Mix up a bubbly brew in a potions lab fit for any little wizard or witch with an awesome Halloween chemistry experiment. Super simple household ingredients create a cool Halloween themed chemical reaction that is just as much fun to play with as it is to learn from! Create a season filled with clever, spooky, creepy learning opportunities with our 31 days of Halloween STEM Countdown!

Explore Chemistry For Halloween

This fall season we are exploring some cool Halloween chemistry experiments. This exothermic chemical reaction using hydrogen peroxide and yeast is lots of fun and super easy to set up.

Although a bit messy, it also has a terrific sensory play element built right in. Make sure to check out our zombie slime for more cool Halloween chemistry science experiments.

The reaction between the hydrogen peroxide and the yeast makes this awesome foam that is perfectly safe for little hands to play with and a breeze to clean up. This is NOT edible! We love cool fizzing, foaming, erupting chemical reactions.

Check out the awesome photos below and at the end, you will see everything you need to set up your own Halloween chemistry experiment.

This classic chemistry experiment is often called elephant’s toothpaste because of the voluminous amount of foam that it usually produces. However, you do need a much stronger percentage of hydrogen peroxide to produce that reaction.

You can still enjoy the same type of chemistry experiment but with less foam and less of an exothermic reaction with regular household hydrogen peroxide. The experiment is still awesome, and if you get a chance to try the higher percentage of peroxide, it will be worth it too.

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Tip: Add Some Food Coloring

Food coloring is a super simple way to give science a holiday theme. My son is also very generous with his food coloring use. The simple stuff from the grocery store works just fine.

Plus you can easily pick up the other ingredients on your next shopping trip. Check your cabinets first. That’s the best part of kitchen science.

Hydrogen Peroxide and Yeast Reaction

The reaction between the hydrogen peroxide and the yeast is called an exothermic reaction. You will feel warmth to the outside of the container because energy is being released.

The yeast helps to remove the oxygen from the hydrogen peroxide creating tons of tiny bubbles that made all that cool foam. The foam is just the oxygen, water, and dish soap that you added.

If you pay close attention, the reaction continues for quite a while and looks quite different depending on the size of the container you use! Experiment with different sizes! We chose three different size flasks for our wizard’s brew. Each one looked pretty cool.

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Get your free printable Halloween activity guide!

Halloween Chemistry Experiment


  • Hydrogen Peroxide
  • Warm Water
  • Yeast Packets {we used two packets for the three beakers}
  • Flasks or Plastic Bottles
  • Teaspoon and Tablespoon
  • Food Coloring
  • Dish Soap
  • Tray or Container {to place bottles or beakers on to catch foam}
  • Small Cup {mixing yeast and water}


STEP 1. Pour the same amount of hydrogen peroxide into each container unless you are just using one container. We used a 1/2 cup.

STEP 2. Squirt dish soap into flask or bottle.

STEP 3. Add food coloring {as much as you like, my son is very generous}.

STEP 4. Mix 1 teaspoon of yeast with 2 tablespoons of warm water. It was clumpy and didn’t mix perfectly but that’s fine!

STEP 5. Pour the yeast mixture into the container and observe what happens.

Notice how quickly the reaction begins. The foam had started before he was even finished pouring in the rest of the mixture.

For the larger flask, the reaction continued for quite a while inside the beaker before it came out of the top. Would a different amount of hydrogen and yeast change that?

Now, this isn’t like a baking soda and vinegar chemical reaction where the reaction is more instantaneous. This takes a little bit longer, but at least you get plenty of time to observe the changes.

You can see we are using our smallest flask for some of our Halloween chemistry experiment above and below. Because it’s the smallest, it happens to be the most dramatic.

However, make sure to notice what happens with the large flask. Although not super dramatic, it looks pretty cool.

And for the grand finale, foam everywhere. Remember I said to take a look at the large flask? Notice the difference?


Go ahead and play around with the foam. My son added additional red food coloring. This will temporarily stain the hands if you use as much as my son! If we stayed with the pink foam this would not have happened.

You can also go ahead and whip up new yeast mixtures and add it with extra hydrogen peroxide to the already foamy bottles or flasks. We always do this with our baking soda and vinegar reactions!

More Spooky Halloween Experiments

Check out our complete list of spooky Halloween science experiments for kids!

Bonus Halloween Art Activities

Go ahead and add some of these favorite Halloween art activities to your countdown!

Printable Halloween STEM Activities Pack

150+ Pages of Halloween-Themed Materials!

This Halloween project pack is suitable for home, school, and group use for kids in grades Kindergarten through elementary but is scaleable for many ages and abilities.

What’s Included:

  • 25+ Halloween theme science and STEM activities with printable sheets, instructions, and helpful information all using easy-to-source materials perfect for limited-time needs. Includes a Halloween engineering pack with fun, problem-based challenges for kids to solve!
  • The skeleton activity pack includes building a skeleton challenge and a coding challenge! Try a skeleton bone bridge-building STEM challenge!
  • Halloween theme brick printable activities for hands-on learning with math that is perfect for early finishers or home fun and reinforces basic math concepts.
  • Bonus fun pack includes games and activities to round out your Halloween theme, such as I Spy, bingo, matching, Would You Rather cards, scavenger hunt, word search, A-Z Halloween hunt, and a coloring page.
  • The Halloween STEAM Pack includes artist-inspired projects by Warhol, Lichtenstein, and more!