|MadSci Network: Chemistry|
Well I did not see you proffer a theory in your experiment, just the empirical results. However, everything you observed and your conclusions are more or less correct.
You did not say how much boiling water remained in the soda can right after you boiled it, however at that point, the volume in the soda can that was not taken up by water contained heated water vapor. The pressure of the vapor at that temperature was not lower than atmospheric pressure (in fact it was equal); but when you upended the can into a pan of cooler water, the vapor cooled down, and at its new temperature definitely had a lower pressure than atmospheric pressure. At that point the pressure differential between inside the can and outside caused a vaccuum in the can sucking up the water in the trough (alternately you could say the atmosphere pushed the trough's water into the can). The amount of water sucked up from the trough would be proportional to the volume of the heated water vapor still left in the can when you placed it into the cold water.
Gay-Lussac's Law (also known as Charles' Law) simply says that the volume of a gas is proportional to its absolute temperature (measure usually in Kelvins), presuming that the same amount of gas is in both measured temperatures/volumes. see Charles Law (Gay-Lussac's Law)
This law is applicable to your experiment insofar that when the temperature of the water vapor gas was reduced, the volume of the vapor was also reduced. The actual calculations/theory is somewhat complicated in this example because water vapor doesn't remain a gas but becomes a liquid in this experiment. If you had used just air it would be a little closer to theory. But not as dramatic, since the air would always take up more volume at the end of the experiment than water vapor.
Try the links in the MadSci Library for more information on Chemistry.