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Opening can of pop

 

A person opens a can of pop (explosivekeeper, iStockphoto)

 

STEM in Context

The Chemistry of Pop

Patrick Clarke & Let's Talk Science
Format
Video Text Images
Grade
9 10 11 12
Jurisdiction
AB BC MB NB NL NS NT NU ON PE QC SK YT
Readability
6.86
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Summary

There’s a lot of cool chemistry in a can of pop! Learn how solubility, chemical equilibrium, acids & bases and gas laws work in some of your favourite drinks.

When you first open a can of Coca-Cola, what’s the first thing you notice? Maybe it’s that fizzing sound. Maybe it’s the sight or sound of bubbles rising and popping. But did you know that fizz is actually a chemical process? In fact, inside every can or bottle of pop, there is some pretty cool chemistry going on.

Did you know?

Coca-Cola is the world’s best-selling pop. It was invented in 1886 by a pharmacist who originally wanted to sell it as a medicine. Back then, Coca-Cola cost five cents a glass!

Why is pop fizzy?

Many people love the feeling of bubbles bursting in their mouths when they drink pop. These bubbles happen because of carbonation. Carbonation occurs when carbon dioxide (CO2) dissolves in water (H2O) or an aqueous (watery) solution.

Carbon dioxide doesn’t easily dissolve in water under everyday conditions. To make this happen, manufacturers need to increase the pressure in the can (or bottle) and keep it at a low temperature. Under these conditions, water molecules can trap lots of CO2 molecules.

The can is then sealed so that it is airtight. This way, the inside of the can maintains enough pressure to prevent the extra CO2 molecules from escaping. Inside the can, CO2 exists in two forms. Some CO2 dissolves in water. Some CO2 sits in gas form between the top of the bottle or can and the liquid.

What chemical reactions are going on inside a pop can?

When CO2 dissolves in H2O, water and gaseous carbon dioxide react to form a dilute solution of carbonic acid (H2CO3).

The chemical reaction for this process is: H2O + CO2 ⇋ H2CO3  

Note that the reactants, H2O and CO2 , are on the left. The product,  H2CO3 , is on the right.

Notice the symbol ⇋ in the chemical equation. This symbol shows that the reaction is reversible. That means it can go forwards and backwards. The carbonic acid can be converted back to water and carbon dioxide. When a can of pop is sealed, high pressure inside the can forces the chemical reaction to the right (the forward reaction).

Forward reaction of carbonic acid
Forward reaction of water and carbon dioxide to form carbonic acid.

In other words, carbonic acid is produced. The forward reaction continues until concentration of the reactants and products no longer changes. In other words, when the two chemical reactions are in equilibrium.

But once you open that can, the pressure is released. This shifts the chemical reaction to the left (the backward reaction).

Backward reaction of carbonic acid
Backward reaction of carbonic acid to form water and carbon dioxide.

Remember that gaseous CO2 at the top of the can? Once you open the can, it escapes. And now that the can is no longer under pressure, the dissolved CO2 starts coming out of the solution. This forms bubbles, which release the CO2 into the air.

The escaping CO2 lowers the concentration of CO2 in the pop. Because of this lower concentration, the carbonic acid turns back to CO2 and H20. The result is a new equilibrium.

This video takes a closer look at carbonated beverages, from seltzer to sparkling wine, to find out what makes them bubbly—and what makes them go flat (4:31 min)

 

Why does fizz taste so good?

Have you ever noticed that fizzy pop tastes better than flat pop? That has nothing to do with the bubbles. It’s actually because in a fizzy drink, the dilute carbonic acid creates a slight burning sensation on your tongue.

This doesn’t happen when pop goes flat. When pop is left out in the open, CO2 continually escapes. Let’s look at that chemical equation again.

