A Program of Science Demonstrations by College
Dan M. Sullhran University of Nebraska at Omaha. Omaha, NE 68162
I was 13 when my seventh-grade teacher' mixed dilute sulfuric acid borrowed from the high school laboratory with granulated sugar to bring about a dehydration reaction resulting in a foamy black solid that rose like a huge worm out of the beaker, hissing odors of burned sugar and oxides of sulfur. Although she was not highly trained in science, she knew how to teach. She was even able to explain what was happening in chemical terms and t o convince us that sugar really was a carbohydrate. I t was not until I had actually taught chemistry, physics, biology, and mathematics that I had enough comparative experiences to choose chemistry as a career, but that single demonstration convinced me that I wanted t o become a science teacher. Nearly every science teacher and scientist I have known traces his or her interest in science back t o one such demonstration or experiment. For many grade school students, however, and in particular for students of private schools, such demonstrations are few in number and lacking in variety. Our elementary school teachers often lack the necessary science training, and their schools simply lack the resources. At the same time, our preprofessional students need experience, public speaking opportunities, and chances to serve others. Atthe University of Nebraska in Omaha, we provide a program of demonstrations through our Science Ambassadors that addresses many of these needs. Each year Irecruit students willing toserve as demonstrators. Some come from among our chemistry majors, some from our Pre-Medical Professions Club, and some are maiors in science education. I trained the orieinal demonstrators several years ago; now, current members enjoy training other students. We send letters describin~our activities to administratorsof local school districts. They, in turn, supply us with authorization and with a list of addresses of schools or inform the schools through their communications procedures and bulletins. Individual teachers contact us through our telephone recorder and schedule a visit from one of our demonstrators. Demonstrators determine the grade level and specific subject matter to he covered and pick appropriate activities for a scheduled visit. We provide suitcase-sized demo kits alone with eeneral sueeestions and snecific safetv rules. At the present time we are inaugurating a program in cooneration with our Office of Admissions to brine elementar; school children onto campus for a visit to ouFfacilities, and we are scheduling chemistry demonstrations as part of
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this visit. We helieve that the exnosure to our c a m ~ u atmos sphere will encourage more children to study science and to attend colleec. The visits have been verv o o-~ u l a rwith children, their teachers, and families. Demonstrations vary with grade level and with the interests of teachers, but we go in for flashy experiments with color changes and a few hooms and bangs illustrating scientific principles that can be discussed and easily understood, yet leave some questions for students to think about and discuss. Must of ihese demonstrations are in common use or are published in manuals of demonstration experiments.? Among our popular experiences are boiling water in a clean duplicator fluid can, capping the can, and allowing air pressure to crush it as the can cools. (This can also be done with a soft drink can. Simply boil the water in the can and rapidly invert the can in a pan of cold water for a dramatic implosion.) This is good for 5 t o 10 minutes of discussion and even some mathematical cluestions to be solved later bv the class. "What do you see happening? What do you think is happening? What do you think is causing the can to cave in? How does the heat get from the outside of the can to the water inside? What does the heat do to the molecules?" (We often explain that molecules are constantly dancing and that the music to which they dance is heat.) "What is left inside the can after it is crushed? How could we straighten the can out again? Is there anyone here with strong lungs?" (Have someone blow hard into the cooled duplicator fluid can.) "What is the area of the can? If air pressure is 14.7 pounds per square inch, what is the force on the can in pounds? In tons?" We believe that i t is important for students to begin early the process of distinguishing actual observations from tentative explanations.
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A Portion of this material was presented at the 10th Biennial Meating of the Divlslon of Chemical Education at Purdue University, Lafayene, IN, on August 3, 1988. ' Mary Lenz, Corning Public Schools, Corning, Iowa. Aiyea, H. N.: Dunon, F. 8. Tested Demonstrations in Chemistm Journal of Chemical Education: Easton, PA, 1965. Shakhashiri, 8. 2 . Chemical Demonsirations, A Handbook for Teachers of Chemistw University of Wisconsin: Madison, 1983. Summerlin. L. R.; Borgford. C. L.; Ealy. J. 8. Chemical Demos strations. A Sourcebook for Teachers; American Chemical Society: Washington. DC. 1987.
