In the Classroom edited by
JCE DigiDemos: Tested Demonstrations
Ed Vitz Kutztown University Kutztown, PA 19530
Old Nassau Demonstration with Wilkinson Modification submitted by:
Lawrence E. Wilkinson ExxonMobil Refining & Supply Company, P. O. Box 551, Baton Rouge, LA 70821-0551;
[email protected] checked by:
David Speckhard Department of Chemistry, Loras College, Dubuque, IA 52001 James H. Maynard Department of Chemistry, University of Wisconsin–Madison, Madison, WI 53711
The Old Nassau demonstration, also known as the Halloween Reaction, is a clock-type reaction that turns orange, then black in succession. A number of variations of this demonstration have appeared in this Journal and elsewhere over the years, but to my knowledge, all employ a dilute solution of mercury(II) chloride (1–12). Owing to the toxicity and environmental concerns associated with the disposal of mixtures containing mercury compounds, several years ago I began substituting a solution of silver nitrate for the mercury(II) chloride solution. Reagents Solution A: 17.0 g sodium bisulfite dissolved in 500 mL of 1% soluble starch solution. Solution B: Aqueous solution containing 15.0 g of potassium iodate per liter. Solution C: A 0.025 M aqueous solution of silver nitrate.
Procedure Place 300 mL of water (distilled or tap water; use of chlorinated water does not interfere) in a 600–1000-mL beaker. Add 50.0 mL of Solution A and stir well to mix thoroughly. I use a magnetic stirrer to provide vigorous mixing throughout this demonstration. While continuing to stir vigorously, simultaneously add 85.0 mL of Solution B and 100.0 mL of Solution C to the beaker. The mixture will turn milky white immediately as the result of the formation of silver iodate. The milky white color changes slowly to cloudy, orange–yellow as AgI forms. Some time thereafter, the sudden change to black (actually very dark blue) occurs as expected. Although not part of the original demonstration, I often finish by slowly adding sodium thiosulfate solution to the mixture. Done slowly enough, it can
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be shown that the color of the starch–iodine complex really is dark blue; it will then also be obvious that the yellow color did not change to black, but was masked by the dark color of the starch–iodine complex. Disposal The small quantity of silver iodide produced may be allowed to settle out, and retained for later reclamation of the silver (13). The solid silver iodide not thus reclaimed, and the supernatant solution, should be disposed of in accordance with local regulations. Literature Cited 1. Tested Demonstrations in Chemistry, 6th ed.; Alyea, H. N., Dutton, F. B., Eds.; Journal of Chemical Education: Easton, PA, 1965; p 19. 2. Alyea, H. N. J. Chem. Educ. 1955, 32, 9. 3. Alyea, H. N. J. Chem. Educ. 1977, 54, 166–167. 4. Lambert, J. L.; Fina, G. T. J. Chem. Educ. 1984, 61, 1037– 1038. 5. Kemp, M. K.; Hoyce, J. Chemtech 1979, 9, 210–215. 6. Anonymous. Chem 13 News 1976, November, 5. 7. Chen, P. S. Entertaining and Educational Chemical Demonstrations; Chemical Elements: Camaville, CA, 1974; pp 27–28. 8. Humphreys, D. Demonstrating Chemistry; Chemistry Department, McMaster Univ.: Hamilton, ON, Canada, 1983; No. 105. 9. Summerlin, L.; Ealy, J. L. Chemical Demonstrations; American Chemical Society: Washington, DC, 1985; Vol. 1, p 77. 10. Moss, A. J. Chem. Educ. 1978, 55, 244–245. 11. Shakhashiri, B. Chemical Demonstrations; University of Wisconsin Press: Madison, WI, 1992; Vol. 4, pp 29–36. 12. Fortman, J. J. J. Chem. Educ. 1992, 69, 236–237. 13. Bush, K. J.; Diehl, H. J. Chem. Educ. 1979, 56, 54.
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