingfactar in the rate of formation of organic matter via photosynthesis-C02 is always present in excess. All the higher forms of life in the ocean are ultimately related to the phytoplankton. In certain regions of the ocean, where seasonal upwellings of nutrient-rich lower ocean layers ~~~
Ozone in the Troposphere In the troposphere (the region of the atmosphere nearest the earth) the ozone concentration level is so high (opposite to the problem in the stratosphere) as to pose an environmental problem. Ozoneis one ofthe most powerful oxidizing agents known. It attacks almost anything-fabric, plants, lung tissue, tires, etc. I t can react with other air pollutants to form substances irritating to eyes and Iunes.
Nltnraen mmoxidr [NO) is furmed by thr direct romhination of nnrqynand ox,gt.n inside an automobile cylinder. The NO i n turn
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ucrur, t h rate ~ uf p h o f ~ s y n t h e ~may i r bccome w r y high. and in t u r n the fish population is very high. Only thrcr suhstancei arc at the prr,enr time heinr recurcred from seawater in commercially important amounts: sodium chloride, bromine, and magnesium.
Chernobyl-Three Mile Island: What Really Happened The incident a t Three Mile Island was caused by a shutdown of a secondary water supply pump due to a blockage in the line. The automatic sensors detected the failure and began corrective measures. The turbine generating electricity was turned off, auxiliary pumps were turned on to increase coolant in the core of the reactor, and the control rods were inserted in the reactor to effect a shutdown. However, during routine maintenance the valve controlling flow of water from the auxiliary pump to the core had been left closed, afact unknown to the operators. The temperature of the core began to rise and some of the water in the core was vaporized creatine..messure in the o r e of the reactar. This caused a relief valve rd open and release comp 1.1 the :3sc- in ~ r d e to r IOWCI the ~ T ~ S C U I C 'This 13 normal and should hare occurred. However, the valve failcd co close. and rhc cnolanr in rhc cure nrntinurd ro bail and cscapc through the valve. The system began to take drastic action by flooding the containment building. Shutdown would have required the loss of the reactor for severai months for cleanup and reinspection by the federal government. It was February, and the region needed the electricity. The operator thought the auxiliary pump was pumping too much water into the core. Again the operator interrupted the automatic system and took measures to remove water from the core. Because the operator misinterpreted the information supplied by the sutomatic system and tampered with its operation, about two-thirds of the reactar core was left uncovered and the temperature may have reached 2000 "C. A large amount of radioactive water was dumped onto the floor of the containment building and a small quantity of radioactive gas was released into the atmosphere.
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Although the Three Mile Island reactor may have approached meltdown, actual meltdown did not occur, and no major loss of integrity of the building or the reactor core occurred. The safety equipment performed exactly as it was designed to perform and, if the operators had not interfered, the reactor would have remained safe. Much of what occurred a t Chernohyl can only be speculation, since the U.S.S.R. will not release the details. Probably the Chernoby1 reactor lost coolant due to mechanical or human error. The temperature of the reactor core began to rise, and, since the moderator (graphite) was still present, i t was far mare difficult to control the temperature. The fuel rods began t o rupture and release highly radioactive fission fragments. The operators probably flooded the reactor with water in an effort to cool the core. However, the core was so hot that the zirconium (used to hold the fuel) catalyzed the decomposition of water to hydrogen and oxygen. This explosive mixture of gases was ignited by the hot reactor and blew the top off the reactor and the containment building. The highly radioactive material was scattered aver the surrounding area exposing all those in the immediate vicinity to certain death. When the reactor was ruptured and exposed toair, the hot graphite began to burn sending a plume of radioactive smoke and dust around the world. All attempts t o put out the fire with extinguishing materials only added to the smoke and scattered more of the fuel into the atmosphere. The fire burned for several days before it was extinguished by dumping tons of lead, sand, and dirt on the reactor through the opening in the roof of the containment building. The reactar was literally buried alive. The reactor is continuing to generate heat today. It seems unlikely that it will ever he possible to stop the reador and effectively contain it. It appears that the reactor is not melting through the earth although there is a danger that ground water could get into the reactor and set off another explosion. The area may never be safe for the citizens to return to their homes ( I ) .
Literature Cited 1. Atwood, Charles H. "Nuclear Enerpy: What Can We
stllndingolSeienco 1986.5-8.
Tell the Public",Puhlic
Under
