Soap chemistry

Soap chemistry

BY : Rhiannon Nevinczenko

The word "chemistry" often invokes images of lab coats, goggles, crazy hair, and beakers full of colorful chemical substances. But chemistry doesn't just stay in the lab; everything is made of chemicals! The word "chemical" can sometimes be used to sound scary, but really just refers to the physical makeup of matter. (More properly, a chemical is a substance with a defined composition.) It may as well be a fancy way of saying "stuff."
So, we interact with chemicals and chemistry every day. For example, you interact with chemistry every time you use soap. Soap is the result of a chemical reaction between different materials - a lye base, fats, oils, and water. The fats (triglycerides) and lye react with one another in a process called saponification. The products are fatty acid metal salts (soap) and a byproduct, glycerol. After this new substance cools and hardens, it is given some weeks to finish the saponification process. Lye by itself is corrosive, caustic, and can cause serious burns. Soap, however, is completely safe. This is the magic of chemistry!
The magic does not stop there. Have you ever wondered how or why soap cleans things? As a fatty acid of a salt, soap has two superpowers: It is an emulsifier and a surfectant. This means it makes a great cleanser and lubricant. At a molecular level, soap has two parts: The first is a hydrophilic (water-loving), negatively charged, polar molecule. The second is a hydrophobic (water-fearing), non-polar hydrocarbon chain. These create micelles (which are like little bubbles) with the hydrophilic end of the molecules out (in the water) and the hydrophobic ends inside. Your skin naturally produces oils, which dirt gets stuck to. When you wash, the dirty oil gets trapped inside of the soap micelles (oil-to-oil inside). These micelles can then easily be rinsed off (they don't get stuck because soap is a lubricant).
If you don't feel like much of a chemist when washing your hands, you can also try making soap. Soap-making recipes and materials are easily found (please follow all safety instructions closely) and can make for a productive, educational home experiment!
Photograph credit: Malene Thyssen and HLHJ via Wikimedia Commons. GNU Free Documentation License.

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