In the Classroom edited by
JCE DigiDemos: Tested Demonstrations
Ed Vitz Kutztown University Kutztown, PA 19530
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Carbon Dioxide Fountain submitted by:
Seong-Joo Kang* and Eun-Hee Ryu Department of Chemistry Education, Korea National University of Education, Cheongwon, Chungbuk 3363-792, Republic of South Korea; *
[email protected] checked by:
Mark Case Emmaus High School, 500 Macungie Ave, Emmaus, PA 18049
Demonstrations are interesting. They grab students’ attention and can provide concrete examples of abstract concepts. The ammonia fountain is a classic demonstration that has been a popular experiment for decades. This experiment is pertinent to the students’ understanding of solubility of gases, acid–base interactions, matter flow by pressure difference, and other concepts (1–6). An HCl fountain is also a known demonstration, but no description of a carbon dioxide fountain has been published. In connection with our ongoing effort to develop chemical demonstrations, we have developed the carbon dioxide fountain using consumer chemicals. Alka-Seltzer is often taken for acid indigestion. The active ingredients in Alka-Seltzer are sodium bicarbonate, citric acid, and aspirin. When an Alka-Seltzer tablet is dissolved in water, sodium bicarbonate reacts with acid to generate carbon dioxide gas (7, 8): 3NaHCO3(aq) + H3C6H5O7(aq) citric acid 3CO2(g) + 3H2O + Na3C6H5O7(aq)
NaHCO3(aq) + HC 9H7 O4(aq) aspirin CO2(g) + H2O + NaC 9H7 O4(aq)
These reactions are used as a carbon dioxide gas source in the demonstration of the carbon dioxide fountain. In a closed system, the dissolution of carbon dioxide into alkaline hydroxide solution, as described by the following equations, results in a pressure decrease: 2NaOH(aq) + CO2(g)
ter and two Alka-Seltzer tablets are added to the filter flask and the flask is closed with a solid rubber stopper. A onehole rubber stopper is prepared for the 500 mL round-bottom flask. A glass tube, which goes almost to the bottom of the flask, is inserted in to the stopper and is attached to a 30 cm length of rubber hose. The round-bottom flask is filled with the generated carbon dioxide and then 30 mL of 2.0 M NaOH solution is added to the round-bottom flask. The round-bottom flask is quickly closed with the one-hole rubber stopper and a pinch-clamp is used on the rubber hose to prevent carbon dioxide from escaping. The round-bottom flask is carefully inverted and clamped to a ring stand. A 500 mL beaker containing 400 mL of water and small quantity of bromothymol blue indicator is placed below the roundbottom flask and the rubber hose from the flask is submerged under the water surface in the beaker (Figure 1). After several minutes, the pinch-clamp on the rubber hose is unscrewed. The fountain is observed immediately.
Measurement of the Pressure Decline Using a Gas Pressure Sensor A 40 cm length of rubber hose is attached to the outlet of a 250 mL filter flask and the other end is placed in a 500 mL round-bottom flask. Water, 10 mL, and bromothymol blue indicator are added to the round-bottom flask. Then about 50 mL of 1.0 M HCl solution and five Alka-Seltzer tablets are added to the filter flask and the flask is closed with a solid rubber stopper. A two-hole rubber stopper for the 500
Na2CO3(aq) + H2O
Na2CO3(aq) + H2O + CO2(g)
2NaHCO3(aq)
The decrease in pressure is the driving force for the carbon dioxide fountain. As the gas dissolves in the alkaline solution reducing its pressure, water is driven by atmospheric pressure up from the beaker through the glass tube creating the fountain effect. Experimental Procedures
Carbon Dioxide Fountain A 40 cm length of rubber hose is attached to the outlet of a 250 mL filter flask and the other end of the hose is placed in a 500 mL round-bottom flask. Then about 25 mL of wawww.JCE.DivCHED.org
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Figure 1. Schematic of the carbon dioxide fountain.
