Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Steel Wool, Soap, Water Absorption


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

Question:
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?

Replies:
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


Click here to return to the Chemistry Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory