Soap is an anionic surfactant. Surfactants, also known as surface active agents, decreases the surface tension of water, allowing it to spread and wet surfaces.
They are water-soluble sodium or potassium salts of fatty acids. Soaps are made from fats and oils, or their fatty acids, by treating them chemically with a strong alkali.
Fatty acids are the components of fats and oils that are used in making soap. They are weak acids composed of two parts: a carboxylic acid group consisting of one hydrogen (H) atom, two oxygen (O) atoms, and one carbon (C) atom, plus a hydrocarbon chain attached to the carboxylic acid group. In most cases, it is made up of a long straight chain of carbon (C) atoms each carrying two hydrogen (H) atoms.
The term alkali describes a substance that chemically is a base (the opposite of an acid) and that reacts with and neutralizes an acid. The common alkalis used in soap-making are sodium hydroxide (NaOH), also called caustic soda; and potassium hydroxide (KOH)