© Division of Chemical Education  • www.JCE.DivCHED.org  •  Vol. 86 No. 5 May 2009  •  Journal of Chemical Education 577

Chemistry for Everyone

Demonstrations are an effective method to get students interested in and excited about chemistry. Flame tests for certain cations garner “oohs” and “aaahs” from the student audience. Recently, this Journal featured several variations on methanol-fueled flame tests (1–4). In seeking a safe way to show the flame tests for large audiences, we thought using a porous support material that would absorb the methanol solution would be ideal. Trials with balsa wood, soaked overnight in the methanol solutions, produced only the typical yellow flame of sodium when ignited. Similar yellow flames were obtained with pieces of cellulose sponge. Both the wood and sponge, of course, charred as the methanol burned away.

A Mr. Clean Magic Eraser was examined as the porous material, mainly because it was used in the laboratory. We placed pieces of it in the methanol solutions. The pieces were removed from the solution and held securely with crucible tongs. When ignited, the pieces produced the desired flame test colors with-out sodium interference. The flames were extinguished after 30–45 seconds by submersion in a large container of water. The “eraser” material did not char and the pieces could be reused, at least in the short term. When the pieces of the eraser were stored in closed containers of the various methanol solutions for several months, some pieces decomposed in the solutions.

We tested both Mr. Clean Magic Eraser and GV Miracle Cleaning Eraser1 as support material for the flame tests. We found no observable difference between flame duration or color for the two products.

Materials

• Methanol solutionsofLiNO3,KNO3, CuCl2⋅2H2O,Sr(NO3)2,andNaNO3

(Chlorides can be used; however, the nitrates listed are more soluble in methanol.)

• Small wide-mouth closable containers to store eraser pieces and solutions

• Cleaningeraser,cutintocubes • Crucibletongs,onepairpersolution • Grillorcandlelighter • Largecontainerofwater • Darkenedroom • Fireextinguishershouldbeavailable

for any demonstration involving flames.

Preparation and Presentation

The cleaning eraser can be cut to the desired size with a box cutter or scissors. The size can be varied to suit the size of audience or venue. For a large auditorium (250 persons) we used rectangular pieces approximately 2.5 × 2.5 × 4 cm. For the aver-age classroom setting, 1 cm cubes are adequate.

Our testing solutions were prepared by dissolving150–300mgofthesaltinabout8mLofmethanol.Ifthesaltdidnotreadilydissolve,about1mLofwaterwasaddedtofacili-tate dissolution. This volume was sufficient solution to saturate the larger rectangle of the eraser material. Depending on the ability to darken the demonstration area, higher concentration or saturated solutions may be needed for some salts. The eraser pieces can be stored (for several weeks) in their respective solu-tions in closed containers. The containers should be properly labeled including the concentrations and contents.

We suggest labeling a separate pair of clean crucible tongs for each solution to avoid cross-contamination of the flame colors. To demonstrate the flame tests, use tongs to remove the piece of eraser from the container. Press the eraser against the in-side of the container to remove excess solution. The eraser should be wet but not dripping. Close the container and set it aside. Using a candle lighter, ignite the methanol-soaked eraser.

Extinguish the flame after 30–60 seconds but before all of themethanolhasburned.Onceallofthemethanolisconsumed,the flame will become yellow and eraser material will char. The flame is easily extinguished by submerging the eraser in a large container of water. Excess water can be removed from the eraser and the piece can be reused in the same solution (as all the cat-ions are not necessarily removed).

Discussion

Using cleaning erasers as the support material for demon-strating flame tests has several advantages over the hydrogen balloon methods. This method is safer since explosions are avoided. With the precaution of closing the containers holding the methanol solutions, fire risk is minimal. The quantities of salts and methanol involved during the demonstration are small; again reducing the chances of fire.

The color display is longer than obtained by the hydrogen balloon technique. The quantity of metallic salts emitted into the air is very small. We calculated a maximum of 100 mg of salt per 30 seconds of burn time.

“Magic Eraser” Flame Tests

submitted by: Arthur M. Landis* and Malonne I. Davies Departments of Physical Science, Chemistry Department, Emporia State University, Emporia, KS 66801-5087; *alandis@emporia.edu

Linda Landis Science and Mathematics Education Center, Emporia State University, Emporia, KS 66801-5087

checked by: Nicholas C. Thomas Department of Chemistry, Auburn University at Montgomery, Montgomery, AL 36124

JCE DigiDemos: Tested Demonstrations edited by

Ed VitzKutztown University

Kutztown, PA 19530

578 Journal of Chemical Education  •  Vol. 86 No. 5 May 2009  • www.JCE.DivCHED.org  • © Division of Chemical Education

Chemistry for Everyone

We also consider the absence of a loud explosion an ad-vantage. The overarching goal for all our demonstrations is to encourage interest in and learning about science. While some spectators in the audience like the flash bang nature of such demonstrations, some individuals, especially younger children are frightened by the sudden loud noise (even when warned in advance).

Hazards

Safety goggles should be worn during both preparations and presentation of this demonstration. Those observing the demonstration should be at a safe distance from the flames or a safety shield should be used.

Methanol is flammable so any containers containing metha-nol (or other flammable materials) should be closed and moved away from the demonstration area. This includes the contain-ers of methanol solutions used for the demonstration. A fire extinguisher should be readily available for this demonstration. The cleaning erasers should not be exposed to chlorine bleach (sodium hypochlorite solution) or other strong oxidizers.

Note

1. Mr. Clean Magic Eraser is a registered trademark of Procter and Gamble. GV Miracle Cleaning Eraser is manufactured for and sold by Wal-Mart.

Literature Cited

1. Mortier, T; Wellens, A.; Janssens, M-J. J. Chem. Educ. 2008, 85, 522.

2. Thomas,N.C.J. Chem. Educ. 2008, 85, 521. 3. Vitz, E. J. Chem. Educ. 2008, 85, 522. 4. Dragojlovic, V. J. Chem. Educ. 1999, 76, 929.

Supporting JCE Online Materialhttp://www.jce.divched.org/Journal/Issues/2009/May/abs577.html

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