Because soap is a salt, it partially separates into its component ions in water. The active ion of the soap molecule is the RCOO-. The two ends of this ion behave in different fashions. The carboxylate end (-COO-)is hydrophilic (water-loving), and is said to be the head"" of the ion.The hydrocarbon portion is lipophilic (oil-loving) and is called the
tail of the molecule. This unusual molecular structure is responsible
for the unique surface and solubility characteristics of soaps and other
surfactants (agents affecting the surface of a material).
mixture of soap and water, soap molecules are uniformly dispersed. This
system is not a true solution , however, because the hydrocarbon
portions of the soap's ions are attracted to each other and form
spherical aggregates known as micelles. The molecules tails that are
incompatible with water are in the interior of these micelles, while the
hydrophilic heads remain on the outside to interact with water. When
oil is added to this system, it is taken into these micelles as tiny
particles. Then it can be rinsed away.