Drooling Pumpkin Chemistry Lab for Halloween

 

In this Halloween chemistry lab, students create a jack-o-lantern that foams at the mouth! You can use the lab to address NGSS standard MS-PS1-2 as students observe properties of the reactant (hydrogen peroxide) and the bubbly products of the reaction.

I have used the "drooling pumpkin lab" with students in seventh and eighth grade. The class size has usually been about twenty-five students, and there has always been another adult in the room with me. This is helpful for managing materials and spills and to keep an eye on safety because sharp tools are required to carve the pumpkins. Students usually keep their behavior in check because they are excited to do the lab and know that safe behavior is a requirement for participation.

Students work at tables in pairs or small groups. They start by carving their pumpkin into a jack-o-lantern.

Before carving the pumpkins, be sure to put them onto a tray or paper to protect the tables because it gets messy! Suggest to students that positioning the jack-o-lantern's grin lower on the pumpkin will help the reactants flow out of its mouth. (After carving the pumpkins, you will have lots of seeds, so you could ask parents ahead of time if they would like to take some home to roast in the oven.) Depending on how much time you have with students, carving the pumpkins alone can take a full class period.

The reaction used to create the foam that oozes out of the jack-o-lantern's mouth is the decomposition of hydrogen peroxide, a liquid easily found in solution at pharmacies. Yeast is used as a catalyst in the reaction, so this is a good opportunity to teach students how a catalyst does not take part in the reaction but merely helps it happen. (I found a one-pound bag of yeast online and stored it in the freezer for many years.)

To activate the yeast, student groups mix a few tablespoons of yeast with a few tablespoons of lukewarm water in a small container and let it sit for about 5 minutes, forming a paste. Meanwhile, students pour about 1 cup of hydrogen peroxide solution into another small container and mix in a few drops of dish detergent. (I recommend using an unscented soap for students sensitive to smells.) The dish detergent will capture the bubbles produced by the decomposition of hydrogen peroxide, creating a foam.

Students lower the container of hydrogen peroxide solution with dish detergent into the jack-o-lantern, add the yeast paste, and stir. Soon, the reactants flow out of the pumpkin's mouth, causing it to drool! In some cases, positioning the container of hydrogen peroxide close to the jack-o-lantern's mouth can help students get this effect.

So, where did the bubbles come from? Yeast speeds up the decomposition of hydrogen peroxide into hydrogen and oxygen, and these gases are captured by the soap, creating the foam. Students can easily see that a chemical reaction has occurred!

If you are interested in other fun chemistry labs, you might like this blogpost on making "gel worms":

https://www.scientificcreative.com/2022/05/polymer-lab-gel-worms.html

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