In the Classroom
Tested Demonstrations
Icarus and Sun, Not Only in Mythology but Also in the Laboratory!† submitted by:
Mrinalini G. Walawalkar and Herbert W. Roesky* Institut für Anorganische Chemie, der Universät Göttingen, Tammannstrasse 4, D-37077 Göttingen, Germany; *
[email protected] checked by:
Paul F. Krause Department of Chemistry, University of Central Arkansas, Conway, AR 72032
Stories of fire started by the sun date back to Greek mythology. An interesting tale is of an Athenian craftsman named Daedalus who had a number of apprentices in his employ. One of them, Talos, proved to be a better craftsman and a threat to Daedalus, and therefore Daedalus murdered him. To escape from the consequent sentence Daedalus, fled with his son Icarus to the island of Crete; but unfortunately they were put in prison. Daedalus used his craftsmanship and attempted an escape by making wings of feather and wax for both himself and Icarus. He warned Icarus to beware of the sun, but Icarus did not take the admonition seriously. He flew too close to the sun and perished. This story can be related to the following experiment, which is a good example of creating a combustion without using any harmful or dangerous chemicals in the classroom.
A
B
Methodology The materials required for this demonstration are potassium nitrate (KNO3), water, a piece of paper (paper napkin, ink-blotting paper, linen cloth piece, circular filter paper), a clamp, a stand, a marker pen or a pencil, and a lens to focus sunlight. Dissolve the potassium nitrate in water to prepare a concentrated KNO3 solution. Select a piece of paper and dip it into the saturated KNO3 solution. Allow it to get thoroughly soaked; then drain it and allow it to dry overnight at room temperature away from any combustible materials. Fold this dried KNO3-coated paper into a small paper plane. Write the name “Icarus” on one side of the plane using a marker pen. Also randomly place a couple of black dots on the paper. Suspend the plane using a thin copper or aluminum wire on a clamp (Fig. 1). Bring this assembly to the sunlight. Let the sun shine on the whole assembly for a few minutes; nothing happens! Then use a focusing lens and try to focus on a point on the paper where nothing has been written. Still no change!! Then focus the sunlight on a point where “Icarus” is written or a black dot appears on the paper. Combustion is initiated in a very few seconds.1 If you try to carry out the reaction without the presence of Icarus or black dots on the plane, nothing transpires. The plane remains unchanged. A control is prepared in the same manner as the plane above except that it is made of a piece of paper that has not †
This paper is dedicated to Professor Richard P. Kreher in great appreciation.
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Figure 1. A: The experimental setup showing light being focused on a black spot on the KNO3-soaked paper plane. B: Combustion is initiated. C: The paper plane burns extensively.
Journal of Chemical Education • Vol. 78 No. 7 July 2001 • JChemEd.chem.wisc.edu
In the Classroom
been treated with potassium nitrate. Exposing it to sunlight produces no evidence of burning on the white area and only marginal, confined burning, on the black spots. For total burning of the paper, potassium nitrate and a blackbody are essential. Normally, to generate fire using chemicals (1–3) one requires white phosphorus in CS2 (harmful substances to handle in a normal classroom); or Na2O2, which is quite dangerous as it generates H2O2; or a H2 and O2 mixture, which is explosive; or, simply mixing sodium metal with water or potassium permanganate and glycerine. The last experiment is difficult to start, but the reaction accelerates as the system becomes hotter and catches fire. The nitration of cellulose has served as the source for some spectacular flame tests (4 ), and guncotton (1b) is used for a similar demonstration. However, more dangerous chemicals are involved in those preparations. Explanation Cellulose is the major component of paper. It is poly-βglucopyranosoid (1,4-coupled) with a molecular weight close to 500,000. As the sunlight is focused on the spot marked with ink, the spot functions as a blackbody and absorbs a large amount of energy. This energy is enough to initiate the oxidation of cellulose by potassium nitrate. A blackbody, in physics, is theoretically a perfect absorber and emitter of invisible as well as visible radiation. Any substance, such as coal or pitch, that absorbs nearly all the light falling on it and reflects very little approximates a blackbody.
Hazards Potassium nitrate is an oxidizer and any contact with flammable substances should be avoided. Any combustion is dangerous, and therefore glasses and protective gloves must be worn. A fire extinguisher should be kept at hand. Acknowledgments We are thankful to the Fonds der Chemischen Industrie for financial support and to H. Fraatz for technical help. The comments of the referee were extremely helpful. Note 1. This reaction also proceeds with a simple single black dot on the paper, but Icarus makes the experiment more interesting.
Literature Cited 1. (a) Shakhashiri, B. Z. Chemical Demonstrations: A Handbook for Teachers of Chemistry; University of Wisconsin Press: Madison, 1983; Vol 1, pp 74–75. (b) Ibid.; pp 43–45. 2. Roesky, H. W.; Möckel, K. Chemical Curiosities; VCH: Weinheim, Germany, 1996. 3. Roesky, H. W. Chemie en Miniature; Wiley-VCH: Weinheim, Germany, 1988. 4. Peyser, J. R.; Luoma, R.; George, A. J. Chem. Educ. 1988, 65, 452.
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