In the Classroom edited by
JCE DigiDemos: Extensions
Ed Vitz
Kutztown University Kutztown, PA 19530
Demonstration Extensions: Flame Tests and Electrolysis Demonstration Extension: Flame Tests Another suggestion for demonstrating flame tests has been added to the JCE DigiDemos online collection (1). Tom Mortier, Annie Wellens, and Marie-Josée Janssens use aluminum tea light candle holders to make alcohol burners for flame tests. Flame Test Safety Methanol-fueled flame tests have been the cause of several recent accidents involving large fires, probably resulting from containers of methanol being near the small sample of burning methanol. If the burning methanol gets too hot, it may vaporize and flare up. The Laboratory Safety Institute has documented serious accidents of this kind, including one where six students were seriously burned (2). In “Inexpensive Alcohol Burners for Flame Tests Using Aluminum Tea Light Candle Holders”, the authors suggest that the methanol solution be added to small aluminum cans placed in Petri dishes half filled with water. This precaution keeps the burning methanol cooler, and more importantly, may draw attention to the flame hazard. No accidents have been reported if safety shields are used and large containers of methanol are removed from the area. Many flame test demonstration methods can be found through the JCE Demonstrations Index (1). We are aware of candles which contain dissolved substances so that they burn with red, green, blue, orange, purple and white flames (3). These are expensive, but provide a safe and convenient method of demonstrating flame tests. The flames are dim, but if viewed in a dark room with a prism spectroscope the sodium lines in the “white” candle are much more prominent than in the spectrum of normal candles (which are usually continuous spectrum due to incandescent carbon). With “spectrum glasses” (4) it is possible to distinguish red and yellow “lines” (flame images) in the red candle, poorly resolved “lines” in the green candle which probably are due to boric acid (5) or barium
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mixtures, and poorly resolved “lines” in the blue candle probably due to mixtures including copper salts. Demonstration Extension: Electrolysis Another suggestion for demonstrating water electrolysis at iron nail electrodes has been added to the JCE DigiDemos Forum where the traditional experiment is described (6). In this variation by Mark T. Stauffer and Justin P. Fox, 1,10-phenanthroline chelates Fe2+ formed at the anode, and thymolphthalein indicates formation of OH‒ at the cathode. A striking orange and blue contrast is produced in the sodium sulfate-impregnated gelatin. Literature Cited 1. JCE Digital Library: DigiDemos; http://www.jce.divched.org/ JCEDLib/DigiDemos/index.html (accessed Feb 2008). 2. The Laboratory Safety Institute: News; http://www.labsafety.org/ news.htm (accessed Feb 2008). 3. Imported by GloCo Candles (http://www.glococandles.com) but sold only through distributors, including the New York Museum of Modern Art (http://www.momastore.org) (accessed Feb 2008). 4. Many science educational materials suppliers sell these, including Rainbow Symphony, http://www.rainbowsymphony.com/rainbowfireworks-glasses.html (accessed Feb 2008). 5. JCE Software: Chemistry Comes Alive! Boric Acid in a Burner Flame; http://www.jce.divched.org/jcesoft/CCA/samples/cca7boric. html (accessed Feb 2008). 6. JCE Forums—G-35 Demonstration of Electrochemical Cell Properties by a Simple, Colorful Oxidation–Reduction Experiment. http://forums.jce.divched.org:8000/webx?50@@.1adb27a8 (accessed Feb 2008).
Supporting JCE Online Material
http://www.jce.divched.org/Journal/Issues/2008/Apr/abs522_1.html Full text (HTML and PDF) with links to cited URLs
Journal of Chemical Education • Vol. 85 No. 4 April 2008 • www.JCE.DivCHED.org • © Division of Chemical Education
