You've probably experienced it. You open your soda can, and fizz spilled over the top, and made a mess.
And you've probably also heard the advice: you should tap your soda can with your fingers or against something, so it won't overflow.
On first consideration, that seems like nothing but an old wives' tale. Any chemist will tell you that a can of soda fizzes because when you open it, the pressure inside the can drops from three times atmospheric pressure to normal atmospheric pressure.
The ability of carbon dioxide gas to dissolve in water decreases when the pressure decreases. The gas comes out of solution and forms bubbles that rise to the top and can sometimes cause the can to fizz over.
And, while that's all true, according to a chemist at Trent University in Canada, tapping your soda can really does work to keep it from fizzing over. This is because before you open the can, there are microscopic bubbles already clinging to its walls.
When you open the can and the pressure suddenly drops, these tiny bubbles become the nuclei for the formation of larger ones.
Dislodging Tiny Bubbles
If you don't tap the can, the microscopic bubbles are spread all over its inner walls, including its deepest parts. When they enlarge, they displace lots of liquid and cause the fizz to spill out of the can.
Tapping dislodges the tiny bubbles from the walls of the can, and causes them to rise to the top. Then, when the can is opened, all the fizz will be formed near the top and less fluid will be displaced. So, yes, keep on tapping those soda cans.
Sources And Further Reading:
- Gerbis, Nicholas. "Does Tapping a Soda Can Prevent it from Foaming Over?" LiveScience.com August 30, 2012. Accessed February 12, 2018.
- Hamlett, Chris. "Does tapping a can of fizzy drink really stop it foaming over?" TheConversation.com. June 14, 2016. Accessed February 12, 2018.
- "Why do people tap on soda cans before opening them?" HowStuffWorks.com. March 28, 2001. Accessed February 12, 2018.