In the Classroom Tested Demonstrations
Ammonia Can Crush submitted by:
Ed Vitz Department of Chemistry, Kutztown University, Kutztown, PA 19530;
[email protected] checked by:
Daniel T. Haworth Department of Chemistry, Marquette University, Milwaukee, WI 53201
In a familiar demonstration that appeared for the first time in the American Journal of Physics (1), water is boiled in a 12 oz aluminum soft drink can until the can contains only water vapor at atmospheric pressure and 100 °C. The can is inverted and dipped into a shallow pan of water, which cools and condenses the vapor to water at room temperature—at which, owing to hydrogen bonding, the vapor pressure is only about 2 cm Hg. Because the inertia of the water is much greater than that of the light aluminum can, atmospheric pressure crushes the can before water has time to rush in (2). Ammonia can crush cans too—and “chemical” can crushing may be even more surprising than the original “physical” version. If an inverted aluminum soft drink can is filled with ammonia gas by downward displacement of air and then dipped into one inch of water in a shallow pan, the can is dramatically crushed by atmospheric pressure as the ammonia rapidly dissolves in the water. It may be necessary to shake the can slightly to initiate the rapid dissolution. Although the can may be filled with ammonia from a lecture bottle as part of the demonstration, it is safer to fill the can in a hood before lecture, either with a lecture bottle or with ammonia generated by standard procedures (3, 4). Ten grams of NH 4Cl and 10 g of Ca(OH)2 are added to a side-arm flask. The flask is stoppered and heated to deliver NH3 through a rubber hose to fill the inverted can, which may then be sealed with Parafilm or an oil-based clay. Ammonia gas exsolved by heating concentrated aqueous ammonia solution did not work well in this demonstration. The prepared can is then brought to the lecture hall so that risk of exposure to high concentrations of ammonia is reduced. The danger of inhaling ammonia can be inferred from the results of this demonstration.
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The same demonstration works with gaseous HCl generated by the reaction of sulfuric acid and sodium chloride (5) and added to the can by upward displacement of air. The soft drink can must be dry before either gas is added. This demonstration promotes discussion of the strength of hydrogen bonds; of solubility of polar molecules in water; of why ammonia is a gas while water is a liquid at room temperature; why ammonia dissolves so rapidly and to such a great extent in water; why a can filled with carbon dioxide or methane would not work; and why a nonpolar liquid would not work in place of the water in this demonstration. It was inspired, in part, by the many useful “fountain” demonstrations described in this Journal (6–10) and elsewhere (11, 12). Literature Cited 1. Visscher, P. Am. J. Phys. 1979, 47, 1015. 2. Shakhashiri, B. Z. Chemical Demonstrations: A Handbook for Teachers of Chemistry, Vol. 2; University of Wisconsin Press: Madison, 1985; p 6. 3. Shakhashiri, B. Z. Op. cit.; p 202. 4. Tested Demonstrations in Chemistry, Vol. 1; Gilbert, G.; Alyea, H. N.; Dutton, F. B.; Dreisbach, D., Eds.; Journal of Chemical Education and Division of Chemical Education, Inc., American Chemical Society: Granville, OH, 1994; p F-13. 5. Shakhashiri, B. Z. Op. cit.; p 198. 6. Li, J.; Peng, A.-Z.; Burgett, P. C. J. Chem. Educ. 1995, 72, 828. 7. Steadman, N. J. Chem. Educ. 1992, 6, 764. 8. Epp, D. J. Chem. Educ. 1991, 68, A297. 9. Kauffman, G. B. J. Chem. Educ. 1982, 59, 80. 10. Alexander, M. D. J. Chem. Educ. 1999, 76, 210. 11. Shakhashiri, B. Z. Op. cit.; p 205. 12. Gilbert, G.; Alyea, H. N.; Dutton, F. B.; Dreisbach, D. Op. cit.; p F-12.
Journal of Chemical Education • Vol. 76 No. 7 July 1999 • JChemEd.chem.wisc.edu
