edited by MIRIAM C.NAGEL Avo" High School Avon. CT 06001
Miriam C. Nagel Avon High School Avan. CT 06001
"Start the Term with a Bang" is the enticing title in a recent "Tested Demonstrations"(1) outlining an innovative sodium-water reaction. "4 Hurt as Beaker Explodes a t School" was a 1983 headline in theNew York Times (2). The explosion occurred soon after the teacher had mixed sodium and water together. The unpredictable nature of the reaction between sodium and water is well documented. The explosion descrihed in the New York Times was not unique (3). What is the educational value of this demonstration? There is no doubt that students will be impressed with such an introduction to chemistry. But, what are they really learning? Was it the memory of an "exciting" demo that caused a Shelton, Connecticut, youth to take chemicals from his chemistry class and store them in his locker? He had secret plans to make a Fourth of July display. Unfortunately, the heat of the June '84 day was enough to set off a premature explosion in his locker that sent five injured students and two injured teachers to the hospital (4). One student needed surgery for a fractured leg and also had head and hand iniuries. Some d&onstrations obviously court disaster. The "Combustion of Peroxyacetone" (5) involves the preparation of an extremely dangerous organic peroxide that is thermally unstable and can be highly shock sensitive. A very serious accident was reported by William Hutton of Iowa State Universitv in the Seotemher 17,1984. issue of Chemical & ~ n ~ i n e e r i News & (6).The peroxyacetone demonstration had apparently been performed without mishap for years at Iowa State prior to the fateful day. Two or three grams of unneeded solid peroxide were left in an open jar under a hood after a demonstration. As had apparently been routine practice, any surplus chemical was kept only a few davs before i t was disuosed of hv imition. For some reason. as "the jar containing the waste was being tapped to remove the unwanted ueroxvacetone for disoosal. . . a violent exulosion occurred. Pulverized glass caused severe eye and hand iniuries. In response to Hutton's letter in CKzENews, Reidar Halle, Vice PresidentTechnical. Witco Chemical Coro.. U S . Peroxygen Division, wrote '(7)that peroxyacetone can be compared to MEK peroxide which is only available as 50%, by weight, solution, or less, because it is so shock sensitive. He further states these extremely dangerous organic peroxides are even more hazardous when impurities such as dust particles settle on them. He adds that drying out further increases the risk. Halle also cites another experiment, sometimes done in schools, as extremely dangerous, the production of "tert-hutylhydroperoxide where it is purified by distillation". As an expert on organic peroxides, he expresses alarm that some chemists "suddenly discover" such facts as the explosive risk involved in the use of these organic peroxides. There are warnings included with the Procedure in the
directions for the demonstration (8) "Combustion of Peroxyacetone" as outlined in "Chemical Demonstrations A Handbook for Teachers of Chemistry". The compound is descrihed as shock sensitive. There is also a warning to "use all the solid prepared; do not store it." In the Discussion the shock sensitivity is referred to again. Information is referenced from an earlier nublication on chemical demonstrations where i t was reported that the compound was not shock sensitive hut Shakhashiri states "our exoerience clearly demonstrates such sensitivity when a sample is struck with a hammer." Now that could be a dangerous demo. Why do chemistry teachers have a penchant for explosions? In the 1960 edition of "Tested Demonstrations in Chemistry" (9)there are 26 referenced pages in the index for "Exolosions". That is more than are listed for anv other singie item in the four pages of the index. In a more recently published source, "The Alchemist's Cookbook 80 Demonstrations" (lo), 16 out of 80 demonstrations are described in the introduction by the author as "more complicated, may involve explosive or toxic materials." Just to get a perspective on what the author considers a lower risk experiment than those 16. "Smoke Screens" on Dace 11 is rated as intermediate risk. Zinc dust, powdered ammonium nitrate, powdered iodine. and aluminum oowder are listed as materials for the d e m o h a t i o n . The NFPA Guide 491M. "Manual of Hazardous Chemicals", states (Il), "A mixture of aluminum powder and ammonium nitrate can be used as an exolosive." "Aluminum powder and iodine in close contact wiil ignite spontaneously" (12). Under "zinc plus ammonium nitrate" the NFPA Guide states if "the two substances are mixed intimately and wetted with 3 or 4 drops of water, after a short time, aviolent reaction occurs" (13). "Tickling With A Feather" is the title of an article on a "useful lecture demonstration" describing the preparation and detonation of silver acetylide (14). The author admits he never succeeded in setting off the explosion with a feather. "When it is hit with a hammer, however, i t makes a satisfying hang." He goes on to suggest passing the hammer and samples around for "audience participation." There could be ~rohlems."Once I handed the hammer and beaker of samples to a student and the entire collection of samples exoloded when he reached out to take it." The author speculates that a spark from synthetic fibers in the student's clothes set i t off. Even if an instructor might personally enjoy drama and living dangerously, for whatever reason, if there is an accident and someone else is injured, the instructor could face a lawsuit and he charged with negligence. The teacher has a leeal resuonsihilitv to "act toward others as a reasonable " person should act under the same or similar circumstances" (15). The "reasonable person" in the lab is a reasonable lab instructor who could be expected to he informed of the risk potential of a demonstration. Besides the agony of an injury, is the demo worth a lawsuit? This Journal has a carefully worded disclaimer under the Table of Contents of every issue. The disclaimer in this Journal states the experiments descrihed "are directed at qualified teachers." The definition of qualified teacher is nehulous. Can it he assumed if the &
Volume 63
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Number 1 January 1986
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demo awry the teacher was not If someone is injured, was the instructor acting as a "reasonable person''?
A qualified and reasonable teacher will thoroughly search the literature for safety information before considering any demonstration, and then determine whether the b e n e f i t j u s tifies the risk. One of the hest sources for information on high risk experimentsis
