Expert: Profile Closed - 2/1/2010

Question
Hey I was wondering if Acetone reacts with water because when I mix them I see bubbles. Do the bubbles signify anything?
Thanks

Answer
Hi there, and thanks for your question.

There is no chemical reaction occurring when acetone and water mix; being polar, the acetone simply dissolves in water.

There are two immediately possible causes of the bubbles you saw;

1) When you pour one liquid in to another, the liquid being poured entrains some of the air it falls to in to the receiving liquid - so, for example, as you pour acetone in to water, the turbulence of the falling acetone, and of the "splash" when it hits the liquid surface, drags some air below the surface of the water. As the solution stabilizes, the buoyant air will rise to the surface - in the case of gentle pouring, this is very likely to be in the form of small pockets of air, making small bubbles. Similarly, stirring a mixture to make sure it's mixed can entrain air.

2) Whenever a substance dissolves in a solvent, there is a temperature change associated with the change in molecular structure. So, for example, when sulfuric acid is dissolved in water, the resulting heat is enough to boil the solution. In other cases, there can be a drop in temperature, as happens when salt (sodium chloride) is dissolved in water.

There is no way of knowing beforehand whether a solvent - solute mix will get hotter or colder when mixing happens, you have to do an experiment. The following paper, on acetone-water properties, suggests that when acetone and water are mixed, they give off heat: http://www.springerlink.com/content/1641302271221p13/ . If this is the case, then the solution they form will be quite warm, warmer than the starting liquids. You may remember that a liquid can dissolve more gas at lower temperatures, and that as the temperature rises, dissolved gases tend to bubble out of solution. It is possible, then, that dissolving acetone in water generates enough heat to force some of the air naturally dissolved in the water out of solution, again forming bubbles. I have yet to verify the report in the above paper by doing an experiment myself, so I offer it only as a useful possibility.

Hope that helps, and if you have any further questions, just send a follow-up.

Best wishes,
George