Thursday, October 6, 2011

The Ivory Soap "Explosion"

I absolutely love it when I learn a new science trick.  At this point, I've seen quite a few, and while there are always new-and-improved versions out there, it's not too common for me to come across something brand new.  Which is one of the reasons I love this demonstration (and it's just SO cool).  It's apparently a well-known demonstration, but I've missed it up 'til now.  (And that's another reason why I make a point of sharing the "classic" science experiments that so many have already seen - everyone has to learn about them for the first time, some time). 

On with the demonstration....

Begin with a bar of Ivory soap (or you may want to use a sliver of soap.... you'll see what I mean). 

Make the appropriate observations of the soap. 

Place the soap on a microwave-safe plate. 

Make a hypothesis* about what will happen when the soap is heated in the microwave.

Now heat the soap in the microwave - set the time for 2 minutes, but keep an eye on it (you'll be doing that any way, trust me).

Observe the soap carefullly.

The soap will expand to a huge volume.  If you use whole bar of soap, it will nearly fill the microwave!  Great wow factor! 

It deflated a little at this point, because my camera's batteries died at this point and I had to wait for them to recharge.

Why does this happen....
Remember when the Ivory floated because it had more air in it than the "other" soap?  When the Ivory is heated, the soap softens and the air bubbles expand.

How can you use this in your science class?
  1. A follow-up to the previously mentioned density experiment.
  2. A discussion of gas laws (Charles Law, specifically) - when a gas is heated, its volume will increase. 
  3. A lesson on physical and chemical changes.  Explosions are chemical changes by definition.  This demonstration looks like explosion, but it's not.  It's just a physical change. 

*A funny story - I told my 5 year old that we were going to do a science experiment after dinner.  He asked what we were going to do and all I would tell him is that we were using soap.  Then I asked if he had any hypotheses about what would happen to the soap (knowing absolutely nothing about what we were going to do to it) and he said "It's going to explode."  I think he was a little surprised at how close to right he was!


  1. I have seen this experiment done in a few places looks like fun! It almost makes me wish we still had our microwave, but not quite ;) I bet the boys LOVED it!!

  2. A science lesson and an opportunity to clean your microwave :).

  3. We had a discussion in class today about whether this was a chemical change or a physical change. Some students thought it was physical because, it was still soap because it foamed up when wet and that the reason it expanded is the moisture changing from liquid to gas. The color and smell stayed the same, also. Some said it was a chemical change because of the energy from the microwave caused the soap to react with the heat and expand. What are your thoughts?

    1. Great discussion question! Physical change because it's still soap; no reaction took place. Just because there's energy involved doesn't mean it's a chemical change.