The phases of matter are almost too easy for high school chemistry. But somehow we always wind up teaching them! Well I find that many of students have a pretty easy time with identifying the states of matter – that’s no problem. But the issue is figuring out how the phases of matter change. Many of the students believe that water must boil in order to evaporate. I have a changing phase of matter activity that focuses on the effect of pressure. Most kids do know the phase changes, but a lot of the time they struggle with some of the advanced concepts like vapor pressure and change in pressure. My changing phase of matter activity is A LOT of fun!
Oobleck Lab for Phases of Matter
Oobleck is actually the name of a book written by D. Seuss. It has very little to do with chemistry. But a mixture of cornstarch and water has been given this name. You make “oobleck” by mixing about ¾ cup of water with 1 cup of cornstarch. If coloring the mixture, make sure to add it to the water before mixing with the cornstarch.
Properties
The cornstarch water mixture has some interesting properties. When under pressure, the mixture can behave like a solid. You can roll it and form it into a ball. When it’s in a pan, you can apply quite a bit of pressure and it’ll feeling like pushing onto the surface of your lab bench. If your hand is trapped under the surface, if you try to pull it out too quickly it’s like your hand has been cemented into the pan.
When this mixture is under very little pressure it’ll behave like a liquid. If you lightly scoop it up it’ll run through your fingers. Tilt it out of a cup and it’ll pour out like pancake batter. Now, this is a heck of a lot of fun, but what does it have to do with chemistry class?
Relating to Changes of Matter
Like I had mentioned, many of the kids already know that heating or cooling can change phase. But what they don’t know (or usually don’t realize) is that a change in pressure can also change the phase. Now I’ve never worked in a school that had a functional bell jar and vacuum pump combination. It’s kind of necessary to see the triple point of water… I mean, you can make it happen other ways but that certainly wasn’t going to happen with my lab set ups. So when it came to really diving in on teaching my students about matter being able to change phase based on pressure oobleck came to the rescue.
Other Uses
I have used this lab obviously for teaching chemistry and changing phase of matter. But I have also used it for teaching my physical science students how to write lab reports, how to conduct themselves in a lab and how to identify variables. It’s more so to get my students used to the lab expectations than anything else. I want them to get familiar with writing things like “When I manipulate oobleck [like this] it responds by behaving [like that].” It’s a great lab for introduction to what I call “Big Boy, Big Girl, Big Scientist” writing. When you grow up (and get to high school experiments) the requirements for how you write change quite a bit. Get a copy of my lab report rubric here!
All in all, this lab is really a fun time. The kids LOVE it and we call back to it very often. I love that I can get my students to very easily see the affect of pressure on the phase of matter and even get them writing like scientists.