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The iodine clock reaction provides an introduction to chemical kinetics and shows the relationship of rate of reaction to concentration. There is always some child eager to use a new watch to time the reaction in seconds; other students may be involved asofficial ohsewers to say "start" and "stoo". "Do vou think the reaction would be faster or slower if the chemicals were more dilute? Do you want to try it?" (The answer t o that question is always "yes".) Children are very intuitive; as scientists and teachers, we are often criticized as being too objective. This particular experiment provides a chance to mix intuition and objectivity in proper proportions. "What do you think would happen to the reaction ~ - - time - ~ if we cooled or warmed the chemicals? How do you use this principle to control the rate of chemical reactions in your home?" We find that children love t o he included in the discussion and are always eager to answer questions or voice opinions, and we believe that this participation by children is essential to the success of the demonstration period. Demonstrators ask questions such as: "Who were the alchemists? What were they trying to find?" We initiate a discussion of alchemists and their modern counterparts by changing a copper penny into silver (coating it with zinc by heating a polished pre-1982 copper penny along with 6 M NaOH and powdered zinc in an evaporating dish) and then into fake gold by heating the coated penny in the flame of a burner in order to form a brass alloy.4 (The residue from this demonstration must be washed thorouehlv before i t is discarded.) This is usually followed with a disiussion of defacing coins and the story of my Uncle Charlie whocollected hundreds of buffalohead nickels, then drilled a hole in each and strung them together so he would not lose them! For a junior high class, this provides an excellent lead-in t o a discussion about entropy. (Uncle Charlie and his coins are both long gone.) Liquid nitrogen is used to freeze fruits or flowers prior to demonstrating their brittleness. We pour liquid nitrogen nver a balloon of oxveen ... eas. ., . deflatine the balloon and forming liquid oxygen. A cigarette placed inside can be cut out of the balloon and ienited to demonstrate the action of liquid oxygen as an oxi&zing agent (watch out for filter tips; they can take off like small rockets). We perform a little chemical magic by making a calcium acetate>thanolgel (on the order of "canned heat"), ienitinn it, and producing colored flames by sprinkling thechlorid& of pot&sium (mention banana skins), sodium (mention sodium vapor lights), strontium, and copper (11) (mention Fourth-of-July fireworks) into the flame. We illustrate the effects of surface area on rate of reaction while producing a dust explosion by blowing lycopodium powder into a flame. (Powdered nondairy creamer eives similar results.) In most amicultural states, afew main ilevators and flour mills explobe each year. "Why d&sn't the dust from our floors explode?" The dust on our floors is actually a much more complex mixture than we commonly think.'"What kind of dust io flammable'!" Several kinds of plastics may be produced either from storeroom materials or from components purchased commercially. We make this the basis for discus~ionsof monomers and polymers and also for discussion of environmental effects of use and disposal of materials. "We commonly recycle aluminum cans. Can plastics he recycled?" (Recycled plastic is, in fact, being used to make nlastic lumber and shionine pallets.) "What commonly discarded mater~alsare bibde&dable9" Mobt of our demonstrations end with a bane. We work up to it by referring to several balloons that havd-been hanging or Ivine around durine the demonstration. We ask "What do tl&k is in the ;ellow balloon? How would inhaling helium gas affect a person's voice? Why does it sound so high-pitched? What do you think would happen to the pitch if a person inhaled a very heavy gas?" (We use a supply of higl;-puritysulfur hexafl"oride todemonstrate the etfectsof a very dense gas. SFc exhibits some unusual properties: A ~~
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balloon of SF6 will swell over a day or so until i t explodes rather than gradually deflating as it does if filled with air or helium, and balloons of SF6 exhibit trajectories markedly different from those of balloons of air when tossed from nerson to ~erson.)Accordine to an example commonlv used by physicsteache;s, there ;a about as many molecules of air in a breath as there are lunes full of air in our atmosphere, so each breath probably contains a molecule t h a t Jesus breathed as well as one breathed by Hitler and one inhaled by Attila the Hun. (We breathe about 20,000 L of air daily, and one can calculate that we have a pulmonary surface area in the lungs, of 60 to 80 m2.) The sulfur hexafluoride and, with a little practice in taking small breaths, demonstrators find that they can hold agroup spellbound for several minutes as they talk about pollution and the effects of micron-sized particulate matter which can go down into the alveoli of the lungs carrying concentrated poisonous gases, therebv causine ereater damaee than the easeous pollution alone. w e end%; asking "what do you &ink is in the red balloon?"and then ignite a balloon full of hydrogen . . by using a burning splint attached to the end of a meter stick: (Chic dren should he warned to cover their ears.) If the lecture room has a high ceiling, the string can he ignited and the balloon will float up toward the ceiling and explode. (This is dramatic but may loosen ceilingtile.) We caution students to inhale only those things their teachers or parents consider safe, and then only in the presence of the teacher or parent. Demonstrators study a list of safety rules prior to each demo and are trained to emphasize safety and concern for the environment a t every opportunity. They, in turn, stress safety to students. "What part of your body is most easily injured by chemicals?" "We've just started a small fire. How can we extinguish it safely?" We also stress observation and experimentation. "What did you observe? What do you think caused that? How could we test that hypothesis? Would you like to try it?"Every class has one or two children who want to answer every question and one or two who don't want t o answer anv ouesiions. I t is a real challenee for a ~~-~~ college student to keep an especially entliiusiastic chyld from mnno~olizine the discussion while encouraeine-. a ouiet -. child to participate. It is not unusual to have a teacher later report that this was the first time a particulat- child had ever seemed excited by a science activity. I t is difficult to iudee the value of a program such as this, but we receive many ietters and pers&aicomments, along with many hand-written or drawn messages describing child r e n ~ positive ' reactions to the demonstrations. Some of these children later enroll in our college-level chemistry classes. Many of them will become teachers. All of them, we hope, will see the charm and fun of science and carry away n&tions that thev will soend months or vears answerine. (I &d not figure out
