what is the chemical structure of soap? plz explain?

Answer 1

Soap is usually the sodium salt of a fatty acid such as stearic acid:

CH3(CH2)12COO-Na+

The long hydrocarbon tail dissolves fats, oils, and grease, because it is "like" them. The ionic -COO-Na+ head of the molecule has an affinity for water, so it carries dirt and grime into solution and suspension and "washes them away."

A problem comes when water is "hard," meaning it contains Ca2+ or Mg2+ ions. Salts of soapswith these ions are water-insoluble, resulting in "soap scum" and "ring around the bathtub." The solution is either to soften the water (remove the offending ions) or use a detergent.

It is pretty certain that soap and detergent molecules are structured into micelles in water. A micelle has all the CH3(CH2)16- tails buried inside a sphere, with the -COO-Na+ heads covering the outside of the sphere. That way, all the greasy dirt is buried dissolved inside the micelle, while the surface of -COO-Na+'s render the whole assembly water-soluble. One criticism is that there doesn't seem to be room inside such a sphere to fit all the hydrocarbon tails. But if a micelle doesn't look exactly like that, it's something very similar.