--..- - - , GEORGEL. GILBERT Denisan University Granville, Ohio 43023
A Chemiluminescent Ammonia Fountain Sueulmo BY
Nlcholas C. Thomas
Auburn Unlvenlty at Montponury Montgomery. AL 36117.3596
Joseph H. Drelsbach University Id Scranton Scranton, PA 18510 Including lecture demonstrations in the teaching of chemistry not only illustrates important chemical principles but c&also arouse the interestand curiosity of &ude&s. Two popular and dramatic demonstrations offered to student audiences that virtually guarantee their undivided attention (at least for a few moments) are the ammonia fountain and chemiluminescence experiments. While both are safe, easy to set up, and instructionally significant demonstrations, they illustrate strikingly different principles. Each has its own educational value and the pedagogical aspects have been well documented (e.g., see Shakhashiri's Chemical Demonstrations: A Handbook for Teachers of Chemistry). In summary, the ammonia fountain experiment illustrates dramatically the solubility of a gas in water and consequential pressure reduction,' while the mixiug of two solutions that luminesce clearly demonstrates the conversion of chemical energy to light energy.2 We have found it possible to combine these demonstrations to give a spectacular display of chemilumiuescence utilizing the siphoning effect of the ammonia fountain. We have used the experimental set up that isshown in the fieure. An inverted 2-1. round-bottom flask containine ammonia gas is connected via a T tuhe to the two solutionsto be mixed to produce the chemiluminescence (solutions A and B). When a small quantity of water is injected into the ammonia flask, the reduction of pressure causes solutions A and B t o he simultaneouslv drawn into and mixed in the inverted flask. In a darkened room, this produces a brilliant blue luminescent fountain. A ~ h o t o-e r a.n hof the demonstration appears on the cover of this issue. Experlmenfal Materials Required 2-Lround-bottom flaskwith two-holed rubber stopper. Clamp and retort stand. Eyedropper with large ruhber hulb filled with water. Three pieces of glass tubing (two L-shaped pieces, one straight piece). T-shaped glass connecting tube. Three short ~iecesof clear nlastic tuhine. Sources ofammonia gal (if a commerc~alcylinder is unavailable the ammonia may be generated by heating a mixture uf 10.0 g of ammonium rhloride and 10.0 g of calcium hydroxrde in 10 ml. of
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Soluriona fur chemiluminescenre.' (Solution A is prepared by dissohing 4.0 g of sodium carbonate in 500 mL of distilled water, adding0.2 gofluminol,and stirring todissolve. Sodium birarbon-
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Shakhashiri, 6.2. Chemical ~emonshatlons:A Handbook for Teachers of Chemisby; University of Wisconsin: Madison, Wi. 1985; Vol. 2, p 205. Ref 1; VOI. 1. p 156. Ref 1; Vol. 2. p 202.
Solution B
Solution A
Arrangement of apparatus u6ed in the chemiluminescem ammonia fountain.
ate (24.0 g), 0.5 g of ammonium carbonate, and 0.4 g of copper(I1) sulfate are then added with stirring until all the solid dissolves. Dilute to 1L with water. Solution B is prepared by diluting 50 mL of 3%hydrogen peroxide to 1L with distilled water). Two l-L Erlenmeyer flasks (for solutions A and B). Procedure The apparatus is assembled as shown in the figure. As a precaution, the ruhber stopper in the inverted flask should he clamped or secured with a strong ruhber band. The room lights are turned out, and the rubber hulb connected to the eyedropper is squeezed to introduce several milliliters of water into the ammonia-filled flask initiating the fountain and chemiluminescence effects.
Discussion The fountain effect lasts for about 2 min producing a slow and constant mixing of the two solutions, and thus a steady, intense glow results that is clearly visible even in large lecture rooms. The solution continues to glow for another 2 min. The presence of the ammonia gas has no affect on the chemiluminesceuce since basic conditions are required for the luminol oxidation, and, even hefore mixing, solution A is quite basic (pH = 9).2The disposal procedure for solutions and experimental hazards are documented in the original references.1-3 Volume 67
Number 4
April 1990
339
