If you’re looking for some good clean fun, this classic expanding Ivory soap activity won’t disappoint. Curious little scientists will be amazed as a bar of Ivory soap grows in a matter of seconds. So stock up on those Ivory soap bars because your kiddos will be begging to see this magic growing soap more than once!
The prep for this demo couldn’t be easier. All we needed was a bar (or two, or three…) of Ivory soap, a microwave, and a microwavable bowl or plate.
Don’t try substituting a different brand of soap. Ivory soap is whipped with air and that’s the key to this experiment working.
Magic Expanding Soap
Before zapping the Ivory soap, I had my kids examine the bar. They noticed the wrapper felt a little damp and the bar felt slightly moist.
I had bought an 8 pack of soap so we used one bar to see what would happen if we placed the bar in a bowl of water. It floated!
I didn’t explain why the soap floated yet – I wanted to let my kiddos try to solve that mystery later.
Now we were ready for the real show!
I put the Ivory soap in a microwaveable safe bowl and placed it in the microwave for 2 minutes. After 15 seconds or so the soap began to grow.
My 7 year old literally jumped up and down with excitement yelling, “the air is getting hot and expanding” over and over.
I was cracking up that she was so excited by this simple demonstration and managing to explain it with all that enthusiasm at the same time. That was one of the best reactions yet during all of our many science experiments.
After about 2 minutes on high, the soap stopped expanding.
We carefully removed the bowl from the microwave and let the soap cool for a minute or so before I allowed the kiddos to explore it.
Both kids could barely wait till the soap cooled before grabbing a chunk to explore.
They loved squeezing the fluff and crumbling it between their fingers. It felt foamy but dry and easily broke apart into powder.
After giddily crumbling 2 bars of soap back into the bowl, my 4 year old ran to the kitchen for a glass of water and added it to the soap to try to make the soap back into a bar again. Wow! What an amazingly messy sensory experience. My kids couldn’t get enough, so into the microwave went another 4 bars of soap!
The Science Behind the Expanding Soap
Ivory soap is whipped with air when it’s made. Those tiny air bubbles also contain water molecules. When these air bubbles and the water within are heated in the microwave, the water vaporizes, changing from a liquid to gas.
According the Charles’s Law, as the temperature of a gas increases, the volume of the gas increases too.
This expanding of the gases (both the air and water contained inside the soap) causes the soap to expand and become fluffy. The heat also makes the cloud-like soap to be soft and pliable.
Super Cool Science Kit
Continue the fun with our Super Cool Science Kit – 30 of our favorite kid-friendly experiments and a no prep science journal little scientists can use to record their results!