The Chemistry of Soap by Tiffany Lee

In order to make doing laundry more efficient on planet Arda, we will stray from the primitive style of washing by beating clothes on rocks over bodies of water to the use of soap. Soap can be used for many purposes apart from the human body. It cleans woolen and other fabrics and is made from renewable resources and is also readily broken down by bacteria after being released into the environment. Soap will not only be great for cleaning clothes, but it is also safe for the environment in Arda as well. Soap is produced by a saponifaction or basic hydrolysis reaction of a fat or oil. The manufacturing soap however is not as easy as rocks and water, but involves a more complex process involving much chemistry. Basically, soap is the alkali salts of a fatty acid, made from the reaction of a fatty acid and the alkali, a strong base that neutralizes the acid of the fatty acids from the fats and oils. The akali can be either sodium hydroxide, known as lye (hard soaps) and caustic soda or potassium hydroxide, known as potash (soft soaps). This soap- making reaction is called saponification, which basically just reacts the fats or oils with caustic alkali. The reaction in saponification, where "R" is some long carbon hydrogen chain is: [RCO]3[C3H5O3](s) + 3 NaOH(aq) -----> 3 RCOONa(aq) + C3H5(OH)3(aq) Another way to produce soap is by basic hydrolysis reaction of a fat or oil. The General overall hydrolysis reaction is: fat+ NaOH --> glycerol + sodium salt of fatty acid This reaction occurs in two steps. The net effect is that the ester bonds are broken and the glycerol turns back into an alcohol. Also, the fatty acid from the fat is turned into a salt because of the presence of the basic solution NaOH. In the carboxyl group, one oxygen now has a negative charge that attracts the positive sodium ion. (Figure 1)

Figure 1- Basic Hydrolysis of a triglyceride The properties of soap are determined by the type of fatty acid and the length of the carbon chain, so for examples: A hard, insoluble soap is made from tallow or animal fats which give sodium stearate (18 carbons). Therefore, fatty acids with even longer chains are even more insoluble. Most of the fats and oils reacted can be found from animal or plant sources, which each has different mixtures of triglycerides molecules, which each posseses three fatty acid molecules attached to one gylcerine molecule. (Figure 2) BACK-HOME-NEXT