If you’re like my weisenheimer spellcheck, you might have noticed a stray “e” in the title above. If so, like my spellcheck, you’re wrong. This Demo Science experiment is not about blessed tap water—instead, it’s about the holes in water that we can’t see. “Say what now?!” you ask, dubious. Don’t worry, all shall be revealed… with science!
Forget the Bucket, There’s A Hole in My Water
Your students may not believe it, but there are pockets of “open” space between the molecules in water. Follow these easy steps to show the smelly little buggers how that works. For starters, you’ll need a good-sized, clear glass jar, some tap water, some rubbing alcohol, a one-cup measuring cup, masking tape, and a marker or pen. (If so inclined, you can skip the tape and use a pen that’s made to write right on glass. It’s a horse apiece, really.)
Start by affixing a vertical strip of tape to the outside of the jar, reaching from top to bottom. Then, pour one cup of water into the jar and mark its location on the tape strip with a horizontal level line and a “1”. Add a second cup of water, and mark its level with a “2”. Dump out all the water and dry the inside of the jar (I guess you’ll need a towel, too).
Measure out another cup of water and pour it into the jar. It should, of course, reach the “1” mark on your tape. Next, measure one cup of rubbing alcohol and add that to the jar.
If your students are paying attention (Kevin!), they’ll notice that, though you’ve just added two cups of liquid to the jar, those two cups of liquid do not reach the previously established two-cup mark. What the science is going on here?
It’s All About Them Molecules, Man
Left to its own devices, water will maintain small “pockets” of space betwixt its molecules. This is attributable to the polar nature of water molecules, and the angles at which they form. Rubbing alcohol molecules are smaller than water molecules, and so, when the two are mixed together, the alcomolecules will infiltrate the water molecules and slip into those little pockets. In this way, two cups of liquid become less than two cups of liquid.
The same experiment, performed with other liquids, would not provide the same results.