In the Classroom edited by
Tested Demonstrations
Ed Vitz
A Dramatic Flame Test Demonstration submitted by:
Kristin A. Johnson and Rodney Schreiner* Department of Chemistry, University of Wisconsin–Madison, Madison, WI 53706; *
[email protected] checked by:
Jon Loring Department of Chemistry, Kutztown University, Kutztown, PA 19530
Kutztown University Kutztown, PA 19530
Flame tests are impressive demonstrations that are often used in lectures during the discussion of atomic structure. Over the years, a large number of variations on the classic flame test technique have been described in this Journal (1– 11). Dalby and Mosher (3) describe a procedure in which aqueous solutions of salts are sprayed into the air intake of a burner. Here, we describe a variation on that procedure, using spray bottles filled with methanol and a variety of salts to produce a brilliantly colored flame. When the methanol/salt solution is sprayed into the flame of a Meker burner, a spectacular ball of colored fire forms that is easily visible in even very large lecture halls. Although the fireball has a short duration compared to flame tests obtained by other methods (1–3), it can easily be recreated by repeated spraying of the salt/methanol solution into the burner. In addition, the spray bottles used in this demonstration are easy to prepare and store.
the colored fireball lasts only Table 1. Flame Colors of about a second, repeated spraying Representative Salt/Methanol Solutions of the methanol/salt mixture into the flame can easily regenerate it. Compound Flame Color A list of the representative colors NaCl Yellow when various salts are ignited is SrCl Red-orange 2 shown in Table 1. LiCl Red The spray bottles containing K C l Violet the salt/methanol solutions are Green simply stored on a shelf between CuCl2 uses. Occasionally, the nozzle of CaCl2 Red-orange the spray bottle will become H BO Green 3 3 plugged with salt after the methanol has evaporated. The salt can be removed by flushing the nozzle and sprayer with water.
Materials
This demonstration should be performed only in a wellventilated room or in a fume hood. The small amount of salt in the spray forms smoke that should not be inhaled. Not all the methanol that is sprayed into the burner flame ignites, resulting in a film of flammable methanol forming near the burner. Do not have any flammable materials within half a meter of the burner. Additionally, never aim the spray directly towards the audience. The audience should be kept at least 2 meters from the flame.
1400 mL methanol 7 spray bottles, 8 oz. (purchased from Fisher Scientific Education, Burr Ridge, IL) 5 g each of NaCl, SrCl2, LiCl, KCl, CuCl 2⭈2H 2O, CaCl2⭈2H2O, and H3BO3 Meker burner flame-proof bench top or 1 × 0.5-m fireproof board
Preparation Add 5 g of each salt to a spray bottle and fill the bottle with methanol. If the bottom of the intake tube on the spray bottle rests on the bottom of the bottle, it can become clogged with undissolved salt. This is especially the true for the NaCl and KCl bottles, since these salts are sparingly soluble in methanol. Trim the intake tube so that the end of the tube is approximately 1 cm above the bottom of the spray bottle. Adjust the nozzle of each spray bottle to create the finest mist possible.
Hazards
Literature Cited 1. Dragojlovic, V. J. Chem. Educ. 1999, 76, 929. 2. McKelvy, G. M. J. Chem. Educ. 1998, 75, 55.
Procedure Perform this demonstration only in a well-ventilated room or in a fume hood. Light a Meker burner and place it on a flame-proof bench top or board. Dim the room lights and spray the solution into the burner flame. The mist will ignite to form a large ball of colored fire (Fig. 1). Although 640
Figure 1. Fireball created when a solution of methanol and potassium chloride is sprayed into a lit Meker burner.
Journal of Chemical Education • Vol. 78 No. 5 May 2001 • JChemEd.chem.wisc.edu
In the Classroom 3. 4. 5. 6. 7.
Dalby, D. K. J. Chem. Educ. 1996, 73, 80. Smith, E. T. J. Chem. Educ. 1995, 72, 828. McRae, R. A.; Jones, R. F. J. Chem. Educ. 1994, 71, 68. Thomas, N. C.; Brown, R. J. Chem. Educ. 1992, 69, 326. Ragsdale, R. O.; Driscoll, J. A. J. Chem. Educ. 1992, 69, 828.
8. Barnes, Z. K. J. Chem. Educ. 1991, 68, 246. 9. Mattson, B. M.; Snipp, R. L.; Michels, G. D. J. Chem. Educ. 1990, 67, 791. 10. Gouge, E. M. A. J. Chem. Educ. 1988, 65, 544. 11. Ager, D. J.; East, M. B.; Miller, R. A. J. Chem. Educ. 1988, 65, 545.
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