In the Classroom
JCE DigiDemos: Tested Demonstrations Ed Vitz
Kutztown, PA 19530
Carbon Dioxide Fountain W
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@example.com
checked by: Mark Case
Emmaus High School, 500 Macungie Ave, Emmaus, PA 18049
Demonstrations are interesting. They grab students’ at- ter and two Alka-Seltzer tablets are added to the filter flask
tention and can provide concrete examples of abstract con- and the flask is closed with a solid rubber stopper. A one-
cepts. The ammonia fountain is a classic demonstration that hole rubber stopper is prepared for the 500 mL round-bot-
has been a popular experiment for decades. This experiment tom flask. A glass tube, which goes almost to the bottom of
is pertinent to the students’ understanding of solubility of the flask, is inserted in to the stopper and is attached to a 30
gases, acid–base interactions, matter flow by pressure differ- cm length of rubber hose. The round-bottom flask is filled
ence, and other concepts (1–6). An HCl fountain is also a with the generated carbon dioxide and then 30 mL of 2.0 M
known demonstration, but no description of a carbon diox- NaOH solution is added to the round-bottom flask. The
ide fountain has been published. In connection with our on- round-bottom flask is quickly closed with the one-hole rub-
going effort to develop chemical demonstrations, we have ber stopper and a pinch-clamp is used on the rubber hose to
developed the carbon dioxide fountain using consumer prevent carbon dioxide from escaping. The round-bottom
chemicals. flask is carefully inverted and clamped to a ring stand. A 500
Alka-Seltzer is often taken for acid indigestion. The ac- mL beaker containing 400 mL of water and small quantity
tive ingredients in Alka-Seltzer are sodium bicarbonate, cit- of bromothymol blue indicator is placed below the round-
ric acid, and aspirin. When an Alka-Seltzer tablet is dissolved bottom flask and the rubber hose from the flask is submerged
in water, sodium bicarbonate reacts with acid to generate car- under the water surface in the beaker (Figure 1). After sev-
bon dioxide gas (7, 8): eral minutes, the pinch-clamp on the rubber hose is un-
screwed. The fountain is observed immediately.
3NaHCO3(aq) + H3C6H5O7(aq)
citric acid Measurement of the Pressure Decline
Using a Gas Pressure Sensor
3CO2(g) + 3H2O + Na3C6H5O7(aq)
A 40 cm length of rubber hose is attached to the outlet
NaHCO3(aq) + HC 9H7 O4(aq) of a 250 mL filter flask and the other end is placed in a 500
aspirin mL round-bottom flask. Water, 10 mL, and bromothymol
blue indicator are added to the round-bottom flask. Then
CO2(g) + H2O + NaC 9H7 O4(aq) about 50 mL of 1.0 M HCl solution and five Alka-Seltzer
These reactions are used as a carbon dioxide gas source in tablets are added to the filter flask and the flask is closed with
the demonstration of the carbon dioxide fountain. a solid rubber stopper. A two-hole rubber stopper for the 500
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) 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 solu-
tion reducing its pressure, water is driven by atmospheric pres-
sure up from the beaker through the glass tube creating the
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 wa- Figure 1. Schematic of the carbon dioxide fountain.
www.JCE.DivCHED.org • Vol. 84 No. 10 October 2007 • Journal of Chemical Education 1671
In the Classroom
Figure 3. A pressure versus time curve for the reaction between
carbon dioxide and NaOH solution.
As seen from a number of publications, the determina-
tion 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 ex-
Figure 2. Schematic of the carbon dioxide fountain using a pres- periment, HCl solution instead of water is added to the fil-
sure sensor. ter 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
mL round-bottom flask is prepared: in one hole a glass tube when the rubber stopper was inserted and then dramatically
that goes half way to the bottom of the flask is inserted and decreased to 0.10 atm as it reacts with the sodium hydroxide
in the second hole a glass tube that reaches just below the solution. When the pinch-clamp on the 40 cm length of rub-
stopper is inserted. A 15 cm length of rubber hose is attached ber hose is released, water flows into the round-bottom flask
to the short glass tube and a 40 cm length is attached to the from the graduated cylinder until the pressure inside the
long glass tube. The 40 cm length of rubber hose is closed round-bottom flask is approximately equal to atmospheric
with a pinch-clamp and the 15 cm length of rubber hose is pressure. The round-bottom flask will be almost filled with
connected to a pressure sensor. The round-bottom flask is water. The average value for carbon dioxide consumed is
filled with the generated carbon dioxide and then 50 mL of found to be 0.022 mole.
2.0 M NaOH solution is added into the round-bottom flask
and quickly closed with the two-hole stopper. The 40 cm Acknowledgments
length of rubber hose is dipped into 1.0 L of water in a gradu-
ated cylinder (Figure 2). After equilibrium is established, the We would like to thank Korea Research Foundation
pinch-clamp on the 40 cm length of rubber hose is un- Grant (KRF-2006-721-C00002) for funding this research
screwed. The quantity of water that flows into the round- project and Ed Vitz for the kind correction of this manu-
bottom flask is measured. script.
There have been several accidents when flat-bottom Photographs of the experimental setup are available in
flasks such as Erlenmeyer or Florence flasks are used instead this issue of JCE Online.
of round-bottom flasks to set up the popular ammonia foun-
tain demonstration. Flat-bottom flasks cannot stand the pres- Literature Cited
sure difference produced in this demonstration and often
implode causing serious injury to the experimenter (9, 10). 1. Alexander, M. D. J. Chem. Educ. 1999, 76, 210–211.
NaOH solutions are caustic and should be handled with care. 2. Proksa, M. J. Chem. Educ. 1995, 72, 931–932.
3. Li, J.; Peng, A.-Z. J. Chem. Educ. 1995, 72, 828–829.
Discussion 4. Steadman, N. J. Chem. Educ. 1992, 69, 764.
5. Epp, D. N. J. Chem. Educ. 1991, 68, A297.
The carbon dioxide fountain exhibits several advantages 6. Viswanathan, A.; Gireesan, S. J. Chem. Educ. 1957, 34, A375.
over the ammonia fountain. It is odorless and makes use of a 7. Chen, Y. H.; Yaung, J. F. J. Chem. Educ. 2002, 79, 848–850.
familiar consumer product, Alka-Seltzer. Ammonia has a pun- 8. Sarquis, A. M.; Woodward, L. M. J. Chem. Educ. 1999, 76,
gent smell and students, therefore, are not able to execute 385–387.
the ammonia fountain experiment without a fume hood. No 9. Kauffman, G. B. J. Chem. Educ. 1982, 59, 80.
fume hood is necessary for the carbon dioxide fountain. Some 10. Weaver, E. C. J. Chem. Educ. 1944, 21, 199.
caution must be exercised when handling the corrosive 11. Gordon, J.; Chancey, K. J. Chem. Educ. 2005, 82, 286–287.
NaOH solution. 12. Branca, M.; Soletta, I. J. Chem. Educ. 2005, 82, 613–615.
1672 Journal of Chemical Education • Vol. 84 No. 10 October 2007 • www.JCE.DivCHED.org