What Is the Pressure Inside a Bottle of Soda?

What is the pressure in a soda?

Bottles of soda are sealed under high pressures of CO2, or PCO2. This causes a substantial amount of CO2 to dissolve into the beverage, giving the drink its fizziness. But what exactly is the pressure inside a bottle of soda?

A student of mine (Andrea Sturgis) and I worked together for several years to try to answer this question.1,2 To do this we slightly modified a published method3 for finding the pressure in soda bottles. The analysis involves a simple application of the ideal gas law. You can watch a description of what we did below:

Video 1: Measuring the Pressure Inside a Soda Bottle4

This protocol is simple enough that you can carry it out at home if you have an appropriate balance.5 Even though the procedure it simple, it allows for a wide variety of explorations. For example, we determined PCO2 inside bottles of various sizes: 2L, 500 mL, and 355 mL. We found that sodas generally contain pressures between 2.7 and 4.7 bar, as long as the bottles are measured prior to the expiration date stamped on the bottle.  

We further observed that bottles display higher PCO2 at higher temperature (Figure 1). This result can be explained by noting that the escape of CO2(aq) from solution is endothermic:

CO2(aq) + energyCO2(g)              Equation 1

Increasing the temperature of a soda bottle shifts the above equilibrium to the right, causing CO2(aq) in the beverage to escape into the headspace of the bottle. This naturally has the effect of increasing the pressure. What a simple connection to Le Châtelier’s Principle!

Figure 1: PCO2 measured in 500 mL bottles of Diet Pepsi kept at different temperatures.2

 

We also noticed that beverage bottles lost PCO2 over time – even if the bottles remained sealed! Interestingly, the loss of PCO2 from sealed bottles was accelerated by temperature. To show this we stored 355 mL bottles of Diet Coke from the same 8-pack under different conditions of temperature: three bottles next to a heating vent, two at room temperature, and three in the refrigerator.2 After two months of storage the bottles were all brought to room temperature and the PCO2 was tested in each bottle (Figure 2). Average PCO2 values of 3.35 bar, 3.72 bar, and 4.03 bar were measured in the bottles stored next to the heating vent, at room temperature, and in the refrigerator, respectively. This result can be explained using principles of chemical kinetics. Physical and chemical processes occur faster at higher temperature, so CO2 escapes sealed bottles more quickly at higher temperature. We also were able to measure substantial pressure drops in 355 mL bottles of Diet Coke that were stored for two years at room temperature (PCO2 = 0.4 bar) or in the refrigerator (PCO2 = 1.1 bar).1,2 But you don’t need to wait two months or two years to observe this. The loss of CO2 from bottles can be measured by taking mass measurements of sealed bottles daily. Noticeable losses in mass can be detected in just a few days.1,6  

 

Figure 2: PCO2 measured in 355 mL bottles of Diet Coke stored at different temperatures for two months. All pressures were measured after bringing the bottles to room temperature.3

 

The experiments reported here are just a sampling of the work that Andrea and I completed. I also have a few more ideas I have in mind to investigate in the future as well. Hopefully this short report will give you some inspiration to try out this experiment, and perhaps even carry out some explorations of your own. As always, I look forward to hearing from you if you learn anything interesting.

Happy experimenting!

Notes and References:

1. Kuntzleman, T.S.; Sturgis, A. The Effect of Temperature in Experiments Involving Carbonated Beverages. J. Chem. Educ. 2020, 97 (11), 4033-4038.

2. Sturgis, A. The Effect of Temperature in Experiments Using Commercially Carbonated Beverages. Undergraduate Thesis, Spring Arbor University, Spring Arbor, MI, 2018.

3. de Grys, H. Determining the Pressure inside an Unopened Carbonated Beverage. J. Chem. Educ. 2007, 84 (7), 1117-1119.

4. Tommy Technetium, Measuring the Pressure Inside a Soda Bottle, . Accessed December 2020.

5. A balance with a capacity of at least 500 g and precision of at least 0.01 g is recommended. At the time of this writing, balances with these specifications can be purchased on Amazon for $15-$40.

6. About 20 mg from 355 mL bottles of Diet Coke per day at room temperature – about 2 mg per day for bottles stored in the refrigerator.

