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Oozing Pumpkins: Creepy Halloween STEM Fun

Creepy Halloween STEM Fun with pumpkins.

Halloween is a great time for the spooky, the messy, and the science.  Yep!  Science time!  Having a theme like this fun holiday to tie into a project really brings the lesson alive for kids.  Add to that the fact that Halloween is perfect for the ooey gooey, icky creepy activities.  Oh, and eruptions.  Yeah, that isn’t Halloween specific really.  But kids always love explosions.  Grab some pumpkins and let’s learn three ways to make your pumpkins ooze.

Small pumpkin with red foam coming out of the top.

Halloween STEM: Oozing Pumpkin Experiments

The goal of these experiments is to show your children some easy chemical reactions and of course, add in some holiday fun.  The great thing about these is you can do them over and over!  Just rinse out your pumpkin between experiments and try again!  There is no damage to your pumpkin.

Here are the three reactions we are going to look at:

  1. Baking Soda and Vinegar.  It’s a classic for a reason.
  2. Hydrogen Peroxide and Yeast.  It creates a thicker foam that is great to play with.
  3. Alka-Seltzer and Dish Soap.  This is the fastest to put together for when you need something fast!

The Pumpkin:

We used small pumpkins for our reactions.  They are cheaper and we don’t always actually carve pumpkins.  (Ben is just finally old enough to have the patience for a full jack-o-lantern.)  I have also found that the reactions are more impressive without having to use a ton of reactants.  So keep that in mind when you look at the measurements.  Scale them up for bigger pumpkins.

Whatever size pumpkin you decide to use, cut off the top and scoop out the seeds like you normally would.  Carve a design or face in or not, that is your choice.  (Though be sure not to carve too close to the bottom. Leave a couple of inches for the reaction to start in.)  And as I said, these won’t hurt your pumpkins!  Just rinse them out and you can still set them out for Halloween night.

One final big tip: Secondary containment.  Be sure your pumpkin is oozing while sitting in a container or outside.  The eruptions are easy to clean and safe, but they will spread out quickly if not contained.  I don’t like to make extra messes for myself, so I keep the pumpkins in a container.

Preschool boy playing with red foam from a pumpkin with text overlay 'Easy and fun sensory Halloween STEM for kids'

The Classic Volcano Ooze

The first way to make your pumpkin ooze uses a classic eruption recipe.  Baking soda and vinegar.  This is one of my favorites because it is such a classic.  And I always have these items on hand.  They are fast and safe to use.

You Need:

  1. Baking Soda
  2. Vinegar
  3. Water
  4. Dish Soap

To Do:

Take your cleaned out pumpkin and put about 2/3 to 3/4 cup of water into the bottom.  Mix in 5 tablespoons of baking soda and a healthy squirt of dish soap.  If you want colored ooze then add a few drops of food coloring.  Gently make sure everything is mixed well.

To make your pumpkin ooze with ickiness, pour 1 cup of white vinegar into the mixture in the pumpkin and stand back!

The Science:

The baking soda and vinegar are the two reactants we are looking at here.  The combine and one of the products is carbon dioxide.  This gas is what creates the bubbles that ooze out.  The dish soap works to trap the carbon dioxide and create more and bigger bubbles. (Get more vinegar and baking soda activities—> Baking Soda and Vinegar Activities for Kids)

vinegar and baking soda chemical reaction

The Sensory Foam Ooze

This oozing pumpkin is courtesy of elephant toothpaste.  Yep, this fun foam can be added to your Halloween activities.

You Need:

  1. 3% Hydrogen Peroxide
  2. Water
  3. Dish Soap
  4. Yeast
  5. Food Coloring

To Do: 

Mix 2 tablespoons yeast with 3 tablespoons warm water.  It will be thick, but mix it as best you can and set it aside.

Pour 1 cup hydrogen peroxide into your pumpkin.  Add a nice squirt of dish soap and the food coloring of your choice.  Mix them all together.

When you are ready for your pumpkin to ooze like crazy add the yeast mixture to the pumpkin.  Be careful, the reaction will happen quickly!

