MadSci Network: Chemistry

Re: Why does a soap and water mixture explode when you put it in the microwave?

Date: Mon Nov 8 19:21:55 1999
Posted By: Edward Peterson, Staff, Chemical Engineering, S&B Engineers and Constructors
Area of science: Chemistry
ID: 941994386.Ch

Dear Mr. Lauren,

If you have time, I would like you to tell me who gave you the idea of 
putting soap and water together in a bowl and putting it in the microwave 
oven.  I have done similar things and I hate cleaning up the mess!

I would really like to have more information, if you don't mind.

If the soap was liquid soap and water, I would be surprised if the mixture 
would burst out of the bowl.

If the soap and water mixture was thick, like a paste, then I can see why 
it might happen.

In a microwave oven, the energy goes inside an object a few centimeters 
before it is converted to heat.  That means the inside of a pasty mixture 
would boil before the outside would be hot.  If the inside is boiling and 
building up pressure while the outside is hard, when the pressure gets 
large enough to break out, it explodes like a bomb.

You can do the same thing with a fresh egg, but I must warn you that the 
result really, really stinks.

Get permission from an adult before doing any experiments, and best of 
all, have them watch with you.

Dr. Peterson

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