In the Classroom edited by
JCE DigiDemos: Tested Demonstrations
Ed Vitz Kutztown University Kutztown, PA 19530
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A Methane Balloon Inflation Chamber submitted by:
Curtis J. Czerwinski* and Tanya J. Cordes Department of Chemistry, University of Wisconsin–La Crosse, La Crosse, WI 54601; *
[email protected] checked by:
Joe Franek Department of Chemistry, University of Minnesota, Minneapolis, MN 55455
The detonation of a hydrogen-filled balloon is one of the most dramatic and commonly used demonstrations in general chemistry lectures (1). While hydrogen gas cylinders for inflating balloons are available in most chemistry departments their dedication to hydrogenation equipment or gas chromatographs often presents an inconvenience for the demonstrator who must disconnect and reconnect laboratory equipment to inflate a balloon. For some demonstrations methane may be an appropriate alternative to hydrogen, especially since it appears to be so readily available from the gas outlets in laboratories and many lecture halls. A problem with this alternative though, is that the pressure from these gas outlets is too low to inflate a balloon. To get around this problem without buying a high-pressure methane gas cylinder, several techniques for filling containers with methane for detonation demonstrations have been suggested, including suction-bulb inflation of a balloon, formation of methanefilled soap bubbles, explosion of methane collected in a tin can, and the very dangerous low-temperature collection of liquid methane that is burned as it subsequently vaporizes upon warming (2–6). We describe a device for inflating a methane balloon using a standard methane outlet in a laboratory or lecture hall. The device is fast, safe, inexpensive, and easy to use. Equipment • High-density polyethylene pail, such as the 5-gallon utility pails often found in painting sundries departments of home improvement stores. While a standard, opaque pail may be adequate, the recommended pail is a 3.5-gallon translucent pail manufactured by Encore Plastics Corporation (7). The pail should have a tightly fitting “Leaktite” lid with a rubber gasket. • Cork borer, 21-mm (3/4-inch) diameter. • Two hollow plastic, glass, or copper tubes (∼10-cm long × 80-mm o.d.) each inserted into a #3 one-hole rubber stopper. • A #5 one-hole rubber stopper. • Thick-walled rubber tubing, 6.4-mm i.d. × 4.8-mm wall thickness × 1.5–2.0-m long, to fit tightly around the plastic, glass, or copper tubes (or example, Fisher catalog # 14-150-2J).
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• Thin-walled rubber tubing, amber or black, 6.4-mm i.d. × 1.6-mm wall thickness × 1.5–2.0-m long (for example, Fisher catalog # 14-178-2C). • Pinch clamp for thin-walled rubber tubing (for example, Fisher catalog # 05-867). • Balloon, “12-inch round.” The balloon will be ∼15cm long before inflation and have a ∼30-cm diameter when inflated. • Access to methane gas outlet and vacuum source such as house-vacuum or a water-aspirator connection.
Procedure The methane balloon inflation chamber is constructed from a 3.5- or 5-gallon translucent plastic pail by making modifications to its tightly fitting lid. Using the 21-mm cork borer, bore a hole near the center of the lid, and a second hole approximately 8 cm from the edge of the lid. Place a #3 one-hole rubber stopper, with a copper, glass, or plastic tube already inserted, into each hole in the lid. Use thick-walled rubber tubing to connect a house-vacuum outlet or wateraspirator nozzle to the top of the tube that is near the edge, and use thin-walled rubber tubing to connect the methane gas outlet to the tube in the center of the lid. Around the bottom part of this second tube, where methane will be entering the balloon inside the pail, attach a #5 stopper with its wide end away from the lid. Slip the mouth of the balloon over this stopper, so the slope of the stopper holds the balloon in place during inflation. Seal the lid completely and turn on the methane so that when vacuum is applied methane will fill the balloon to the desired size. If the pail is translucent the balloon will be observable throughout the process so the demonstrator will know when to stop filling and, if desired, the audience will also be able to watch the inflation. When the balloon has been inflated to the desired size, turn off the methane and vacuum (it may be necessary to remove one of the stoppers to vent the pail if a slight vacuum still exists), and clamp the thin-walled tubing. Remove the lid from the pail, pinch the neck of the balloon, detach it from the #5 stopper, and tie it closed (Figure 1; a color image of the inflation chamber appears in the table of contents of this issue). If a long piece of thread or dental floss is tied to the balloon (string is too heavy) it can be anchored away from
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In the Classroom thin-walled tubing from gas outlet thick-walled tubing to vacuum or aspirator tightly fitting pail lid
Figure 1. Inflation chamber for filling a methane balloon under reduced pressure.
