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Name: Casey Status: student Grade: 4-5 Location: FL Country: USA Date: Spring 2012

I have two steel wool pads. One I rub with soap the other not. The one with soap absorbed the water but did not rust. The wool with no soap did not absorb the water but it rusted on the outside. My question. Why do the one with soap absorb the water?

That is what soap does most, Casey. It is a wetting agent. One end of the soap molecule likes water. The other end likes other things more. So when there is soap in the water, it makes water wet the surfaces of various solids easier. And when water wets all the way around the surface of one steel fiber on the outside of the pad, then it has penetrated a little farther into the pad. That lets more water into the space between the fibers, bringing more dissolved soap with it, which helps wet more fibers. The water goes all the way in quicker than it would without soap.

I am surprised the steel wool pad with soap did not rust in your experiment. Soap doesn't usually protect surfaces much. But, rust occasionally makes weird choices of when to start, so I am not too surprised.

Jim Swenson

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