Halloween Pumpkin Volcano Science Project

It’s fall and with fall comes Halloween and Pumpkins. Some years we grow our own pumpkins, other years I buy my pumpkins, but no matter how they arrive, it is always exciting when we get the first pumpkins of fall! This year we kicked off pumpkin season with a Harvest Pumpkin Battery project, then we jumped into a very exciting Puking Pumpkin Science Project! Kids love this erupting chemistry experiment we have affectionately nicknamed: Puking Pumpkin!

Puking Pumpkin Halloween Science

Halloween Pumpkin Volcano Science Project

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Halloween is the perfect time to experiment with pumpkins. There are so many fun ways to explore science. We start by making a battery with our pumpkins and now we can use the same pumpkins for chemistry lessons the kids will never forget. Our puking pumpkin experiment is an awesome example of a chemical reaction. Kids love these amazing reactions just as much as adults, which makes this project a fantastic addition to your Halloween party! This vomiting pumpkin science experiment uses a baking soda and vinegar reaction for a classic chemical reaction.

This year we are putting our pumpkins to good use! It’s early, so we knew that any pumpkins we grabbed now would not make it to Halloween night. Especially since it is below freezing here and snowy. So we nicknamed these first two pumpkins “Science Pumpkins”! That means we are doing as many fun and interesting science activities as we can think of with these pumpkins with no worries about making them last for Halloween.

Puking Pumpkin Video

Check out the video of this easy Halloween science experiment. This video is also available on the STEAM Powered Family YouTube Channel.

First A Pumpkin Battery

Our first project was building a Harvest Fruit Battery using Pumpkins and Squash. It was a huge success, which actually surprised me. I was worried it wouldn’t work. But it did! And the kids had a blast with this Pumpkin STEM project. We even powered an LED with our fruit battery! So cool.

After our fruit battery stem project, it was time for a new pumpkin project.

Carving the Pumpkin

First up, I let my kids carve their pumpkins on their own for the first time. Normally we do all the cutting and they just remove the slimy guts, but they are old enough now to tackle it themselves. I was honestly very surprised how well they did carving the pumpkins. I admit I had to bite my tongue a few times, as I wanted to jump in and help, but they were careful and total pros.

Pumpkin Science Experiment For Fall

After that we washed the seeds and roasted them. Homemade roasted pumpkin seeds are the best!

So now we had carved pumpkins we needed another fun project.

It’s been really cold here and snowy, but the sun came out for a day and melted the snow. Since we could get outside, I decided to do a very messy pumpkin volcano.

And this is really, really messy. I don’t know if I own a bowl or dish that would have been big enough to contain our eruption. So do this outside. Seriously.

This was messy science at its finest!

The Puking Pumpkin STEM Project

This easy pumpkin science activity has been dubbed the puking pumpkin by my kids. Youyou may have seen other puking pumpkin projects using guacamole, but this puking pumpkin experiment with baking soda and vinegar is perfect for Halloween STEM! Which is perfect for STEM loving kids!

Puking Pumpkin Supplies

For this experiment you will need:

  • One carved pumpkin or Jack O’Lantern
  • Baking soda
  • Vinegar
  • Food colouring
  • Large plastic juice jug or a bucket works too
  • An outdoor space you don’t mind getting a little messy
Halloween pumpkin science make your pumpkin puke!

How to make your Pumpkin Puke!

Take your pumpkin outside and set it on a surface that is easy to hose off. We used an upturned bucket. If you want to try this inside I recommend using a large tray with deep sides.

Take the top off your pumpkin. Now add baking soda (about 1/2 cup should be right, but adjust as necessary for best eruption). Be careful it doesn’t poof right out the mouth!

Careful pouring the baking soda into the pumpkin volcano

In the juice jug mix vinegar with some drops of food coloring (or whatever colour you want). We used about 2 cups of vinegar. This experiment does not require you to be exact. So let the kids experiment with ratios and play.


Remove the top lid of your Jack O Lantern. Now slowly pour the vinegar into the top of the pumpkin.

Watch as your eruption starts, then pours out of the pumpkin’s mouth. Your pumpkin volcano looks like it is vomiting! Nothing like a barfing pumpkin. And if your kids are anything like mine this will lead to squeals of delight!

Puking Pumpkin

The Science of a Puking Pumpkin

Unlike our Lemon Volcanoes which erupted with just the addition of baking soda, we need to add an acid to our base (baking soda) in our pumpkins in order to create a reaction. Lemons are naturally very acidic, pumpkins are not. You can tell this just by tasting them or using a pH test. Pumpkins need help to start their eruptions, so we add acid (vinegar) in order to create the chemical reaction that results in our pumpkin eruption. You could also try lemon juice and baking soda and compare the results!

Puking Pumpkin Chemical Formula

The chemical reaction taking place in our puking pumpkin is:

CH3COOH (l) + NaHCO3 (s) = CH3COONa (l) + CO2 (g) + H2O (l)

Vinegar or Acetic Acid has the chemical formula CH3COOH. Baking soda is a base also known as Sodium Bicarbonate and has the chemical formula NaHCO3. During this reaction the products are sodium acetate (NaC2H3O2). Sodium acetate is made of 1 sodium ion, 2 carbon atoms, 3 hydrogen atoms, and 2 oxygen atoms. The other products are water (H2O) and carbon dioxide (CO2). Carbon dioxide is the gas that causes the bubbling during the reaction.

Pumpkin + Baking Soda + Vinegar = Puking Pumpkin! 

This activity was a ton of fun and the kids ran to grab more vinegar to keep our pumpkin volcano erupting over and over again. Give it a try next time you want to do one last thing with your pumpkin before it goes into the compost! Since we are using all natural foods for this chemical reaction, the pumpkin is still perfectly safe to compost.

Happy Halloween!

More Halloween STEM Activities

Don’t miss our 31 Days of Halloween activities. It includes the Puking Pumpkins plus many more STEM (Science, Technology, Engineering and Math) activities, Arts and Crafts, Recipes and more!

Halloween Activities

Halloween Pumpkin Science Experiment for Fall