Chemistry Demonstrations Extraordinaire

Okay, maybe extraordinaire was a bit of an unrealistic term, but we have begun the study of gases in chemistry class, so I've decided on a couple of demonstrations to share with the class. Thought you might enjoy knowing that there is occasionally an ounce or two of fun in being a chemistry graduate student, contrary to popular belief.

1st Demo: This is actually for the previous chapter on thermochemistry (the transfer of heat energy from one system to another). I've decided to share an endothermic reaction (one that requires heat energy to "go" thus making the container feel cold - and example would be ammonium nitrate dissolved in water - this is what is in an athletic "instant cold pack"). I'll give a student two vials, each with a different solid. One has ammonium thiocyanate and the other has barium hydroxide octahydrate (doesn't matter if you don't have a clue what these are). What's cool is that when the students mix them together in one vial, they will begin to melt and dissolve into one another, and the vial will get extremely cold (below the freezing point of water), and actually cold enough to freeze the vial to a waterlogged piece of wood...can't wait to try it.

2nd Demo: Demonstrating the fact that increasing the amount of gas in a balloon will cause the volume to increase. Okay, this sounds incredibly obvious and mundane (and it is), but it will be cool because I will weigh out different masses of dry ice (solid CO2) and place them in an empty balloon and tie the balloon. The balloons will then inflate on their own as the CO2 sublimes, and we will be able to predict the volume of the gas in the balloon from the mass of the dry ice - and then check our calculations by actually finding the volume of the balloon. This is done by dunking the balloon in a completely full-to-the-brim bucket of water so that the water that spills out is collected and measured and that will be the volume of the balloon...very cool indeed.

3rd Demo: Demonstrating the fact that decreasing the temperature of a gas will decrease its volume. This was is great because I will have a student come up and inflate a balloon and tie it off. Then, once inflated I will have them place it is a styrofoam cooler and I will pour liquid nitrogen (T = 77 K = -196 deg C = -320.8 deg F) on the balloon and it will shrink (the gases will condense to a much smaller volume (and many will actually change to liquids when they are that cold). Pulling out a small, shriveled balloon, I will lay it on a table, and then as the balloon warms, it will re-inflate! It will be spectacular I'm sure.

Hey, I can't help it if I get excited about this stuff, I'm a dork.