In the Laboratory edited by
Erica K. Jacobsen Laura E. Slocum
Another Look at the Fizz Keeper: A Case-Study Laboratory Exercise for High School Students Christopher R. Mekelburg and Steven H. Szczepankiewicz* Department of Chemistry and Biochemistry, Canisius College, Buffalo, New York 14208 *
[email protected] Matthew Hellerer Science Department, St. Joseph's Collegiate Institute, Buffalo, New York 14223
Case-study learning uses a story to engage students in content-based material (1, 2). This effective strategy in undergraduate chemical education can also be applied at the high school level to enable students to connect classroom concepts with the outside world. This case study expands on a Journal article written by Howald (3) about the Fizz Keeper (Steven Spangler Science), a device marketed to improve carbonation in previously opened bottles of soft drink. The manufacturers of the Fizz Keeper claim “if the open volume within the beverage container is re-pressurized with ambient air, the amount of dissolved carbon dioxide released from the beverage will [be] substantially reduced” (4). However, this premise can lead to misconceptions about LeCh^atelier's principle, a topic identified as one of the most difficult to teach in high school chemistry.1 The equilibrium due to carbonation inside of a bottle of carbonated soft drink is CO2 ðgÞ h CO2 ðaqÞ ð1Þ According to LeCh^atelier's principle, a change in pressure will only affect the equilibrium if there is a change in the partial pressure or gas-phase concentration of one of the gases present in the equilibrium expression: ½CO2 ðaqÞ ð2Þ Keq ¼ ½CO2 ðgÞ The common misconception addressed in this exercise is that an increase in overall pressure will affect the carbonation equilibrium. The Fizz Keeper increases the total pressure of the system by adding air, which is composed mainly of nitrogen and oxygen. The total pressure is defined as the sum of the partial pressures Ptotal ¼ PN2 þ PO2 þ PCO2 þ :::
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The partial pressure of carbon dioxide within the bottle changes minimally as the total pressure increases because air contains very little carbon dioxide (less than 0.1%). The equilibrium is unaffected, because carbon dioxide is the only gas appearing in the equilibrium expression (eq 2). The Fizz Keeper does not affect the equilibrium concentration of carbon dioxide in the aqueous phase and neither preserves nor restores original carbonation levels to the drink. The Fizz Keeper retains carbonation levels for a short period of time until the new equilibrium is reached as described previously (3). The rate at which the new equilibrium is reached is slowed by increasing the pressure above the aqueous layer, thus retaining carbonation for minutes and hours, but not for days or
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weeks. The procedure for this laboratory case study minimizes this kinetic effect, and thus focuses on LeCh^atelier's principle, which is more appropriate for an introductory chemistry laboratory course. Summary of The Fizzy Forcer Case Study Carbonation Creators,2 the producer of the Fizzy Forcer (a fictitious name for a device to improve carbonation in previously opened bottles of soft drinks), is facing a lawsuit from Tyler, Makar, and Thomas,2 a law firm specializing in classaction lawsuits. Tyler, Makar, and Thomas represents people who believe that the Fizzy Forcer does not work. The student acting as a chemist has been hired by Carbonation Creators to defend their product. In a letter describing the details of the lawsuit, the CEO of Carbonation Creators describes how the Fizzy Forcer is scientifically designed to work based on LeCh^atelier's principle. The student is then asked to test the product to confirm that it retains carbonation levels in previously opened bottles of soft drink. The student is guided with a visually based laboratory procedure. Students develop an understanding of LeCh^atelier's principle while disproving Carbonation Creators' claim. The successful student will discover that the product does not work and that the company has incorrectly interpreted LeCh^atelier's principle; that is, an increase in pressure only affects the carbon dioxide gas/ aqueous equilibrium if it increases the partial pressure of carbon dioxide gas. Effective science education addresses student misconceptions (5). Methods such as guided inquiry enable students to reevaluate their understanding (5). Therefore, the exercise embraces the idea that the Fizzy Forcer should work as described. Implementation of the case study confirms that students generally agree with this premise until the experimental data fail to support their preconception. The case study was written for an introductory high school chemistry course, as well as for an advanced placement or general chemistry undergraduate equivalent course. The Fizzy Forcer case study is consistent with both the New York State Regents chemistry requirements (6) and the College Board Advanced Placement chemistry curriculum (7) and targets topics found in most general introductory chemistry classrooms. The laboratory versions can be used independently. The laboratory exercise requires 10-15 min to prepare the samples and 45-60 min to test the samples. The complete case and laboratory exercise are available in the supporting information.
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r 2010 American Chemical Society and Division of Chemical Education, Inc. pubs.acs.org/jchemeduc Vol. 87 No. 7 July 2010 10.1021/ed100297p Published on Web 04/28/2010
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In the Laboratory
Figure 2. Comparison of concentrations of carbon dioxide of various soft drink samples. Fresh samples (dark gray) were opened for the first time and immediately tested. Recapped samples (medium gray) were opened for 30 min, sealed with the original bottle cap, and allowed to equilibrate for 24 h before testing. Repressurized samples (light gray) were opened for 30 min, sealed and pumped with the Fizz Keeper, and allowed to equilibrate for 24 h before testing.
Figure 1. Apparatus to measure soft drink carbonation.
