A COMPARISON OF THE SOLUBILITIES OF CARBON DIOXIDE IN WATER AT VARIOUS TEMPERATURES
By making measurements on a sample of
carbon dioxide, students are able to determine the molar volume of CO2. They arealso introduced to the concept of buoyancy and its importance when massing objects whose masses are small compared to their volumes.
This experiment is appropriate
for a general or first-year college-prep course. Using Seltzer
water samples at various temperatures, students determine how
the solubility of carbon dioxide in water varies with temperature.
The-acid, formed when carbon dioxide reacts with water, is titrated
with sodium hydroxide solution to a phenolphthalein endpoint.
One lab period.
*See Modifications / Substitutions.
The NaOH solution is caustic; avoid
contact with skin. Goggles must be worn throughout the experiment.
- Seltzer water
- 2.0 M NaOH solution (80 g NaOH dissolved in enough distilled or deionized water to make 1.0 liter of solution)*
- phenolphthalein solution (1% in ethanol)*
- 1-L beakers*
- ice bath and warm water bath - large enough to hold a 1-L beaker
- 100-mL graduated cylinders
- 200-mL Erlenmeyer flasks
- eye dropper or Pasteur pipet*
Sample preparation by teacher
- Sodium hydroxide is available as lye in grocery stores.
- Phenolphthalein indicator may be prepared by dissolving crushed
Ex-Lax tablets from a drugstore in ethanol and filtering. Ethanol
is available as rubbing alcohol, but isopropyl alcohol is also
sold as rubbing alcohol.
- Any large jar or other container could be substituted for
the 1-L beakers.
Experimental procedure for students
- Prior to lab session, prepare samples by placing unopened
bottles of Seltzer water in an ice-water bath until samples are
at temperature of bath.
- About 0.5 hour before students are to begin experiment, open
the necessary number of bottles of Seltzer water. Mix the contents,
divide into three 1-L beakers, and replace one beaker in the ice-water
bath. Allow one beaker of Seltzer to stand at room temperature
and place the other in a warm water bath.
Titrated samples may be disposed
of by flushing down the drain with running water.
Carbonated beverages are bottled
under a carbon dioxide pressure slightly greater than 1 atmosphere.
When the bottles are opened to the air, the partial pressure of
CO2 above the solution is decreased and CO2 bubbles out of the
solution. The bottles should be cold when opened because CO2 is
most soluble at low temperatures. Bottles should be opened prior
to doing the experiment to allow the dissolved CO2 to reach equilibrium
with the lower pressure of CO2 in the air. Preparing the samples
early also allows each sample to reach temperature equilibrium.
When carbon dioxide dissolves in water it reacts with water to
form an acidic solution which can be neutralized by the addition
- Measure out 50 mL of Seltzer water and transfer to an Erlenmeyer
flask. Add 3 drops phenolphthalein solution and swirl gently for
one minute to remove any remaining mechanically trapped carbon
- Using a dropper, titrate with 2.0 M NaOH solution until
the pink phenolphthalein color persists for 30 seconds. Record
the number of drops of NaOH solution used.
- Repeat steps 1 and 2 using samples at different temperatures.
- Multiple samples may be titrated if time permits.
- Plot a graph of drops of NaOH solution required for neutralization
vs. temperature and draw conclusion about how the solubility of
carbon dioxide varies with temperature.
CO2 (aq) + H2O (l) <====> H+(aq) + HCO3-(aq) [sometimes
written as H2CO3 (aq)]
Results obtained by this procedure are intended
to indicate a trend in the solubility of the carbon dioxide as
a function of temperature. They will not agree with literature
values for the solubility of carbon dioxide which are usually
measured at higher partial pressures of the gas.
Brown, T.L. and LeMay, H.E., Jr., Chemistry - The Central
Science, Prentice-Hall, Inc., Englewood Cliffs, NJ, 1981.
Chaps. 12, 15, and 17 discuss the chemistry of solutions of carbon
dioxide in water.
the procedure is rather straight forward, it is necessary to be
careful to provide samples that vary only in their temperature
and that students use reproducible methods in doing the experiment.
Best results are obtained when the dropper is held vertically
- The pre-lab preparation should include discussion
of how students can standardize their methods and may include
some discussion of how the samples are prepared to eliminate variables.
Gordon, G. and Keifer, The Delicate
Balance, Harper & Row, Publishers, New York, 1980, pp.
110-111. In an experiment described here, bottles of Seltzer water
maintained at three temperatures are opened and the acid (from
dissolved CO2) is titrated using burets.
Submitted by Eva Lou Apel, Michael Bannon, Joseph Baron, John Brodemus, and Elna Clevenger
Woodrow Wilson Leadership Program in Chemistry
The Woodrow Wilson National Fellowship Foundation
CN 5281, Princeton NJ 08543-5281