I present this demonstration to reinforce the concepts that I've introduced about energy effects in phase changes. It could be presented as a mystery for solution by individuals, smell groups, or the class. Acknowledgment The chemistry student who made the suggestion to add acetone to water was Rick Rudherg, class. of 1990, Evergreen High School. Also, the idea to use black plastic to make the ice more visible on the video screen came from my principal, Nancy Bush-Lange, who happened to visit during my first presentation of this experiment. Literature Cited 1.HeMn. P G. Concoptun1Physlra. 5th Ed.;Little. Bmwn & Ca.. 1985,p 253. 2. Summerlin, L R.;Borgtord, C. L.;Ealy. J. L.Ckmirn1Dpmonstmtione:ASourcebod for?hockrs, Vol 2. American Chemical Satiety, 1985, p 24.
The Howling Gummy Bear Dan M. Sullivan University of Nebraska Omaha, NE 68182
The concept of energy content of foods is one of the most difficult topics to explain to biochemistry students. Certainly, they realize that eating foods high in lipid or carbohydrate content contributes to expanded waistlines, but it's difficult to illustrate the fact that we really consume hieh-enerm foods in order to obtain the reduced carbon t G y cont&. I illustrate the caloric content of foods in two wavs. After we have studied glycolysis and the Krebs cycle, fignite a Snanish peanut on a stand made of a bent Daoer clip. The clip may be bent so that the large en2 firms atrianeular base and the small end forms a rouehlv circular rine &st smaller than the peanut. The peanut&;ally burns f; several minutes. releasing a ereat deal of heat. (The caloric content of is rel&;ily high, about 6.4 kcaVg (27 J / ~orI841 kcal per cue of Seanish-stvle peanuts, (11.The eRergy content i f slightly mire than four cups of peanuts is equivalent to that of one pound of body fat. After witnessing a drama&c demonstr&ion of the oxidation of wood splints by molten potassium chlorate at the 10th BCCE (21, I devised a similar experiment using candy gummy bears as the source of reduced carbon. I promise to reward the class for future work by making a gummy bear "howl" for them. At the appropriate time, I pass out samples of gummy hear candy. We identify and discuss the ingredients listed on the wrapper and again emphasize the fact that the reduced carbon is the source of energy. In a well-ventilated area behind a safety shield and over a fue-resistant surface, I set up a ring stand equipped with a heat-resistant test tube holder. A large (25- x 200-mm) Pyrex test tube containing approximately 15 g of KC103 is placed in the holder and heated until the KC103 melts. I ~ I U Da eummv bear into the molten KC10. and stand bv with a Ere ex&guisher for dramatic effect: The candy nites and burns furiouslv with a hieh-oitched roar. ~ m v o k ing exclamations of amazement from h e class andgasps of excitement from passersby. Caloric content of gummy bear-type candy differs with suppliers, hut a n average value is probably 95 kcdoz or 3.4 kcdg.' I have found that peanuts bum more slowly than gummy bears in molten potassium chlorate, but peanuts bum more rapidly than gummy bears in air. Gummy
ig-
'Candy companies are relunant to pub icize the calor~ccontent of prod~cts.b ~ I rwi I supply sources of intormat~onupon reqLes1: most suppliers reported va Les Detween I00 kcal oz and 89.6 kcal oz. 326
Journal of Chemical Education
bears are difficult to ignite but burn vigorously once ignited; I suspect that the gummy bears are melted by the high temperature of the potassium chlorate and, therefore, present the possibility of a reaction occurring in a liquid phase rather than the liquid-solid phase observed for the buming peanut. Safety I've never had a fire or exolosion connected with this demonstration, but a fire e k i n g u i s h e r must h e available a n d t h e demonstration should h e conducted over a fire-resistant surface (small pieces of molten KC103 sometimes fly over the edge of the tube) and t h e demonstration must h e performed behind a safety shield (preferably within a hood) a n d i n a well-ventilated area. This demonstration produces quantities of smoke that I find innocuous but which might be irritating to those with sensitive lungs. The reaction can be videotaped for display in areas not equipped for demonstrations, but it is much more dramatic if seen in person. Do n o t a t t e m p t t h i s r e a c t i o n w i t h g r a n u l a t e d sugar; t h e high surface a r e a of t h e sugar particles might result in an explosion. A mixture of granulated sugar and potassium chlorate in a small cylindrical tube was once used for the purpose of splitting logs. Materials 25- x 200-mm heat-resistant test tube 15 g reagent grade KC10,
One gummy bear Safety shield and fire-resistantsurface Fire extinguisher Literature Cited I Chn.t#an..l .C.rryrr..l N u a . h n f o r l . r <
