|MadSci Network: Chemistry
Before we look at how shampoos and liquid soaps are made lets just look at the difference between them, as they contain totally different chemicals and are made by different methods. Liquid Soap is just a thick water solution of normal soap, just like you find in any bar of soap. The liquid soap may or may not contain other ingredients such as :preservatives, colours and fragrances. So how is liquid soap, or any soap for that matter made. All soap comes from the reaction of fat and sodium hydroxide. Just about any type of natural (animal or vegetable) fat or oil can be used and as the picture below shows the reaction of 3 molecules of NaOH with one fat molecule generates 3 molecules of soap and 1 molecule of glycerol. Soaps have been in use since 600BC but their main disadvantage are that they are quite harsh, they are often very basic and react easily with metal ions found in most water to form insoluble scums. In recent years chemists designed detergents that act in exactly the same way as soap does but are much less harsh and do not form the insoluble salts that soaps do. Detergents are not made from fats such as animal fat like soaps are but are made from the petroleum industry. The reactions are quite complicated but involve the reaction of molecules of sulfer trioxide or sulfuric acid on petrolium to form detergents like the one show below. Most cleaning products these days use detergents instead of soap as their cleaning agent due to its more desirable properties. Infact many products that call themselves as soaps, especially for cleaning skin and faces contain detergents as well as soaps. Most shampoos are a mixture of many detergents as well as colours and fragrances. Detergents are used in shampoos as soaps are considered too harsh for hair. There are many sites on internet dealing with the hobby of making soaps you can find a good selection of sites on soap making and detergents in general at: Yahoo.com The Soap and Detergent Association David Barker
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