#5 rubber stopper #3 rubber stoppers
3.5-gallon translucent pail
balloon to be inflated
any other flammable items and at least ten feet away from audience members in a lecture hall before ignition with a burner or burning candle attached to the end of a meter stick. Because of the associated sound intensity, be sure to warn audience members to cover their ears before this or any other detonation demonstration (8, 9). The demonstrator should also wear hearing protection and safety goggles. Another novel and somewhat dramatic demonstration can be accomplished using the inflation chamber to inflate a balloon using suction. Attach a deflated balloon to the filling port inside the pail and clamp the thin-walled tubing, making sure its other end is free (not attached to a gas port.) Seal the lid and apply vacuum. The volume of the balloon will not appear to change, but when the vacuum is turned off and the clamp removed air will rush in to inflate the balloon. When the tubing is clamped and the lid taken off the pail, the balloon can be removed and tied shut, thus completing a “balloon inflation by vacuum.” Discussion After its initial preparation, the inflation chamber should provide a fast and convenient tool for use in college and high school general chemistry lectures and chemistry demonstrations shows. We have used the methane balloon in many of the same situations where the hydrogen balloon can be used, mostly for illustrating combustion reactions and exothermic processes. Also, for demonstrating the densities of a series of gases, a methane-filled balloon provides an excellent example of a gas whose density lies between the obvious “floaters” hydrogen and helium, and the obvious “sinkers” oxygen and carbon dioxide. This point is well illustrated when a methane balloon sinks when tied with heavy string but floats when tied with lightweight thread. The inflation chamber is especially useful here since these density comparisons are most conveniently demonstrated using balloons rather than other vessels. We have also used the inflation chamber to inflate propane balloons by stretching the thin-walled tubing around the mouth of a handheld propane “blow torch,” which would
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otherwise have a pressure too low to inflate balloons outside the inflation chamber. In the absence of readily accessible vacuum or aspirator connections, we have found that a shopvac or handheld vacuum cleaner works just as well in evacuating the inflation chamber. Methane balloon inflation might also be accomplished under reduced pressure inside a bell jar, but most bell jars that are big enough for the required size of balloon are made of thick-walled glass and are heavy, expensive, and breakable. Durable lightweight plastic bell jars are available from science supply companies but they typically sell for around $90, and have a maximum volume of only 5 liters. The translucent pail alternative described here is lightweight, inexpensive, and durable. Furthermore, the ability to clamp the thin-walled tubing and remove the balloon through the wide mouth of the pail is what makes this method work for large “lecture-sized” balloons in a way that a typical bell jar setup would not. While an opaque pail could be used to accomplish the same end results, the best pail for this demonstration is translucent, allowing both the demonstrator and audience to see how big the balloon is getting during inflation. While completely transparent pails are not commercially available in large enough sizes, blue, yellow, or purple tinted translucent pails in 3.5-gallon sizes from Encore Plastics Corporation are available at many local discount and home improvement stores. These pails are large enough for inflating balloons to convenient sizes, and rigid enough to withstand aspirator or house-vacuum pressure, though some “flexing” of the pail and lid will be observed during inflation. We have found that the rigidity of a brand new lid can be somewhat cumbersome at first, but after a few uses it gets “broken-in” and becomes more convenient to use in front of an audience, while its seal is still able to maintain a reduced-pressure atmosphere inside the pail. Be sure to remove completely the original plastic seal ring around the lip of the lid before using it, and use fresh rubber stoppers and lengths of tubing that are free of cracks. When using a translucent pail, we have found the best color choices for clearly seeing balloons during inflation are dark blue or purple balloons with a yellow translucent pail.
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In the Classroom
Hazards
Literature Cited
Owing to its high flammability, methane presents a fire and burn hazard when used in this or any other demonstration. The demonstrator must be aware of these potential hazards even if the balloon is used in a nondetonating demonstration, such as that of gas density. If the inflated methane balloon is to be detonated, the demonstrator, who should already be wearing safety goggles, should only detonate the balloon using a candle or burner that is attached to a very long stick. The balloon should only be used at least ten feet away from nearest audience members. As with any detonation demonstration, the demonstrator has a responsibility to warn the audience of the extremely loud noise and potentially large flame accompanying the explosion. The demonstrator should also wear hearing protection and safety goggles. Special precautions must always be followed when transporting balloons filled with any flammable gas, and it is recommended that a device such as the inflation chamber described here be used to inflate balloons on-site for chemical demonstrations (10).
1. Shakashiri, B. Z. Chemical Demonstrations: A Handbook for Teachers of Chemistry; University of Wisconsin Press: Madison, WI, 1983; Vol. 1, pp 106–112. 2. Corkern, Walter H.; Hughes, Elvin, Jr. J. Chem. Educ. 1999, 76, 794. 3. Summerlin, L. R.; Ealy, J. L., Jr. Chemical Demonstrations, A Sourcebook for Teachers; American Chemical Society: Washington, DC, 1985; p 7. 4. Herr, N.; Cunningham, J. Off-gassing. http://www.csun.edu/ ~vceed002/BFI/lessons/offgassing.html (accessed Sep 2004). 5. Willey, D. A Dozen Dynamite Demonstrations. http:// www.pitt.edu/~dwilley/SevenSprings/SevenSprings.html (accessed Sep 2004). 6. Bodner, G. M. J. Chem. Educ. 1985, 62, 1105–1107. 7. Encore Plastics Corporation is located at 230 W. Main Street, Bellevue, OH, 44811 or can be contacted through their Web site. http://www.e-encore.com/31448.htm (accessed Sep 2004). The pails are available for $3.29 (as of summer 2003) at Sutherlands Lumber and Home Improvement Centers, http:// www.sutherlands.com/ (accessed Sep 2004). 8. McNaught, Ian J. J. Chem. Educ. 1998, 75, 52. 9. Battino, R.; Battino, B. S.; Scharlin, P. J. Chem. Educ. 1992, 69, 921–923. 10. Garrett, G. J. Chem. Educ. 2003, 80, 743.
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Supplemental Material
There is a video showing an explosion of a balloon containing pure methane and an explosion of a balloon containing methane and oxygen available in this issue of JCE Online.
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