In the Classroom edited by
JCE DigiDemos: Tested Demonstrations
Ed Vitz
Kutztown University Kutztown, PA 19530
Flames Tests with Flair submitted by:
checked by:
Nicholas C. Thomas Department of Chemistry, Auburn University Montgomery, Montgomery, AL 36124-4023;
[email protected] Kenneth S. Lyle Department of Chemistry, Duke University, Durham, NC 27708-0354
Sheldon Knoespel Department of Chemistry, Michigan State University, East Lansing, MI 48824-1322
Exploding rubber balloons filled with hydrogen has long been a popular demonstration to both observe and perform, and many variations on the procedure have been previously published (1–3). For instance, adding several grams of solid metal salts to the balloon prior to inflation has been shown to impart colors to the flames (3). While effective, this procedure can produce smoke and fumes and risks ejection of incompletely burned solids. An alternative procedure offered here involves spraying a 5% aqueous solution of metal salts onto the outer surface of the inflated balloon prior to ignition. This method uses much less material and is safer, cleaner, and quite effective in demonstrating flame tests.
solutions. Balloons may be ignited immediately, while still wet, or later with a fine layer of the dried solid salt adhering to the balloon’s surface. Spraying the balloons with metal salt solutions is an easy and effective way to distribute the salts over a large surface area. With this method, just 0.05 g of metal salt is deposited on the balloon’s surface for each one milliliter of 5% solution used, which is far less than the alternative method (3). Upon combustion, the metal ions are rapidly vaporized to produce the expected characteristic colors.
Materials
Wear safety goggles when filling and handling balloons with hydrogen. Static discharges can accidently ignite the balloons, and hydrogen-filled balloons should not be stored or transported in large plastic bags (4). The demonstration should be conducted in a large, properly ventilated fume hood or outdoors.
• Rubber balloons inflated with hydrogen
• Atomizer spray bottles filled with 5% aqueous metal salt solution, for example, LiCl, NaCl, KCl, or CuCl2⋅2H2O (The use of salts containing highly toxic metals, such as barium, should be avoided.)
• Meter ruler with candle attached at one end
Flame Test Demonstration Balloons should be inflated with hydrogen to a diameter of about 6 inches and secured with a short piece of string in a large fume hood. If the demonstration is conducted outdoors, balloons can be inflated up to a diameter of about 10 inches. Each balloon is then sprayed with a fine mist of metal salt solution from an atomizer spray bottle containing 5% aqueous metal
Hazards
Literature Cited
1. 2. 3. 4.
Hartman, N. T. J. Chem. Educ. 2003, 80, 774. Lawrence, S. S.; Franz, D. J. Chem. Educ. 1995, 72, 177. Fortman, J. J. J. Chem. Educ. 1991, 68, 937. Garrett, G. J. Chem. Educ. 2003, 80, 743.
Supporting JCE Online Material
http://www.jce.divched.org/Journal/Issues/2008/Apr/abs521.html Abstract and keywords Full text (PDF) with links to cited JCE articles
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 85 No. 4 April 2008 • Journal of Chemical Education
521
