Tristearin (a crystallizable triglyceride made up of 3 stearic acid molecules and one glycerol molecule) is extracted from tallow, a mixture of fats obtained from cow fat. When this tristearin is heated with sodium hydroxide, sodium stearate is formed. Sodium stearate, or the soap molecule, is composed of sodium (an alkali, or soluble salt of an alkali metal) and stearate (a fatty acid). This soap molecule has two very distinct ends – a long hydrocarbon “tail” and a carboxyl acid “head”. The “tail” of this molecule is hydrophobic, or water-hating, whereas the “head” of this molecule is hydrophilic, or water-loving.

As a result, when this soap molecule is added to water containing dirt (ex. During washing hands), the hydrophobic “tail” tries to avoid contact with water by attaching itself with oil/grease, while simultaneously, the hydrophilic “head” attaches to water molecules. Consequently, the soap molecules act as a bridge between water and oil and rinse away the grease and dirt with the water. (When water alone tries to rinse away grease, it doesn’t work because grease is hydrophobic. However, through this method, the soap molecule is successfully able to trap the grease/dirt while at the same time staying in contact with water).