Soap and detergents
This topic explores the fascinating world of soaps and how they clean dirt from clothes and food from dishes. This topic should be read in conjunction with the topics Like dissolves like and Talking solutions.
What is dirt?
Like other non-polar molecules such as petrol, wax and grease, most food and dirt is not soluble in water. Soaking greasy plates has little effect!
Why won't water remove grease and
Hence water is not very good at cleaning plates and clothes by itself. What is required is a way of bridging the gap between the non-polar oil (which holds the dirt to the fabric / dishes) and the polar water molecules.
Soap and detergents - bridging the gap
This allows the soap and detergent molecules to bond with both oil and water molecules at the same time, forming a connection between the oil and the surrounding water molecules. Soap and detergents operate at the interface between the oil and the water and are known as "surface active substances".
With enough detergent/soap molecules present and agitation, the oil and dirt will wash off the clothes, attached to the water via the detergent/soap molecules. The agitation is important as detergent/soap molecules stick out of the oil like paddles, which catch the "current" and wash away the oil and dirt with the water.
Soap and detergents
Soap is made by reacting animal fat, stearic acid, with caustic soda,
sodium hydroxide. The chemical name for soap is sodium stearate.
Detergents are made by reacting vegetable oils like lauric acid with
sulfuric acid to produce lauryl sulfate.
Dish washer powders - Warning!
This combination of chemicals makes dish washing powders very efficient, but also very dangerous. Never touch dishwasher powders and keep them away from children. They are strong enough to react with oils in skin and cause damage to eyes. If ingested they will cause severe chemical burns in the throat and can be fatal.
Dry cleaning uses non-water based solvents to clean. Dry cleaning solvents include, hydrocarbons and organochlorines. These are non-polar molecules that are capable of dissolving oils from dirty clothes.