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Effect of Pressure

Discusses how pressure affects equilibrium direction in systems involving gaseous components.

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See the Bubbles

See the Bubbles

Credit: D. Sharon Pruitt
Source: http://www.flickr.com/photos/40645538@N00/4825113119
License: CC BY-NC 3.0

Have you ever wanted to make your own soft drinks? Maybe you want to save money or maybe you want to experiment with new flavors. Well, now you can do this at home. Carbon dioxide dispensing devices are commercially available that pump CO2 under pressure into water and your flavoring of choice. Root beer, Cola, orange and other flavors can be mixed with the carbonated water for your unique drink. The more creative folks can add ice cream and make a genuine old-fashioned ice cream soda. 

News You Can Use

  • The pH of the average soft drink is strongly acidic, enough so that it could clean the rust off metal. The acidity arises (at least in part) from an equilibrium between dissolved carbon dioxide and hydrogen ions. When CO2 is dissolved in water, we see the formation of hydrogen ions and bicarbonate anions. According to LeChâtelier’s principle, adding more carbon dioxide will increase the H+ concentration and thus lower the pH.
  • When the soft drink container is opened, there is the release of pressure in the container. You can often hear the carbon dioxide escaping as soon as the lid is removed. As the carbon dioxide vents, its concentration in the liquid will decrease. This change causes a shift in the equilibrium, moving it to the left toward more CO2 formation. In order for this to happen, hydrogen cations and bicarbonate anions need to combine to form the carbon dioxide and water. As a result, the hydrogen ion concentration will decrease, causing a rise in the pH.
  • If the drink is heated, more CO2 will be liberated from solution. Leaving a closed can out in the sun and then opening it will usually lead to a large release of gas. If the opened drink is allowed to warm to room temperature, after a while the drink will warm and CO2 will escape. In either case, the increase in temperature will remove carbon dioxide from solution, again shifting the equilibrium to the left. When the drinks are manufactured, the materials are kept at a low temperature to facilitate dissolving of more CO2 .
  • Credit: Kai Chan Vong
    Source: http://www.flickr.com/photos/kaichanvong/12379250844/
    License: CC BY-NC 3.0

    The Sodastream allows you to create your own carbonated drinks [Figure2]

  • Watch a video at the link below to learn how to make soft drinks: https://www.youtube.com/watch?v=PwLimydKBT8

Show What You Know

Use the links below to learn more about carbonation of soft drinks. Then answer the following questions.

  1. What was Priestley’s 1772 method for production of carbonated water?
  2. Is drinking carbonated water a health hazard?
  3. When is carbonation added to the soft drink?
  4. What happens to soft drinks in plastic bottles?

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    Image Attributions

    1. [1]^ Credit: D. Sharon Pruitt; Source: http://www.flickr.com/photos/40645538@N00/4825113119; License: CC BY-NC 3.0
    2. [2]^ Credit: Kai Chan Vong; Source: http://www.flickr.com/photos/kaichanvong/12379250844/; License: CC BY-NC 3.0

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