This is an exothermic reaction, meaning the foam that results will be warm.  Don’t worry, it isn’t hot enough to be dangerous, but do know it is supposed to be warm.  This creates a thicker foam that is awesome for kids to play in, so be sure to do this reaction in a bigger container so you can enjoy the result!

The Science:

The hydrogen peroxide in this reaction is broken down into water and oxygen.  This normally takes a long time to happen.  The yeast is used to speed up the reaction.  It’s called a catalyst, which is a substance that increases the rate of a reaction without being changed itself.  And the dish soap again helps trap the oxygen to make great bubbly foam.

A lot of elephant toothpaste recipes call for 6% hydrogen peroxide.  This is a stronger concentration than you find in the store, but you can order it online.  However, I use the 3% hydrogen peroxide you can just buy at Target and it works just fine.  Yes, the foam will be bigger and thicker with the higher concentration, but it is still pretty great with the lower one.  So feel free to use the easier to get hydrogen peroxide. (Learn more about this reaction—> Elephant Toothpaste: A Fun Sensory Explosion)

The chemical reaction for elephant toothpaste (hydrogen peroxide to water and oxygen) used to create an oozing pumpkin for Halloween STEM fun

The Fastest Ooze 

This last reaction is super fast to put together, which makes it a good one.  It’s also an easy one to do little experiments with to compare the size of the reaction.

You Need:

  1. Alka-Seltzer Tablets
  2. Water
  3. Food Coloring

To Do:

Fill the bottom of your pumpkin with water.  Add your food coloring to mix.  Break up 2-3 Alka-Seltzer tablets and drop them in.  Let the foaming begin!

This method makes a thinner foam, so it isn’t as easy to play with.  But it makes a big impression, especially when done in a small pumpkin.  What makes this method so great is that the reaction happens very quickly.  It can be done over and over, just add more tablets!

This is one of my favorite ones to actually experiment with.  What gets a bigger result, just putting in a whole tablet or crushing the tablet first?  Does more water make it bigger or smaller?  Let your child take the lead on this. It’s also a great one for a big impact if you just throw a ton of Alka-Seltzer in!

This is by far the easiest way to make your pumpkin ooze, and it doesn’t create as great of a reaction as the other ways.  But the good part of this one is that it travels well.  If you are going to a Halloween party or want to be able to do this on the go all you need is the water and Alka-Seltzer and you can do this one anywhere! (For more fun with Alka-Seltzer try this—> How To Make an Easy At Home Rocket)

The Science:

Alka-Seltzer contains sodium bicarbonate and citric acid.  Yep, the same two basic ingredients from our first oozing pumpkin.  These tablets contain both the baking soda and acid (vinegar is an acid) needed to create a foaming reaction.  All that it needs to start is the water.

Chemical Equation of Alka-Seltzer when it reacts with water


Now, all these reactions are pretty safe.  I let my kids touch them.  But please keep in mind basic safety.  Don’t let your children eat or drink any of the components.  Don’t let your children get any components of these reactions in their eyes and be sure they wash their hands after playing with any foam created.  Again, this is just basic safety and precautions that should be taken anytime you are experimenting with chemical reactions.

Pumpkin with red foam oozing out with text overlay stating STEM for kids! How to create oozing Halloween pumpkins

Halloween STEM

These are 3 easy ways to explore a little science with your Halloween.  They are all easy and fun.  You can learn about various chemical reactions and experiment to get the best reaction you can.  And there is nothing like watching some red foam ooze out of a pumpkin to really get you into the Halloween spirit.  Chemistry and creepy fun? That’s a Halloween win.

Here are some more fun STEM activities to try!

Fast and Fun Fall Science Activities

Easy and Clean Sensory STEM for Toddlers and Preschoolers

The Big Benefits of Sensory Play and Easy Ways to Fit It In

young children carving pumpkins with text overlay '3 ways to make sensory oozing pumpkins'

Halloween STEM and Learning Activities

Easy and fun STEM and learning activities perfect for Halloween!

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