Oozing Pumpkin Halloween STEM Activity

Mixing baking soda and vinegar is a classic acid-base chemical reaction. The vinegar (an acid) and the baking soda (a base) react to form carbon dioxide gas, which expands rapidly and creates millions of tiny bubbles. You can't usually see a gas, but here you can: the more carbon dioxide that's produced, the more the bubbles grow. That's evidence a chemical reaction really happened, a brand new substance, carbon dioxide gas, was formed. It's no longer just baking soda and vinegar.

On its own, that reaction would just fizz and pop away in a few seconds. The dish soap is what turns it into ooze: it traps the carbon dioxide inside thick, soapy bubbles instead of letting them burst right away, so instead of a quick fizz, you get a slow, heavy foam that keeps growing and spilling out of the pumpkin's face.

This same acid-base reaction shows up in plenty of familiar places. Fizzy soda, the glow inside a glow stick, and the fizz when a sour candy hits your tongue are all chemical reactions too, evidence that new substances are forming all around you, not just inside your pumpkin.

Try it yourself: Run the experiment again, but change only one variable at a time, more vinegar, more baking soda, or a bigger pumpkin, and predict how each change will affect how much the pumpkin oozes before you test it.