NGSS

Analyzing data in 9–12 builds on K–8 and progresses to introducing more detailed statistical analysis, the comparison of data sets for consistency, and the use of models to generate and analyze data.

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Analyzing data in 9–12 builds on K–8 and progresses to introducing more detailed statistical analysis, the comparison of data sets for consistency, and the use of models to generate and analyze data. Analyze data using tools, technologies, and/or models (e.g., computational, mathematical) in order to make valid and reliable scientific claims or determine an optimal design solution.

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Asking questions and defining problems in grades 9–12 builds from grades K–8 experiences and progresses to formulating, refining, and evaluating empirically testable questions and design problems using models and simulations.

Summary:

Asking questions and defining problems in grades 9–12 builds from grades K–8 experiences and progresses to formulating, refining, and evaluating empirically testable questions and design problems using models and simulations.

questions that challenge the premise(s) of an argument, the interpretation of a data set, or the suitability of a design.

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Scientific questions arise in a variety of ways. They can be driven by curiosity about the world (e.g., Why is the sky blue?). They can be inspired by a model’s or theory’s predictions or by attempts to extend or refine a model or theory (e.g., How does the particle model of matter explain the incompressibility of liquids?). Or they can result from the need to provide better solutions to a problem. For example, the question of why it is impossible to siphon water above a height of 32 feet led Evangelista Torricelli (17th-century inventor of the barometer) to his discoveries about the atmosphere and the identification of a vacuum.

Questions are also important in engineering. Engineers must be able to ask probing questions in order to define an engineering problem. For example, they may ask: What is the need or desire that underlies the problem? What are the criteria (specifications) for a successful solution? What are the constraints? Other questions arise when generating possible solutions: Will this solution meet the design criteria? Can two or more ideas be combined to produce a better solution?

Constructing explanations and designing solutions in 9–12 builds on K–8 experiences and progresses to explanations and designs that are supported by multiple and independent student-generated sources of evidence consistent with scientific ideas, principles, and theories.

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Constructing explanations and designing solutions in 9–12 builds on K–8 experiences and progresses to explanations and designs that are supported by multiple and independent student-generated sources of evidence consistent with scientific ideas, principles, and theories. Construct and revise an explanation based on valid and reliable evidence obtained from a variety of sources (including students’ own investigations, models, theories, simulations, peer review) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future.

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Modeling in 9–12 builds on K–8 and progresses to using, synthesizing, and developing models to predict and show relationships among variables between systems and their components in the natural and designed worlds.

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Modeling in 9–12 builds on K–8 and progresses to using, synthesizing, and developing models to predict and show relationships among variables between systems and their components in the natural and designed worlds. Use a model to predict the relationships between systems or between components of a system.

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Constructing explanations and designing solutions in 9–12 builds on K–8 experiences and progresses to explanations and designs that are supported by multiple and independent student-generated sources of evidence consistent with scientific ideas, principles, and theories.

Summary:

Constructing explanations and designing solutions in 9–12 builds on K–8 experiences and progresses to explanations and designs that are supported by multiple and independent student-generated sources of evidence consistent with scientific ideas, principles, and theories. Construct and revise an explanation based on valid and reliable evidence obtained from a variety of sources (including students’ own investigations, models, theories, simulations, peer review) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future.

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Engaging in argument from evidence in 9–12 builds on K–8 experiences and progresses to using appropriate and sufficient evidence and scientific reasoning to defend and critique claims and explanations about natural and designed worlds. Arguments may also come from current scientific or historical episodes in science.

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Engaging in argument from evidence in 9–12 builds on K–8 experiences and progresses to using appropriate and sufficient evidence and scientific reasoning to defend and critique claims and explanations about natural and designed worlds. Arguments may also come from current scientific or historical episodes in science.
Evaluate the claims, evidence, and reasoning behind currently accepted explanations or solutions to determine the merits of arguments.

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Mathematical and computational thinking at the 9–12 level builds on K–8 and progresses to using algebraic thinking and analysis, a range of linear and nonlinear functions including trigonometric functions, exponentials and logarithms, and computational tools for statistical analysis to analyze, represent, and model data. Simple computational simulations are created and used based on mathematical models of basic assumptions. Use mathematical representations of phenomena to support claims.

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Students who demonstrate understanding can apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.

*More information about all DCI for HS-PS1 can be found at  and further resources at .

