Chemical Equilibrium with Soda Water

Measuring the change in pressure inside a container as a small amount of soda water (seltzer) decomposes.

Lab Summary

Students will use an Absolute Pressure Sensor to measure the change in pressure inside a container as a small amount of soda water (seltzer) decomposes. Students will determine whether the temperature of soda water affects the rate at which equilibrium is established.\

Students will use an Absolute Pressure Sensor to measure the change in pressure inside a container as a small amount of soda water (seltzer) decomposes. Students will determine whether the temperature of soda water affects the rate at which equilibrium is established.

All carbonated soft drinks contain small amounts of carbonic acid. Carbonic acid decomposes to form carbon dioxide and water in the following equilibrium system:

   H₂CO₃(aq)      <=======>               CO₂(g)           +     H₂O(aq)
Carbonic Acid                           Carbon Dioxide            Water

The carbon dioxide then reacts with water to re-form carbonic acid. The forward reaction occurs every time you open a soda bottle or pour soda into a glass. The carbonic acid decomposes to form carbon dioxide, producing the "fizz" that we associate with most soft drinks.

When you cap the bottle, the carbon dioxide gas begins to re-dissolve in the soda water to reform carbonic acid. Once the rate of the forward decomposition equals the rate of re-formation of carbonic acid, the system has reached chemical and physical equilibrium. The reactions still occur at the microscopic level but there is no evidence of any macroscopic change. You will know when the carbonic acid/carbon dioxide system has reached equilibrium when there is no further change in the pressure in the soda bottle.

Published: March 2002

Downloads

• Chemical Equilibrium with Soda Water - PASPORT (48 KB, .zip)

  Includes experiment setup, procedures and Datastudio file

• Chemical Equilibrium with Soda Water - ScienceWorkshop (48 KB, .zip)

  Includes experiment setup, procedures and Datastudio file

Here's What You Need

U.S. Educator prices shown.

Probeware (PASPORT Systems)

Xplorer GLX (PS-2002) - $349

The Xplorer GLX is a data collection, graphing, and analysis tool designed for science students and educators.

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PASPORT Absolute Pressure Sensor (PS-2107) - $90

Measures gas pressure from various sources and internal vacuum allows consistent measurement above and below ambient conditions. For use with PASPORT Interfaces.

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Probeware (ScienceWorkshop Systems)

750 Interface, USB (CI-7650) - $679

The 750 Interface allows students to measure force, temperature, pressure, angular velocity, acceleration, current, and magnetic field with a built-in function generator and oscilloscope mode.

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Pressure Sensor (Absolute) (CI-6532A) - $125

Measures the gas pressure in a closed or open system (containeror atmospheric pressure).

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Other Materials

• Soda Water (cold)
• Soda Water (warm or room temp)
• 250 mL Flask
• 100 mL graduated cylinder
• Rubber stopper (single hole)
• Goggles