Vol. 84 No. 10 October 2007
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Journal of Chemical Education
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In the Classroom
Figure 3. A pressure versus time curve for the reaction between carbon dioxide and NaOH solution.
Figure 2. Schematic of the carbon dioxide fountain using a pressure sensor.
mL round-bottom flask is prepared: in one hole a glass tube that goes half way to the bottom of the flask is inserted and in the second hole a glass tube that reaches just below the stopper is inserted. A 15 cm length of rubber hose is attached to the short glass tube and a 40 cm length is attached to the long glass tube. The 40 cm length of rubber hose is closed with a pinch-clamp and the 15 cm length of rubber hose is connected to a pressure sensor. The round-bottom flask is filled with the generated carbon dioxide and then 50 mL of 2.0 M NaOH solution is added into the round-bottom flask and quickly closed with the two-hole stopper. The 40 cm length of rubber hose is dipped into 1.0 L of water in a graduated cylinder (Figure 2). After equilibrium is established, the pinch-clamp on the 40 cm length of rubber hose is unscrewed. The quantity of water that flows into the roundbottom flask is measured.
As seen from a number of publications, the determination of gas pressure continues to be a favorite subject for an experiment (11, 12). When pressure sensors are provided, the experiment setup shown in Figure 2 allows students to see evidence of a gaseous reagent being consumed. In this experiment, HCl solution instead of water is added to the filter flask to produce more carbon dioxide. As can be seen from the pressure versus time curve shown in Figure 3, the pressure in the round-bottom flask increased when the rubber stopper was inserted and then dramatically decreased to 0.10 atm as it reacts with the sodium hydroxide solution. When the pinch-clamp on the 40 cm length of rubber hose is released, water flows into the round-bottom flask from the graduated cylinder until the pressure inside the round-bottom flask is approximately equal to atmospheric pressure. The round-bottom flask will be almost filled with water. The average value for carbon dioxide consumed is found to be 0.022 mole. Acknowledgments We would like to thank Korea Research Foundation Grant (KRF-2006-721-C00002) for funding this research project and Ed Vitz for the kind correction of this manuscript.
Hazards
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There have been several accidents when flat-bottom flasks such as Erlenmeyer or Florence flasks are used instead of round-bottom flasks to set up the popular ammonia fountain demonstration. Flat-bottom flasks cannot stand the pressure difference produced in this demonstration and often implode causing serious injury to the experimenter (9, 10). NaOH solutions are caustic and should be handled with care.
Photographs of the experimental setup are available in this issue of JCE Online.
Discussion The carbon dioxide fountain exhibits several advantages over the ammonia fountain. It is odorless and makes use of a familiar consumer product, Alka-Seltzer. Ammonia has a pungent smell and students, therefore, are not able to execute the ammonia fountain experiment without a fume hood. No fume hood is necessary for the carbon dioxide fountain. Some caution must be exercised when handling the corrosive NaOH solution. 1672
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Supplemental Material
Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Alexander, M. D. J. Chem. Educ. 1999, 76, 210–211. Proksa, M. J. Chem. Educ. 1995, 72, 931–932. Li, J.; Peng, A.-Z. J. Chem. Educ. 1995, 72, 828–829. Steadman, N. J. Chem. Educ. 1992, 69, 764. Epp, D. N. J. Chem. Educ. 1991, 68, A297. Viswanathan, A.; Gireesan, S. J. Chem. Educ. 1957, 34, A375. Chen, Y. H.; Yaung, J. F. J. Chem. Educ. 2002, 79, 848–850. Sarquis, A. M.; Woodward, L. M. J. Chem. Educ. 1999, 76, 385–387. Kauffman, G. B. J. Chem. Educ. 1982, 59, 80. Weaver, E. C. J. Chem. Educ. 1944, 21, 199. Gordon, J.; Chancey, K. J. Chem. Educ. 2005, 82, 286–287. Branca, M.; Soletta, I. J. Chem. Educ. 2005, 82, 613–615.
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