Don’t you hate it when you see a cool demo, but have no place for it? That is the way I felt about the exploding gummy bear demo. It’s cool. But I never did it because I want everything in class to be tightly tied to the content. And I couldn’t find a home for the gummy bear. Until now.
In my grade-level chemistry class, we are just discussing the evidence for a chemical change versus and physical change. This is the perfect place for the gummy bear demo. Before the demo I have students brainstorm ideas for how to know that a chemical reaction has taken place. Each kid has to come up with three. Then they take their list back to gather around the fume hood.
I take an old test tube and fill it to a depth of about one inch with potassium chlorate. Then I start heating the compound. As it is warming up, I have the students talk about the inter-atomic distance and how it is changing as it melts. Then I ask if they think what they are watching is a chemical or physical change. They all say physical because it just appears to be melting. However, if you look closely, you can see that there are some bubbles being released once the majority of the solid has melted.
That is when I ask if anyone had “releasing gas” as part of their chemical reaction list. A few will. Then I ask how we could know if this is a chemical reaction taking place. After sorting through some answers that we can’t test, someone will bring up the most basic fact in a chemical reaction.
If the substance at the end of the process is a different substance, then there must have been a reaction. But how will we know if it’s a different substance. I can generally guide them toward testing the behaviors of the substance. If the behaviors are different, then the chemical is likely different.
That is when I throw a gummy bear into a beaker that contains solid potassium chlorate. Nothing happens. It just looks like the bear was reclining at the beach and is all sandy.
Then I take the gummy bear out and throw it in the test tube with the molten potassium chlorate. And we watch the beautiful demise of the gummy bear. The purple flames shooting out. The smoke boiling into the fume hood. The bear jumping around in apparent pain.
What do you think? Was the solid at the beginning and the liquid after heating the same substance? No. Because it behaved wildly differently. Then we head back to our seats and see how many of the evidences of a chemical reaction we observed. Depending on your list, it’s almost all of them.
I show them the equation for potassium chlorate decomposing into oxygen and potassium chloride. We look at the charred remains of the gummy bear. We talk about reversibility. The concepts seem to come together around a really cool looking demo.
Finally, the violent death of a beloved candy has a curriculum home. Identifying chemical and physical changes. Give this method a shot, I think it will have a home in your class and your students’ minds forever.
Obligatory caution: This demo gives off a ton of smoke. It gets really hot. It splatters molten ionic compounds around. I only do this in a fume hood. Never with kids standing around exposed. Also, don’t try to save the test tube after. Just throw it away.
Want to try a different way to engage your students with less fire and candy-death? Try curriculum centric games from Stoich Decks! Intro the mole with Up & Atom. Teach ionic formulas with CHeMgO, the game with four different levels of challenge to serve your students. Or use Trendy to help students identify periodic trends. Check them out today.
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