| MadSci Network: Chemistry |
Sorry that it has taken me so long to respond. The pepper "particles" all stay together, or nearly so, because they do not interact well with water molecules. Water molecules are polar and the surface of the pepper "particles" is non-polar. The water molecules tend to "push" the pepper together, so that there will not be so many of the water molecules on the surface that must interact with the pepper. The water molecules have a special attraction for one another on the surface; this attraction accounts for the surface tension that lets some insects "walk" on the surface of the water and that lets us "float" some heavier than water objects (like a paper clip) on the surface of the water.
Soap or detergent act as a surfactant or surface-active agent. When we add a surfactant to the water, the surfactant molecules disrupt the special attraction; they get between the water molecules. This breaks down the surface tension AND would allow the pepper flakes to be free of one another. The intrusion of the surfactant molecules at the surface between the water molecules will push the pepper around.
I hope that this has answered your question. Sorry for the delay.
Dr. Jerry Franzen Chemistry Department Thomas More College 606-344-3377 franzenj@thomasmore.edu
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