In the Laboratory
A Simple, Transparent Fume Hood John Fredericks Dallas High School, P.O. Box 2000, Dallas, PA 18612
The reaction of copper metal with nitric acid is used in lab exercises (1–3) to investigate the copper cycle, or as a demonstration of a chemical reaction (4 ). The reaction generates toxic NO2 gas and must be performed within a fume hood. However, many high school teachers do not have access to a working fume hood. One substitute for a fume hood is an inverted funnel connected to a water aspirator by vacuum tubing. The funnel is then inverted on top of the reaction beaker to collect the gas as it is produced (1, 5). It has been my experience that some NO2 can still escape into the room, especially if the student has not carefully secured the funnel. An inexpensive alternative is to construct the following device (Fig. 1). A clear plastic two-liter soft drink bottle is cut just above the base. The bottle should be trimmed so that it sits flush on the lab bench. A length of vacuum tubing is sealed to the opening of the bottle using black electrical tape. The tubing is then connected to a water aspirator. Beakers or flasks easily fit inside the bottle, and the bottle may be secured with a clamp and ring stand for added stability. Also, the beaker and plastic soda bottle may be set in a pan of sand and the bottle pushed down into the sand to provide an added seal. My students have safely used this “fume hood” to perform the copper–nitric acid reaction with no trace of NO2 escaping into the classroom. An added benefit is that the clear plastic allows students to view the gas formation from all sides. There are two safety concerns for this device. First, the device should be used only for gases that have significant solubility in water or react with water. (Tables of water solubility can be found in refs 6 and 7.) If a gas has no solubility in water, it will be mechanically removed through the aspirator and enter the atmosphere of the room through the sink.
Vacuum Tubing to water aspirator
Black tape
Plastic Bottle
Figure 1. The fume hood.
Second, the device should not be used for highly exothermic reactions or above a Bunsen burner, because of the flammability of the plastic. Literature Cited 1. Roberts, J. L.; Hollenberg, J. L.; Postma, J. M. Chemistry in the Laboratory, 4th ed.; Freeman: New York, 1997. 2. Nelson, J. H.; Kemp, K. C. Laboratory Experiments for Chemistry The Central Science; Prentice Hall: Upper Saddle River, NJ, 1997. 3. Wentworth, R. A. D. Experiments in General Chemistry, 2nd ed.; Houghton Mifflin: Boston, 1990. 4. Summerlin, L. R.; Borgford, C. L.; Ealy, J. B. Chemical Demonstrations: A Sourcebook For Teachers, 2nd ed., Vol. 2; American Chemical Society: Washington, DC, 1988. 5. Moore, W. D. J. Chem. Educ. 1959, 36, 407. 6. Lange’s Handbook of Chemistry, 14th ed.; Dean, J. A., Ed.; McGraw-Hill: New York, 1992. 7. CRC Handbook of Chemistry and Physics, 71st ed.; Lid, D. R., Ed.; CRC: Boca Raton, FL, 1990.
JChemEd.chem.wisc.edu • Vol. 75 No. 10 October 1998 • Journal of Chemical Education
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