Detergent
Definition and meaning of Detergent in chemistry.
A detergent is a synthetic surfactant that lowers the surface tension of water and emulsifies oils and greases so they can be lifted from a surface and rinsed away.
In more detail
Detergent molecules are amphipathic: each has a hydrophilic (polar or ionic) head and a long hydrophobic hydrocarbon tail. In water, many such molecules self-assemble into micelles, with tails clustered inward around trapped grease and dirt while the charged heads face outward into the water, letting the whole aggregate rinse away. Unlike soaps, which are metal salts of fatty acids made by saponification, synthetic detergents are engineered so their calcium and magnesium salts stay soluble, so they work well even in hard water. Detergents are classified by head-group charge as anionic, cationic, nonionic, or zwitterionic.
Key facts
| Example formula (SDS) | CH3(CH2)11OSO3Na |
|---|---|
| Structure | Amphipathic: hydrophilic head + hydrophobic tail |
| Common classes | Anionic, cationic, nonionic, zwitterionic |
| Field | General Chemistry |
Sodium dodecyl sulfate (SDS), CH3(CH2)11OSO3Na, is an anionic detergent used in shampoos and cleaning products, and in biochemistry to denature proteins for SDS-PAGE electrophoresis.
Frequently asked questions
How is a detergent different from soap?
Soaps are metal salts of fatty acids made by saponifying natural fats and oils; detergents are synthetic surfactants designed so they do not form insoluble scum with the calcium and magnesium ions in hard water.
Why do detergents clean grease from surfaces?
Their nonpolar tails dissolve into grease while their polar heads stay in water, so agitation pulls the grease into water-soluble micelles that rinse away.