Experimental Summary A variety of methods have been suggested to measure the carbonation in a bottle of soft drink (8-11). Visual examples are essential to student understanding of any given science topic (12) and can aid in the prevention of misunderstanding (13). In this experiment, students observe carbon dioxide escaping from the soft drink. Students test samples of soft drink from three sources: a freshly opened bottle; a bottle that has been left open for 30 min and then recapped and allowed to reach a new equilibrium; and a bottle that has been left open for 30 min and then repressurized with the Fizzy Forcer and allowed to reach a new equilibrium. The apparatus to measure carbonation (Figure 1) is suitable and affordable3 and has been demonstrated to be effective in a high school. Students seal a known volume of soft drink in a large test tube with a bored rubber stopper. A piece of rubber tubing connects the stopper to a T-adapter containing a solution of dish soap. One opening on the T-adapter is sealed with a rubber bulb, and the other is connected to a long glass measuring tube (such as a buret without the stopcock). The carbon dioxide released from the beverage passes through the tubing and soap solution, forming a column of soap bubbles that rises into the measuring tube. Heating the soft drink drives the equilibrium toward the gaseous phase, illustrating another example of LeCh^atelier's principle. All three soft drink samples are heated simultaneously in the same water bath, and the volume of carbon dioxide gas produced is measured using three separate glass tubes. The volume of gas produced depends upon the carbonation level of the sample and the degree of heating, and therefore indicates the relative quantities of carbonation in the samples. When the gas production slows, the test tubes are removed from the water bath and placed in an ice bath to cool down. 706
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Students assume the system is stressed to completion such that the volume of soap bubbles measured in the tube directly relates to the amount of carbon dioxide originally dissolved in the soft drink. The ideal gas law shows the relationship between the volume of soap bubbles and the number of moles of carbon dioxide. The calculated moles divided by the volume of soft drink gives the molar concentration of carbon dioxide originally present in the samples. Students comment on the effectiveness of the Fizzy Forcer by comparing the molar concentrations of the three samples. This procedure was tested using a focus group of high school students, as well as within an undergraduate analytical chemistry lab course, and the refined experiment was implemented in a high school setting. Observations and instructor recommendations are described in detail in the troubleshooting section of the supporting information. Data from the laboratory exercise appear in Figure 2. Each trial represents the analysis of one experimental set containing fresh, recapped, and repressurized soft drink samples. The fresh samples typically have about twice the carbon dioxide concentration of the others. The recapped and repressurzied samples are of similar carbonation levels. Neither condition results in a consistently higher concentration, leading to the conclusion that there is no difference between the recapped and repressurized samples. This conclusion is clear from the graphical data and is also supported by single factor ANOVA statistical analysis. Hazards The Fizz Keeper pumps may be propelled from the bottle if excessive pressure is applied. There are no significant contact hazards. Standard laboratory practice such as the use of goggles and caution with heat is necessary. Conclusion The case-study method forces students to recognize their misconceptions. The use of a visual example also aids in student understanding. The Fizzy Forcer case study addresses a variety of topics including LeCh^atelier's principle, Henry's law, openversus-closed systems in equilibrium, scientific handling of data,
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In the Laboratory
and scientific evaluation of data. High school students are able to carry out the lab successfully. The case available in the supporting information is written in a general form and can be adapted to a variety of classroom situations. Acknowledgment Photographs courtesy of Kerri Nowak. Notes 1. Results of an unpublished survey of teachers in the Buffalo, New York, area conducted by Mekelburg and Szczepankiewicz in May 2008. 2. Carbonation Creators and Tyler, Makar, and Thomas are fictional entities. 3. The Fizz Keeper is also affordable and has a variety of other uses in the chemistry classroom (14).
Supporting Information Available
Literature Cited 1. Dinan, F. J.; Szczepankiewicz, S. H.; Carnahan, M.; Colvin, M. T. J. Chem. Educ. 2007, 84, 617.
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2. Herreid, C. F. J. Coll. Sci. Teach. 1997, 27, 92. 3. Howald, R. J. Chem. Educ. 1999, 76, 208. 4. Robinson, T. R.; Beyer, M. B. Pump Closure for Carbonated Beverage Container. U.S. Patent 4,723,670. Feb 9, 1988. 5. Horton, C. Calif. J. Sci. Educ. 2007, 7 (2), 103. 6. New York State Education Department Core Curriculum Home Page. http://www.emsc.nysed.gov/ciai/ (accessed April 2010). 7. College Board AP: Chemistry. http://www.collegeboard.com/ student/testing/ap/sub_chem.html?chem (accessed April 2010). 8. De Grys, H. J. Chem. Educ. 2007, 84, 1117. 9. Rohrig, B. ChemMatters 2002, 20 (1), 11. 10. Glasser, L. J. Chem. Educ. 2008, 85, 47. 11. Official Methods of Analysis of the Association of Official Analytical Chemists; Horwitz, W., Ed.; Association of Official Analytical Chemists: Washington, DC, 1980; p 191. 12. Gilbert, J. K. Visualization in Science Education; Springer: Dordrecht, The Netherlands, 2007. 13. Gabel, D. J. Chem. Educ. 1999, 76, 548. 14. Van Natta, S.; Knipp, R. J.; Williams, J. P. J. Chem. Educ. 2005, 82, 1454.
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Complete case and laboratory exercise; observations and instructor recommendations. This material is available via the Internet at http:// pubs.acs.org.
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