2014-02-15 by seoer8Soaps are salts of fatty acids of the Metal soap general, daily soaps of fatty acids having a carbon number of generally from 10 to 18 , a metal mainly alkali metal such as sodium or potassium , and is also useful for some organic bases such as ammonia, ethanolamine , triethanolamine and the like made of special purpose soap . Soap, laundry soap , toilet soap , metal soaps , liquid soaps , as well as related products of fatty acids , hydrogenated oil , glycerin. Soap, salts of higher fatty acids containing , in addition , also contains a rosin , sodium silicate , perfumes, dyes and the like filler. From a structural point of view, the non- polar hydrophobic portion comprising ( hydrocarbon ) and a polar hydrophilic portion ( carboxyl group) in the molecule of higher fatty sodium . Hydrophobic group has lipophilic properties . When washing, the oil stain is agitated , dispersed into small droplets after contact with soap , sodium higher fatty hydrophobic molecule ( hydrocarbon ) is inserted in the droplets , by the van der Waals force and oil molecules together . Easily soluble in water, the hydrophilic group ( carboxyl ) partially stretched out droplets into the water . Thus the droplets are surrounded by soap molecules together , dispersed and suspended in water to form an emulsion , and then the friction vibration , the rinsed away with water , which is the principle of the soap detergent . But ordinary soap should not be used in hard water or acidic water. In hard water because of the formation of sparingly water-soluble calcium and magnesium stearate , acidic water is generated in the water-insoluble fatty acids, greatly reducing its cleaning ability .