A lab activity on changing phases would be a major waste of time if you were using heat to change state. Students already know the outcome. I mean, unless you were doing calorimetry. But even then, I’m not a fan because in high school the equipment gives a huge margin of error. This lab activity instead shows students the effect of pressure on phase of matter. And it’ll be a lot of fun!
Oobleck
There’s a Dr. Seuss book on a substance called Oobleck. I’ve read it to some of my classes! Many teachers have determined that the “official recipe” for oobleck is cornstarch and water. It’s easy to dye, moderately easy to clean up and tons of fun!
“Oobleck” is a Non-newtonian fluid, which means that it doesn’t quite follow the rules. That’s because when it’s under enough pressure it’ll act like a solid. Well that’s true for most liquids, but this substance doesn’t require a lot of pressure. In fact, there’s plenty of videos online of “oobleck” doing weird stuff.
Oobleck Recipe
Typically when we do this lab, I make the oobleck. I find that it’s easier to just leave the students out it. They come to class with completed oobleck. I typically make 4-5 pounds of the mixture, and put it into aluminum baking or roasting pans. The ones that your mom might consider disposable, but your grandma wouldn’t. You don’t have to use food coloring, but it’s probably best to do this with high school students.
Dye the water and add to your dry cornstarch. For every two cups of cornstarch, you’ll need one cup of water. (Just buy the cheap, store brand stuff from your grocery store). You may need to add a bit more water over the course of the school day. Handling the mixture can cause it to dry out a bit. You’ll know it’s perfect when you can pick it up and roll it into a ball in your hands. But when you stop rolling it, it will return to liquid state and flow through your fingers.
Manipulating Oobleck
I give the students a lab form for them to record their observations. And I have them write a conclusion about oobleck and the effect of pressure on phase of matter. They use this lab outline. Mostly the kids are instructed to play with oobleck. This makes for a REALLY fun lab activity where students get to mostly play with science. And those are some of my favorite labs! I mean, chemistry is really tough. I feel that it’s very important to get students excited about science by just taking the time to have some fun!
Cleaning Up
You can run this cornstarch and water mixture down the drain. But you have to be careful, because it can clog the drain very easily. The best bet would be to dilute the mixture first, and pour it down the drain with running water. This is true for washing hands too! Use loads of water.
I prefer to leave my trays of oobleck sitting out overnight to dry up a bit. Then I just throw them in the trash. If you’re able to save your aluminum trays, you can usually scrape the oobleck out and rinse the tray!
