Erupting Soap is a super fun and easy science experiment for your kids! Using just a bar of Ivory soap and your microwave, you and your kids can have a quick and easy science experiment that will delight everyone. Use this simple science activity for kids at home or in the classroom.
How to make Erupting Soap in Microwave
Kids of all ages will think this science experiment is cool! You are going to love what happens to a bar of Ivory soap when you put it in the microwave.
Related: Baking soda and vinegar eruptions
I first asked my son what he thought might happen if we put a bar of soap in the microwave. He naturally said that it would melt. Most soaps will melt, but Ivory soap is different because of the way it is formed.
More on that later…
*Adult supervision is needed for this science experiment.*
Ivory Soap Experiment – Ingredients Needed
- A bar of Ivory soap (no substitutions allowed)
- A microwave safe plate
- A microwave
Yep, that’s it!
Video: microwaving ivory soap
Instructions on Ivory Soap Science Experiment
Step 1
Put your bar of Ivory soap on the microwave-safe plate and microwave it for 2 minutes.
The action starts right away as the soap quickly starts to grow.
Step 2
When it stops growing you can stop the microwave, although it won’t harm anything if it runs for the full 2 minutes. The soap just won’t grow any bigger at that point.
My son was absolutely giddy watching this for the first time…and every time after that. I must admit I haven’t gotten tired of watching erupting soap either!
Finished Ivory Soap Eruption
When the soap had finished erupting, this is what we got.
Why does this Microwave Soap Erupt?
There is a scientific principle called Charles’ Law which states that the volume of a gas directly increases with an increase in temperature. So the hotter air gets, the more space it wants to take up, and the more pressure it will produce in order to take up that space.
Ivory soap is an unusual kind of soap, in that it has a lot of air pockets in it.
There is also a lot of moisture in Ivory soap. When it is heated, the soap softens but before it gets close to melting, the moisture in the bar gets hot and turns to gas (steam). Add that to the already present air particles throughout the bar and you’ve got a lot of steam trying to get out. As the steam pushes its way out, it expands the soap.
Charles & Gay-Lussac’s Law
Here’s a simple animation of Charles’ Law to help explain how volume and temperature are directly related. Other soaps are not as porous as Ivory soap because they do not have air pockets throughout. Therefore, the steam isn’t able to build up inside it and instead the soap just melts.
Except for the loss of water, this is still Ivory soap. No real chemical change took place. The soap is puffed full of air so we had fun crumbling it up, and then we whisked in a bit of water and made “soap paint”.
Crumbling Ivory Soap
We painted on styrofoam trays both with paintbrushes, and with our hands.
Once the “Wow Factor” died down just a little, we decided to get a little more scientific so we pulled out a scale.
Related: Things to make with soap
Does Ivory Soap Get Lighter after Being Heated?
We weighed a whole bar of ivory soap before and after the eruption experiment to see if it got heavier or lighter after heating it up.
The weight of a bar of Ivory soap:
- Ivory soap bar weight before experiment: 78 grams
- Ivory soap bar weight after the experiment: 69 grams
The erupted bar weighed less due to moisture evaporation.
Other Observations from Ivory Soap in Microwave
1. The soap has expanded six or more times its original size, but actually weighs less now because of water that has evaporated. Amazing!
2. If you microwave half a bar of Ivory soap, the cut side of the bar will expand significantly more quickly and with more force than the uncut side. In this experiment above, the force of the expansion out of the cut side was so strong that it flipped the bar from its side to an upright position so that the eruption from the cut side was then facing upward.
3. The plate was hot all over after a minute and half. However, the plate was significantly hotter directly under the expanded soap. Microwaves focus on heating water molecules, so the water in the soap heated quickly and made that part of the plate hotter.
Ivory Soap Microwave FAQs
“Ivory Gentle Bar Soap gives you a safe, pure clean trusted for generations. Our simple soap is free of dyes and heavy perfumes, is dermatologist tested, and continues to be so pure, it floats! …Dermatologist Tested, Free of dyes & heavy perfumes…99.44% Pure.”
-Ivory Soap website(Gentle Bar Soap, Original Scent)
When you ask if it is safe to microwave Ivory soap, the answer will be no because of the dangerous chemicals. We can not find any dangerous chemicals. So, please understand that some think this is dangerous, but have not given us the reason why.
2 minutes is the recommendation for the amount of time to let Ivory soap stay in the microwave.
Once your Ivory soap cools, you can play with it.
Active Time
2 minutes
Total Time
2 minutes
Difficulty
Medium
Estimated Cost
$1
Materials
- 1 bar of Ivory soap (no substitutions allowed)
- microwave safe plate
Instructions
- Remove the wrapping from your bar of Ivory soap.
- Set your Ivory soap bar on a microwave safe plate in the microwave.
- Set on high for 2 minutes in the microwave.
- Watch what happens.
- Let cool before touching the Ivory soap.
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Did you know? We wrote a science book!
Our book, The 101 Coolest Simple Science Experiments, features tons of awesome activities just like this one that will keep your kids engaged while they learn. How awesome is that?!
More Science Fun from Kids Activities Blog
Hope you enjoyed making a bar of soap erupt in the microwave! Tell us your kid’s reaction in the comments!
