 In this video, we are going to learn about how soap is made by a process called hydrolysis, and how we can control whether the soap produced is hard or soft. Soap is a detergent and has been around for thousands of years. Traditionally, ash from wood fires acted on animal fat and the first soap making processes. When animals were baked on a spit over wood fire, the fat will drop onto the ashes. The ash contained potassium carbonate which broke apart the fats and so the ashes were wetted were excellent as a cleaning agent for the pots and pans. Soap is a substance that, when used with water, removes dirt and oil away from the skin or other materials such as clothing. Soaps have always been made in a similar way, using hydrolysis. The fancy word for this process is saponification. Chemically, fatty acids or oils combine with a base, typically, soared in hydroxide and water. The result of this process is soap and a chemical called glycerine. This is seen in the chemical reaction where the fatty ester highlighted is broken down to form a carboxylate salt and glycerin. Glycerin is found in luxury soaps because of its ability to make soaps appear translucent. There are two kinds of soap, hard soap and soft soap. What do you think this means? Pause the video and continue when ready. Soaps can be hard meaning they can be moulded into shapes, typically a bar, or they can be soft like those found in hand washes which are liquefied and kept in bottles. In addition, hard soaps dissolve more slowly whereas soft soaps dissolve more quickly. Hard soaps are made by using certain fats like coconut oils, lard or cocoa butter. Look at the equation shown now. The R group represents the size of a hydrocarbon chain. How do you think this might influence whether a soap is hard or soft? Pause the video and resume when ready. The R groups of a particular length alters the fat's properties, particularly its melting point and its solubility. In addition, the choice of base, such as whether you use sodium hydroxide or potassium hydroxide is also important. Typically, hard soaps are made when fatty acid esters with R groups containing 12 carbons or more use sodium hydroxide in the saponification process. Fatty acid esters with 6 carbons or less are not used as they irritate the skin and smell pretty funny. Soft soaps use fatty acid esters like avocado oil, sunflower oil and castor oil to name a few and are reacted with potassium hydroxide when saponified. In summary, soaps are made by a process called saponification. Really, this is a hydrolysis reaction whereby a fatty acid ester bond is broken and a carboxylate salt and glycerin are formed. That carboxylate salt is the soap that we use when we wash and can be hard as in a bar of soap or soft like that found in a hand wash.