Demonstration pubs.acs.org/jchemeduc
Climate Change: A Demonstration with a Teaching Moment Steven Murov* Division of Science, Mathematics and Engineering, Modesto Junior College, Modesto, California 95350, United States ABSTRACT: Experience from audience reactions indicates that most people cannot name the three most abundant gases in dry air. As this is relevant for an understanding of climate change, a demonstration involving mass determinations of equal volumes of four gases is provided to help the public understand that human activity is capable of increasing the carbon dioxide content of the atmosphere.
KEYWORDS: High School/Introductory Chemistry, First-Year Undergraduate/General, General Public, Demonstrations, Public Understanding/Outreach, Environmental Chemistry, Problem Solving/Decision Making, Atmospheric Chemistry, Gases
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observations can be made and conclusions can be reached. The masses of the bottles will come out close to the values 2.24 g, 2.17 g, 2.48 g, and 3.41 g respectively for the air, nitrogen, oxygen, and CO2. The bottles will maintain their masses for many weeks although the CO2 bottle eventually will collapse. Consistent with expectations, the mass of the air comes out a little above the mass of nitrogen and between the masses of nitrogen and oxygen. The mass measurements demonstrate that air does not contain much CO2. As an added discussion topic that demonstrates the huge density difference between solids and gases, the mass of the gas in the 1.89 L container can be compared to the approximately 2.5 g mass of a penny.
ecause anthropogenic climate change could provide one of the biggest challenges ever confronted by society, it is extremely important that students strive for climate science literacy. The subject of anthropogenic climate change is extremely complex, and predictions depend on ever-improving computer modeling that most people should not be expected to comprehend. However, familiarity with some of the basics helps people evaluate the evidence presented by the proponents and the deniers. One example from my experience with lay audiences of all ages is that very few people, when asked, can name the three most abundant gases in dry air.1 Most people name oxygen, some name nitrogen, almost none name argon, and many include CO2 among the top three. This paper describes a demonstration that should lead to the conclusion that there is not much CO2 in the air and a brief discussion of how this concept can help people understand that humans are contributing to an increase of CO2 in the atmosphere. This demonstration is appropriate for people 10 years old and up. The demonstration can be performed in a few minutes and should be followed by a discussion at an appropriate level for the type of audience.
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HAZARDS The gases used to fill the bottles for weighing, namely, air, nitrogen, oxygen, and CO2, are not toxic.
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DISCUSSION The relevance of this demonstration is that the public is told that fossil fuel combustion is increasing the CO2 content of the atmosphere, but it is difficult for many to understand how human activity could conceivably change the atmospheric composition. If it is recognized that CO2 is only about 0.04% of the atmosphere, it should help the public understand that human activity has been able to increase the CO2 by a quantity approaching 40%. Because the atmospheric CO2 content is low, the current annual production of CO2 of 31.5 gigatonnes from combustion4 amounts to about 1% of the CO2 content of the atmosphere (total of about 3,000 gigatonnes of CO2).5 Not all of the annual production of CO2 stays in the atmosphere (e.g., the oceans absorb a substantial quantity, and the resultant pH
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DEMONSTRATION One method of providing evidence of the low atmospheric content of CO2 is to provide four, two-quart plastic juice bottles (1.89 L and about 85 g each) that have had their empty masses (cap included) adjusted to 102.24 g by the addition of about 15 g of masses and removal of pieces of the labels.2 Because the air in the 1.89 L container at 25 °C has a mass close to 2.24 g, the mass over 100.00 g is the mass of the gas in the bottle. One of the bottles is sealed, thus containing air. The air in the remaining three bottles is displaced with nitrogen, oxygen, and CO2, respectively, and sealed. The bottles can then be weighed on an electronic centigram scale3 to sufficient precision that © XXXX American Chemical Society and Division of Chemical Education, Inc.
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dx.doi.org/10.1021/ed400363u | J. Chem. Educ. XXXX, XXX, XXX−XXX
Journal of Chemical Education
Demonstration
drop could be a significant threat to the ocean ecology).6 However, over a couple hundred years of the industrial revolution, combustion has caused a 40% increase in the CO2 content of the atmosphere. Although this demonstration does not provide evidence that CO2 affects the global climate, it does provide a significant first step in helping the public understand that humans are capable of changing our atmosphere. For people stimulated to improve their climate science literacy, many references are available by using the Internet to search for climate change and related topics. In addition, a Web site with many of the most pertinent references has been posted.7
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Pidwerny, M. Atmospheric Composition, May 7, 2009. http:// www.physicalgeography.net/fundamentals/7a.html (accessed Jun 2013) (2) For more details, visit: Murov, S. Water, Density and Metrics. http://murov.info/waterexhibit.pdf (accessed Jun 2013). (3) A very reasonably priced 200 g capacity electronic scale with 0.01 g readability (My Weigh i201-P78) is available at: http://www. oldwillknottscales.com/my-weigh-ibalance-201.html (priced at $118 when accessed in Jun 2013). (4) International Energy Agency, 2012. http://www.iea.org/ newsroomandevents/news/2012/may/name,27216,en.html (accessed Jun 2013). (5) Carbon Dioxide, from Wikipedia, 2012, http://en.wikipedia.org/ wiki/Carbon_dioxide (accessed Jun 2013). (6) NOAA. http://www.pmel.noaa.gov/co2/story/ Ocean+Acidification (accessed Jun 2013). (7) Murov, S., Climate Change Directory, 2012. http://murov.info/ climatechange.htm (accessed Jun 2013).
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dx.doi.org/10.1021/ed400363u | J. Chem. Educ. XXXX, XXX, XXX−XXX