 

Summary:

Students who demonstrate understanding can apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.

Assessment Boundary:

Assessment is limited to simple reactions in which there are only two reactants; evidence from temperature, concentration, and rate data; and qualitative relationships between rate and temperature.

Clarification:

Emphasis is on student reasoning that focuses on the number and energy of collisions between molecules.

Students who demonstrate understanding can refine the design of a chemical system by specifying a change in conditions that would produce increased amounts of products at equilibrium.

*More information about all DCI for HS-PS1 can be found at  and further resources at .

Summary:

Students who demonstrate understanding can refine the design of a chemical system by specifying a change in conditions that would produce increased amounts of products at equilibrium.

Assessment Boundary:

Assessment is limited to specifying the change in only one variable at a time. Assessment does not include calculating equilibrium constants and concentrations.

Clarification:

Emphasis is on the application of Le Chatelier’s Principle and on refining designs of chemical reaction systems, including descriptions of the connection between changes made at the macroscopic level and what happens at the molecular level. Examples of designs could include different ways to increase product formation including adding reactants or removing products.

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Comments 10

Chad Husting's picture
Chad Husting | Thu, 12/31/2020 - 07:31

Food for thought....this would make a great virtual exam question.  Thanks for great work!

Tom Kuntzleman's picture
Tom Kuntzleman | Fri, 01/01/2021 - 09:46

Thanks, Chad. I used this as a virtual lab in a science course for non-majors. You can check out how that was done at the video linked . A couple of things about the video. First, the gas constant you see being used in the ideal gas law is kind of goofy (R = 1.87 mL atm-1 g-1 CO2 K-1). It was a non-majors course, and I didn't teach them about moles. Thus the gas constant was listed in terms of grams of CO2 and not moles. I also used mL rather than L in the gas constant to help students with conversions. Second... be careful to notice that two of the temperature measurements need to be converted from Fahrenheit to Kelvin!

Nice pun, by the way.

Pierre-Jean LHeureux | Sun, 01/03/2021 - 17:15

Thank you so much for this bright idea. It's simple enough for students to understand the measurements, but versatile enough to engage many fundamental concepts. 

Tom Kuntzleman's picture
Tom Kuntzleman | Mon, 01/04/2021 - 08:43

Thank you for commenting, Pierre-Jean. Please do let us know if you find any other concepts that connect to this experiment.

Laura Mashburn | Thu, 01/07/2021 - 13:38

This is actually a good experiment, temperature does effect the amount of pressure that is built up inside the bottle a lot more than we actually realize in our day to day life.

Tom Kuntzleman's picture
Tom Kuntzleman | Fri, 01/08/2021 - 15:46

Thank you for the comment Laura! You know, I wonder what would happen if you FROZE the soda?! Hmmmm....maybe you and your students could explore this...

Izzy Frederick | Thu, 01/07/2021 - 20:07

This would be interesting to test between Coke and Dr. Pepper. We all know how fizzy and explosive Dr. Pepper gets. Would this also work on sparkling water and club sodas? 

Tom Kuntzleman's picture
Tom Kuntzleman | Fri, 01/08/2021 - 15:51

Andrea and I tested several sodas, but all were various versions of Coke and Pepsi (Diet Coke, caffeine free Coke, regular Pepsi, and so on). However, we did NOT try any versions of Dr. Pepper. Please do let me know your results if you experiment with Dr. Pepper! I have tested club soda and sparkling water with this method, but I haven't conducted an in-depth analysis. I will caution you that club soda and sparkling water tends to degas quite easily, so when testing these it will be important to pay close attention to the quick "open and close" method of letting the gas escape.

AnnaMarie Bair's picture
AnnaMarie Bair | Sat, 01/09/2021 - 11:28

Thank you!   I will definitely steal your video for this year but create a lab around this next year!   Love the students using so many previous learned skills to put this together.   I also will add a conclusion regarding the results of the data .... since in solubility we explore oxygen levels verses fish life .... gases dissolve better in colder temperatures   vs.   solids in warmer temperatures.

Tom Kuntzleman's picture
Tom Kuntzleman | Sun, 01/10/2021 - 19:58

Hi AnnaMarie. Please do drop me another line to let me know what you learn when you and your students conduct these experiments. Thank you for commenting!