Looking for a Halloween science activity for kids that bubbles, foams, and sparks their imagination? Turn a few household ingredients into a bubbling witch’s brew!
This simple experiment combines science with creativity. Kids can choose their potion’s colour, invent a spooky name, and discover what makes the foam rise. Best of all, you only need a few kitchen supplies—and a tray to catch the bubbling brew.
How to Make Your Bubbling Witch’s Brew
First, place a small plastic cup or open container inside a deep tray or baking dish. This will be your miniature cauldron.
Next, follow these steps to bring your potion to life:
- Add 1 tablespoon of baking soda to the container.
- Then add 1 teaspoon of liquid dish soap.
- Pour in 1 tablespoon of water and a few drops of food colouring, if you’re using it. Stir gently.
- Next, measure ¼ cup of white vinegar into a separate cup.
- Finally, ask your child to predict what will happen. Slowly pour the vinegar into the cauldron and watch the foam rise!
Green makes a classic witch’s brew, but purple or orange can be just as spooky. The amount of foam will vary with your container and dish soap, so watching what happens is part of the experiment.
Once your brew starts bubbling, watch how high the foam rises. Does it stay inside the cup or spill into the tray?
What Makes the Witch’s Brew Bubble?
The bubbling begins when vinegar and baking soda meet.
Vinegar is acidic, while baking soda is a base. When they react, they produce carbon dioxide gas. That gas forms bubbles as it escapes from the mixture.
The dish soap traps some of the gas inside bubbles. As a result, foam builds up and your witch’s brew rises!
As the reaction continues, ask your child to look closely. Can they see tiny bubbles? Does the foam grow quickly or slowly? Afterwards, notice what happens when the bubbling stops.
Those observations are the beginning of a science investigation.
Dish soap traps gas bubbles, creating the witch’s brew foam.
Add a Little Art to Your Halloween Science Activity
Now that you’ve explored the science, it’s time to give your potion a personality.
For your next batch, invite your child to create a paper label before mixing the ingredients. Attach it to the outside of the container, above the tray’s spill line, to help it stay dry.
Will they make Dragon’s Burp, Monster Bubble Bath, or The Incredible Fizzing Pumpkin Potion?
Before you begin, they can also draw what they think their brew will look like. Afterwards, compare the drawing with what happened. Was the foam taller than they expected? Did the colour look different?
Turn Your Potion into a STEAM Challenge
To investigate further, explore a new question: What changes how much foam we make?
Try two fresh batches using the same quantities of baking soda, vinegar, water, and food colouring. Add dish soap to one batch. However, leave it out of the other.
Before you begin, ask:
- Which batch do you think will make more foam?
- Will both batches still bubble?
- How could we compare the results?
Use identical containers so the comparison is easier. Then place a ruler beside each container so older children can record the highest foam level. Meanwhile, younger children can draw the two results.
Most importantly, change just one thing at a time. This helps your child investigate what caused the difference.
Small Bubbles, Big Learning
This Halloween science activity gives children several ways to practise STEAM skills.
First, they explore science by watching a chemical reaction. They also use math to measure ingredients and compare foam heights. Meanwhile, designing potion labels brings in art.
For an engineering challenge, ask your child to plan how they will catch the overflow. Which tray should they choose, and where should they place the cup?
In addition, the activity encourages children to ask questions, make predictions, and test ideas.
Finally, remember that an unexpected result can lead to another discovery. If the brew doesn’t rise as high as expected, ask: “What could we try differently next time?”
Keep the Creativity Going with Camp STEAM Canada
A little fizz can lead to a lot of curiosity!
At Camp STEAM Canada, hands-on activities invite campers to explore, create, and solve problems while having fun.
Registration opens November 2, 2026! Check campsteam.ca for details and start planning your camper’s next adventure.
Witch’s Brew Ingredients and Supplies
For one batch:
- 1 tablespoon baking soda
- ¼ cup white vinegar
- 1 teaspoon liquid dish soap
- 1 tablespoon water
- A few drops of food colouring (optional)
You’ll also need:
- A small plastic cup or open container
- A deep tray or baking dish
- Measuring spoons and a measuring cup
- A spoon for stirring
- Paper and colouring supplies for a potion label (optional)
- A ruler for comparing foam heights (optional)
Parent tip: Supervise the activity, keep the mixture away from mouths and eyes, and protect surfaces from food-colouring stains. Always leave the container open so the gas can escape.