Ask A Scientist
What are the bubbles in soda?
Asked by: Kaida Warwick
School: Chenango Bridge Elementary School
Teacher: Mrs. Shafer
Hobbies/Interests: Dancing, reading, math, softball
Career Interest: The sky is the limit
Answer from Wayne Jones
Professor and Chair
Water is the main ingredient in soda. The bubbles in soda are the result of gas that is dissolved in the water. Just like salt will dissolve in water, gasses can also dissolve in water. For example, fish actually breathe oxygen that has been dissolved in water.
When you open a can or bottle of soda, you can hear gas escaping in the form of a hissing sound. This is because the liquid in the can has been packaged under high pressure with carbon dioxide (CO2) gas. The total pressure of the CO2 gas is very high, up to 1,200 pounds per square inch. Gasses dissolve in liquids better under high-pressure conditions. They also dissolve better at low temperatures. When you open the can or bottle, all that pressure is released forming the bubbles. The same thing happens as you warm soda up. Have you ever noticed that when you don’t put the cap on the bottle it goes "flat"? That is because all of the dissolved CO2 has been released. This happens even faster if you let the bottle warm up or if you open the can where there is low pressure, like high on a mountain top or in a plane.
Soft drink manufacturers add the CO2 to give it a tingle when you drink it. It also provides the foam on top of the drink that you can see. The foam that you see comes from all of the other ingredients dissolved in the water to make the soda. Syrup, coloring, and sugar are other significant ingredients in soda. They make the soda thicker so that bubbles form when the gas is released. An interesting experiment is to open regular soda and diet soda and pour them into a glass with ice. You will observe that the diet soda bubbles more. Why? The diet soda doesn’t have as much syrup and sugar, so the gas comes out easier and faster.