|MadSci Network: Chemistry|
To begin with... it was not a vacuum for long. Huh? Well lets begin at the beginning. Water; a polar molecule, structure O-H | H The oxygen is negative and gloms onto positive particles, while the hydrogens are positive and glom onto negative things. When water is just with water all the molecules are a certain distance from each other giving water its particular density. O-C4H9 (see your book or science teacher for a more explicit structure) | H In the isoprpyl alcohol the OH end is like water, and therefore acts just like water, glomming on to passing positives and negatives. The "organic" portion - the C4H9 is non-polar and is ignored and repelled by the water and/or the other OH parts. And again when isopropyl alcohol is with just other isopropyl alcohol, all the molecules are a certain distance from each other giving the alcohol its particular density. Now when the water and alcohol are first poured into the test tube they haven't really mixed, so the test tube is filled up with a layer of water and a layer of alcohol. The test tube is shaken, and the water and alcohol mix. The organic end of the alcohol allows the water and alcohol to snuggle in closer with each other than they would with themselves (water to water or alcohol to alcohol). The result; the water alcohol mix takes up less space than the two separate liquids... makeing that space at the top of the test tube. Now why did I say that the space wasn't a vacuum for long? Well, the very instant it formed... it was a vacuum. But any liquid faced with a vacuum will instantly turn to vapor to fill up the vacuum. So as soon as the vacuum formed, a little bit of the water and alcohol turned to gas and filled in the space. You couldn't see it because gas is invisible to the naked eye If you were to get curious about liquids filling in vacuums... go look up Raoult's law. I will concede that the pressure inside the space was probobly quite a bit lower than the air pressure outside the testtube (regular air pressure). So - closer to a vacuum. That was a great demonstration you saw... it deals with a huge number of chemical and physical principles. Good Luck! Greta Hardin
Try the links in the MadSci Library for more information on Chemistry.