View Full Version : agitation of solution

15th November 2008, 08:42 PM
This is more of a random science question but why when you agitate a solution some of it can become dissociated.
A simple example of this is shaking up a closed pop, some of the CO2 will come out of solution.

15th November 2008, 09:17 PM

While shaking the can does force a little gas from the soda, actually, shaking a pop can is more about putting bubbles into the soda than taking them out.

When you shake the can, you make the gas in the expansion space at the top of the can... ummm... froth... with the liquid contents. You can show that an insignificant amount of gas is forced out of solution because the pressure inside the can doesn't actually change much.

These bubbles are under pressure because the can is under pressure, right?

What happens to tiny, high-pressure bubbles when you take the pressure off? The bubbles expand into pressure equilibrium with the pressure outside the can. Big, fancy words for, "they get bigger."

Now, if this froth used to fit exactly inside the can when they were compressed, when they DEcompress, what happens? Remember, please, that the bubbles are spread all throughout the liquid, not just at the top, so when the bubbles down at the bottom expand... well...


Now, you can get some CO2 out of solution by putting a few grains of salt into the can. This provides what's called, "nucleation (http://en.wikipedia.org/wiki/Nucleation)," sites with which the CO2 can get busy and conglomerate enough to form bubbles large enough to float up and out of solution.