Chemical Education Today
About “Imploding Soda Cans: From Demonstration to Guided-Inquiry Laboratory Activity” Eichler's recent article (1) on converting the classical demonstration of imploding a water vapor-filled, 12 oz aluminum soda can into a guided-inquiry lab leads me to mention a modification we have used over the past decade. We were introduced to the can crush experiment by Lee Hanson (2), although we were disappointed by its qualitative nature. Our modification involves heating on a hot hot plate not only the usual can containing a small amount of water but also a weighed, dry can. While the gas temperature in the wet can rises to that of boiling water, the air in the dry can gets hotter (averaging 130-200 °C in our students' experiments). Upon cooling this hot, dry can mouth down in a room-temperature water bath, the can does not crush but partially fills with water as the air inside cools and contracts. Using a large rubber stopper to close the opening, the can and water contents can be recovered intact. The experiment requires three weighings: the original dry, empty can; the cooled can partially filled with water; and the same can completely filled with water. While the students get a bang out of cooling the can filled with steam, using these three weights, the temperature of the cooling bath water, and the gas laws, they can determine the average temperature of the air inside the dry can when it was still hot on the hot plate. Ignoring the partial pressure of water, using Charles' Law, V1/T1 = V2/T2, and a water density of 1.00 g/cm3 students are able to calculate a reasonable average temperature of the hot air in the heated can, provided that they understand what they are doing, make the correct subtractions, and use units of Kelvin. Students can be responsible for providing the specifics for the calculations. This modified can crush experiment engages our students with an interesting story as told by the molecules, which can be completed in one hour or less. In our general chemistry laboratory, it is used as an extra credit experiment worth about one-fifth
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of a regular experiment. While we do not use this experiment as a guided-inquiry lab, further aspects of the crushing can be investigated. Implosion occurs because water enters the steamfilled can more slowly that the internal pressure decreases, making this also an experiment in kinetics. This was pointed out by Vitz (3) in a similar crushing of an ammonia-filled can. Enlarging the can's opening increases the rate at which water enters the can and can be used to stop the crushing. Where crushing does not occur, over 90% of the uncrushed can fills with water. Although the crushed cans are often considerably distorted, the implosion usually produces a rather symmetrical crushing with four or five equally spaced (more or less) creases. A narrower 8 oz NesCafe can produces three creases. We use this as an identification of an implosion as opposed to other ways to crush cans. Our Web site has further information (4, 5) and a video (6) showing much of the above. Literature Cited 1. Eichler, J. F. J. Chem. Educ. 2009, 86, 472–474. 2. Hansen, L. D.; Garner, J. L.; Wilson, B. J.; Cluff, C. L.; Nordmeyer, F. R. J. Chem. Educ. 1996, 73, 840–842. Hansen, L. D.; Nordmeyer, F. R. Exploratory Chemistry Experiments I; Kendall Hunt Publishing Co.: Dubuque, IA, 1994; pp 15-16. 3. Vitz, E. J. Chem. Educ. 1999, 76, 932–933. 4. PlayChem Home Page at the Department of Chemistry, Rutgers University. http://genchem.rutgers.edu/PlayChem (accessed Feb 2010). 5. Web Site for Cancrush, a Playchem Experiment. http://genchem. rutgers.edu/CanCrush.html (accessed Feb 2010). 6. Downloadable video demonstrating the can crush experiment. http://genchem.rutgers.edu/CanCrush.wmv (accessed Feb 2010). Rudolph W. Kluiber Department of Chemistry, Rutgers University, Newark, New Jersey 07102
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r 2010 American Chemical Society and Division of Chemical Eduation, Inc. pubs.acs.org/jchemeduc Vol. 87 No. 4 April 2010 10.1021/ed8001489 Published on Web 03/09/2010
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