When I was teaching chemistry during my first year, it was in an old art classroom. So when it comes to kitchen chemistry labs I consider myself an expert. I’m also pretty good at green chemistry labs. Those have largely harmless chemicals, which is what you get from teaching chem in an old art room. You know, the “getting scrappy” concept… I have two labs activities that are perfect for teaching heat flow that don’t involve a calorimeter! (Thank goodness)
I love a calorimeter as much as the next girl, but at the high school level? The error is just ridiculous. To the point that it’s almost not worth doing. So here are my two labs that I think are absolutely perfect for teaching heat flow and could be done in nearly any classroom.
Elephant’s Toothpaste Lab Activity for Teaching Heat Flow
First up is the Elephant’s Toothpaste lab. Now I typically teach this with kinetics. I more so focus on the catalyst aspect of this reaction. In case you’re unfamiliar, yeast is used as a catalyst to remove oxygen from hydrogen peroxide. This happens in a soapy solution, resulting in a foam, that can look like toothpaste coming out of a bottle. Because the reaction is so large, it’s toothpaste fit for an elephant. We often mix the reaction mixture with some food coloring to add excitement.
The reaction is pretty exothermic. In fact, you can sometimes see steam (slash oxygen gas) coming off the reaction. I have the students measure the temperature before and after. They describe that the reaction was exothermic, releasing heat to the surroundings, or in other words the foam they created.
This lab is a bit more technical in terms of heat flow, but that’s not really a problem for me and my chemistry students. For my physical science students, this is certainly fun. Unfortunately they don’t get the “whole” picture when we do this lab activity. For that reason, I prefer this next heat flow lab activity for physical science students. (But of course, I also love it for chemistry.)
Freezing Point Depression Ice Cream Lab Activity
This next lab is a crowd pleaser for sure! It’s my freezing point depression lab. And again, I teach this in a deeper academic context for my chemistry students, and a bit more gentle for the physical science students.
A milk + sugar mixture is put in a plastic storage bag surrounded by ice and salt in a larger zipper bag. The salt helps to drop the freezing point of the ice, assisting the milk in freezing. The bag is shaken to create air pockets that prevent a “milk ice cube” from forming and instead a soft serve style ice cream. Read more about specific lab instructions here.
For my physical science kids, I do mention the concept of dropping the freezing point, but we primarily talk about heat flowing from high to low. The milk mixture, though cold, is actually warmer than the ice. Its heat leaves the milk and heads toward the ice, leaving the milk to become colder. Doing this while shaking creates air pockets that prevent a “milk ice cube.”
(I’m sorry I had to mention that twice, but it’s important that the kids know the purpose of the shaking. They otherwise complain ten times more. Trust me on this.)
Adding Real Life Context in Science Class
It’s always good to give some real life context to what we teach. And “opening the window on a cold day and letting the heat out” can only interest so much. When kids walk into class and ask “is this the class with the potions?” “When are we going to blow something up?” These kitchen chemistry heat flow labs do a far better job of keeping the students interested. And, seriously, who could hate on ice cream?!
