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Most kids love taking baths and enjoy it even more when there’s something different involved (bubbles, paint, new toys). I’ve got a fun addition to bathtime that doubles as a STEM lesson!
This experiment allows children to learn about chemical reactions, measurement, and color blending while making their own bath bombs.
This is a super simple mixture that takes no time at all but is really fun to use!
How to make the DIY Bath Bombs STEM experiment
Supplies you will need
For this experiment, you’ll need:
- Silicone cupcake molds
- Baking soda (1 cup)
- Corn starch (0.5 cup)
- Citric acid (0.5 cup)
- Epsom salt (0.5 cup)
- Water (3 tsp)
- Whisk
- Essential oils
- Olive or avocado oil (2.5 tsp)
- Large bowl
- Small bowl (that you can easily pour from)
- Food coloring (optional)
Before you start
If you want to use food coloring to dye your bath bombs, I would suggest adding drops of food coloring into your wet ingredients (step 1) before mixing the wet and dry ingredients. If you add the food dye later, it’s very challenging to mix!
Instructions
Here is how to do this experiment with your child:
Step 1: Make the dry and wet ingredients in separate bowls
In a bowl, combine the dry ingredients. Using a whisk, mix up the dry ingredients to ensure there are no clumps and that it’s all well-mixed.
In a separate bowl that you can easily pour from, stir together the wet ingredients.
Step 2: Combine the wet and dry ingredients (slowly!)
Slowly start to pour the wet ingredients into the bowl with the dry ingredients. Pour only a little bit at a time and whisk to mix completely. You may be adding liquid too quickly if you see the dry mixture fizzing, so pour as slowly as you can.
It will not look very wet, even after you have poured all of the wet ingredients into the bowl. That’s okay! It should still look powdery even after the wet ingredients have been added.
Step 3: Test out the mixture
After you have whisked together the wet and dry ingredients, grab a handful and squeeze it. If it forms together in big chunks, it’s the right consistency. If it’s still too powdery to form together, add a tiny bit of water to the mixture, use the whisk to mix it thoroughly, and test it again.
The first picture below shows the mixture not clumping together very well and the second picture shows it clumping well.
Step 4: Add mixture to silicone cupcake molds
Once the mixture is the right consistency, start adding it to the silicone cupcake molds. Be sure to pack down the mixture into each silicone mold, adding as much or little as you would like into each mold.
Step 5: Allow to fully dry
Wait about an hour or two for the mixture to begin to harden in each silicone mold and then take them out of the molds. We put our bath bombs on a sheet of cardboard to dry.
Leave the bath bombs to dry out overnight and they’re ready to go!
The STEM behind the DIY Bath Bombs STEM experiment
This experiment teaches:
- Chemical reactions
- Color mixing
- Measurement
How it works
When you drop a bath bomb into the water, a fascinating chemical reaction unfolds. The key players are citric acid and sodium bicarbonate (baking soda).
As the bath bomb dissolves, these two substances come into contact with water. This triggers a chemical reaction, where the hydrogen ions from the citric acid react with the bicarbonate ions from the baking soda. This reaction produces carbon dioxide gas, a colorless gas that’s responsible for the fizz and bubbles you see.
The carbon dioxide gas forms tiny bubbles that rise to the surface. This reaction is an example of an acid-base reaction, a fundamental concept in chemistry.
Chemical reactions
When baking soda (sodium bicarbonate) and citric acid are combined with water, they undergo an acid-base reaction. This reaction produces carbon dioxide gas, which is what causes the fun fizzing effect in the bath.
Did you also notice that the water around the bath bomb got slightly colder for a second? That’s because this chemical reaction is known as an endothermic reaction! Heat is being absorbed during the reaction, making the water around the reaction feel slightly cooler.
What are some other examples of an endothermic reaction?
- Photosynthesis: Plants absorb heat energy from sunlight to convert carbon dioxide and water into glucose and oxygen.
- Cooking an egg: The egg absorbs the heat from the skillet (which absorbs heat from the burner) to cook.
- Water evaporation: Heating of water to water vapor.
Color mixing
Adding food coloring to the bath bombs allows children to experiment with color theory and how colors blend.
By combining different food colorings, kids can learn about primary colors (red, blue, and yellow) and how they mix to create secondary colors (orange, green, and purple). They can even get artistic with the bath bombs and add creative designs with the food coloring!
You can also experiment with different color combinations to create different shades and hues, which will give you the opportunity to talk about color saturation.
Measurement
Following a recipe teaches them about measuring ingredients and understanding ratios.
Using measuring spoons and cups, kids learn the importance of accurate measurements in following a recipe.
Adjusting the quantities of ingredients helps them understand the concept of ratios and how they affect the final product.
More experiments about chemical reactions to try out with your child
- Blast Off! A chemical reaction rocket
- Fire vs. Fizz: Using carbon dioxide to extinguish a flame
- Homemade Lava Lamps: Chemistry in action!
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