Chemistry for Everyone edited by
Tested Demonstrations
Ed Vitz Kutztown University Kutztown, PA 19530
Disappearing–Reappearing Rabbit Trick: A New Twist to an Old Liquid Nitrogen Demonstration submitted by:
Elaine K. Haub Chemistry Department, Indiana University Southeast, New Albany, IN 47150;
[email protected] checked by:
D. Michael Barnes Stevenson High School, 39701 Dodge Park Rd., Sterling Heights, MI 48313
Demonstrations using liquid nitrogen1 are a staple of chemistry demonstrators everywhere. Typical tricks used in chemistry outreach programs and classroom demonstrations include the shrinking and expansion of balloons, freezing and subsequent smashing of items such as flowers and rubber tubing, and the instant making of ice cream (1–4 ). The typical procedure for the balloon demonstration involves either slowly submerging a long, inflated balloon into a container of liquid nitrogen or pouring liquid nitrogen over an inflated balloon. When cooled to the temperature of liquid nitrogen, the balloon appears to have lost all its gas. As the balloon warms up after being removed from the liquid nitrogen, it seems to fill with gas again. When I have conducted this demonstration in front of children, they have many times exclaimed that it must be a magic trick. The children’s comments gave me the idea for a twist on the old balloon trick. I purchased a plastic magic hat and a balloon animal kit.2,3 I practiced making a balloon rabbit and found a suitable container for holding liquid nitrogen that would fit inside the magic hat.4 Using tongs to hold the rabbit’s tail, I slowly submerge the rabbit into the liquid nitrogen. This results in the disappearing rabbit. When the “deflated” rabbit is pulled from the hat, it warms up, the gas expands, and the rabbit reappears. The rabbit balloon rarely breaks upon warming to room temperature.5 Abracadabra does not seem appropriate for this trick; therefore I use instead different phrases consisting of Latin elemental names or a particularly long coordination complex name. This liquid nitrogen demonstration has been well received by audiences at both the elementary and college levels and would be appropriate for outreach programs. It is a unique way of leading into the discussion of the changes in volume of a gas with changing temperature and the kinetic molecular theory.
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Hazards Because of safety considerations, liquid nitrogen demonstrations should be conducted at a suitable distance from the audience. Notes 1. Liquid nitrogen is available at welding supply companies. It should be handled with care and kept out of contact with skin. 2. I use the Marshall Brodien Spectacular Magic Hat Kit purchased from a toy store. 3. I have two balloon animal instruction books. The one I use the most is the Qualatex Balloon Magic Kit with instruction book. The instruction manual is by Marvin Hardy (ISBN 09616600-5-8). 4. The size of the Dewar flask will depend on the dimensions of the magic hat used. An alternative to a using a Dewar is to use the bottom half of the molded Styrofoam containers that surround bottles shipped from chemical suppliers. 5. I have found the Qualatex brand balloons to be very durable.
Literature Cited 1. Nolan, W. T.; Gish, T. J. J. Chem. Educ. 1996, 73, 651– 653. 2. Harris, H. J. Chem. Educ. 1999, 76, 196–198. 3. Waldman, A. S.; Schechinger, L.; Nowick, J. S. J. Chem. Educ. 1996, 73, 762–764. 4. Summerlin, L. R.; Borgford, C. L.; Ealy, J. B. Chemical Demonstrations: A Sourcebook for Teachers, 2nd ed., Vol. 2; American Chemical Society: Washington, DC, 1988.
Journal of Chemical Education • Vol. 78 No. 1 January 2001 • JChemEd.chem.wisc.edu
