From a chemistry andor physics point of view. How do you explain pepper repelling from dish soap?

by Luther College Photos

Question by Mike: From a chemistry andor physics point of view. How do you explain pepper repelling from dish soap?

You know when you put ground pepper ontop of water in a dish.

The pepper floats on top, covering the water. But when you put some dishwater soap on your finger and stick it in the middle of the dish, The pepper moves away from the finger.

How do you explain this in terms of chemistry and physics?




Best answer:

Answer by ChatNoir
The answer is on this site:
http://www.newton.dep.anl.gov/askasci/gen06/gen06174.htm

The "simple" answer is that the surface tension of the pepper particles is less than "pure" water (about 72 ergs/cm^2), so the pepper particles tend to float on the water's surface. When you add a drop of soap, you greatly reduce the surface tension of the water near the point at which you add the soap. Initially, this causes a repulsion of the pepper particles and the particles tend to follow the high surface tension areas. If you shake the solution, you will find that the pepper particles get "wetted" by the soap solution and the pepper will disperse in the soap solution.

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