H2O + CO2 ⇋ H2CO

As CO2 bubbles away from the liquid, the reactants and products move again towards equilibrium. This causes the backward reaction to take over. As that happens, the concentration of carbonic acid in the drink gets lower and lower. As the amount of H2CO3 in the beverage goes down, so does the soda’s ability to bring about that tingling sensation on your tongue.

Did you Know?  

The carbonation process was invented by a famous English chemist named Joseph Priestley in 1767.  A few years later, a Swiss scientist named Jacob Schweppe created the world’s first soft drink: Schweppe’s Tonic Water! 

Why do people like drinking pop?

Why do some people enjoy the tingling sensation of carbonated drinks in the first place? Scientists are not entirely sure. In fact, studies have found that many other mammals actually avoid drinking carbonated liquids. Some scientists believe that humans like fizzy drinks because we like a bit of risk in our lives. It’s like why some people really enjoy spicy food. And let’s not forget that other reason why people might like fizzy drinks: they contain a lot of sugar!

 

This video from DNews explains why we like bubbly beverages (3:37 min.)

What have you learned about pop?

Let’s recap.

  • Pop contains carbonic acid, which forms when CO2 is dissolved in water.
  • In every can (or bottle) of pop, carbonic acid and gaseous CO2  exist in chemical equilibrium.
  • When you open a can of pop, gaseous CO2 escapes. You see bubbles and hear the sound of fizz. The chemical equilibrium between the carbonic acid and the CO2  shifts. 
  • When pop goes flat, that’s the concentration of carbonic acid in the drink getting lower.
  • Many animals really dislike pop.
  • And finally: if you love pop, you may be a bit of a risk-taker! 
This video from History Channel looks at how CO2 gets into water to form the base of carbonated beverages (1:49 min.)

Starting Points

Connecting and Relating
  • What is your favorite pop and why?
  • Would you drink a non-carbonated or “flat” pop? Why/why not?
  • Do you have a soda-making machine at home, or have you ever used one? How successful is it at making drinks fizz?
  • Have you ever played any silly tricks with a can of pop? What did you do and what happened? 
     
Connecting and Relating
  • What is your favorite pop and why?
  • Would you drink a non-carbonated or “flat” pop? Why/why not?
  • Do you have a soda-making machine at home, or have you ever used one? How successful is it at making drinks fizz?
  • Have you ever played any silly tricks with a can of pop? What did you do and what happened? 
     
Relating Science and Technology to Society and the Environment
  • Should governments fund chemical research that aims to make food tastier, last longer, and more attractive to people? Why/why not?
  • At-home carbonation machines are becoming increasingly popular. Why do you think this is happening? 
  • How does an idea such as “carbonated water is good for your health” become widespread and accepted in society? Explain.
     
Relating Science and Technology to Society and the Environment
  • Should governments fund chemical research that aims to make food tastier, last longer, and more attractive to people? Why/why not?
  • At-home carbonation machines are becoming increasingly popular. Why do you think this is happening? 
  • How does an idea such as “carbonated water is good for your health” become widespread and accepted in society? Explain.
     
Exploring Concepts
  • Describe the process of equilibrium in a chemical reaction.
  • Explain how pressure and solubility affect the fizz and lack of fizz in carbonated beverages.
  • Research the health effects of consuming pop on a regular basis.
     
Exploring Concepts
  • Describe the process of equilibrium in a chemical reaction.
  • Explain how pressure and solubility affect the fizz and lack of fizz in carbonated beverages.
  • Research the health effects of consuming pop on a regular basis.
     
Nature of Science/Nature of Technology
  • Is the study of food chemistry “real” science? Explain.
     
Nature of Science/Nature of Technology
  • Is the study of food chemistry “real” science? Explain.
     
Media Literacy
  • What are some ways the media influences individuals to buy soft drinks and other non-essential food products?
  • Create your own commercial, advertisement, or job ad related to a career in chemistry and/or food sciences.
  • Should the media play a role in informing the public of potential negative impacts of our food choices? Explain.
     
Media Literacy
  • What are some ways the media influences individuals to buy soft drinks and other non-essential food products?
  • Create your own commercial, advertisement, or job ad related to a career in chemistry and/or food sciences.
  • Should the media play a role in informing the public of potential negative impacts of our food choices? Explain.
     
Teaching Suggestions
  • This article and the embedded videos support teaching and learning related to acids and bases, chemical equilibrium, solubility and gas laws in chemistry. The article introduces the concepts of carbonation and reversible reactions.
  • Before reading the article, the teacher could get students thinking about carbonation in general by asking questions from the Connecting and Relating section. 
  • After reading the article and viewing the embedded videos, students could complete a Key Ideas Round Robin learning strategy to summarize the key points presented. Download ready-to-use reproducibles using the Key Ideas Round Robin strategy for this article in [Google doc] and [PDF] formats.
  • Students could also use a Print-Video Venn Diagram Learning Strategy to compile and compare information from the video Science: Love Seltzer, Champagne, or Soda? We Explain Carbonation & Bubbles in Fizzy Beverages  and this article. Downloadable ready-to-use Print-Video Venn diagrams are available in [Google doc] and [PDF] formats. 
  • To include hands-on science inquiry connected with carbonation, students could: 
    • Compare different brands/types of pop to see how long it takes each type to go completely flat (no fizz at all). 
    • Explore carbonating different types of liquids (e.g., orange juice, lemonade, ice tea, milk) using a do-it-yourself carbonation machine to see what happens and how successful they are at creating fizzy drinks.
       
Teaching Suggestions
  • This article and the embedded videos support teaching and learning related to acids and bases, chemical equilibrium, solubility and gas laws in chemistry. The article introduces the concepts of carbonation and reversible reactions.
  • Before reading the article, the teacher could get students thinking about carbonation in general by asking questions from the Connecting and Relating section. 
  • After reading the article and viewing the embedded videos, students could complete a Key Ideas Round Robin learning strategy to summarize the key points presented. Download ready-to-use reproducibles using the Key Ideas Round Robin strategy for this article in [Google doc] and [PDF] formats.
  • Students could also use a Print-Video Venn Diagram Learning Strategy to compile and compare information from the video Science: Love Seltzer, Champagne, or Soda? We Explain Carbonation & Bubbles in Fizzy Beverages  and this article. Downloadable ready-to-use Print-Video Venn diagrams are available in [Google doc] and [PDF] formats. 
  • To include hands-on science inquiry connected with carbonation, students could: 
    • Compare different brands/types of pop to see how long it takes each type to go completely flat (no fizz at all). 
    • Explore carbonating different types of liquids (e.g., orange juice, lemonade, ice tea, milk) using a do-it-yourself carbonation machine to see what happens and how successful they are at creating fizzy drinks.
       

Learn more

The compressed chemistry of carbonation  (2015)

CNet Appliance Science - More details about its history, what happens when carbonated beverages are heated or cooled, and why Mentos and Coke shouldn’t mix!

The Secret Science of Soda

An animated introduction to the subject from the American Chemical Association aimed at younger children, including a printable PDF.

Make your own pop recipe

Complete instructions from Science Buddies on how to make your own fizzy drinks with scientific background information.

References

Crandall, P. , Chen, C. S., Nagy, S. , Perras, G. , Buchel, J. A., & Riha, W. (2000). Beverages, nonalcoholic. Ullmann's Encyclopedia of Industrial Chemistry, 5, 418-457. DOI: 10.1002/14356007.a04_035
 

Paul Daubenmire. (n.d.). 13.4: Solutions of gases in water: How soda pop gets its fizz. LibreTexts.

Patrick Clarke

Patrick Clarke is a first year student of the University of Toronto at Scarborough. He is doing a specialist in Journalism and a major in English. Patrick wishes to pursue a career in Broadcast Journalism. His brother, who is two years his senior, also attends UTSC, and because they look so much alike, Patrick's friends often mistake him for his brother, and vice versa.