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The Wonders of Soap and Detergent. How do they Work?

The powerful doings of science that help keep things clean!

How is it that whenever you place your dirty clothes in the laundry, they come out clean? Or when you wash the dishes, they always come out looking sparkling new? Well you may have answered your question by saying that you just add that viscous liquid or powder that causes water to foam. You know, they come in different colors: reds, blues, purples, white, I mean the colors are endless and you just refer to it as “soap.” Well, have you ever wondered how soap actually works? We all take it for granted because we use it every single day, but have you ever sat down and really thought about why does it do that? What is the science behind it? I hope that this blog post will answer all those questions and more as we delve into the science of soaps and detergents!

First off, remember the word “surfactant”

The word surfactant is a chemical compound that is a part of the detergents and soaps that you use and is what allows for its cleaning properties. We can all give our thanks to chemistry for this as it is due to the properties of the compound that causes it to remove oil and grease. So, how does it work? Well, a surfactant is made up of organic compounds that are amphiphilic, which means that it has both a hydrophobic and hydrophilic component to it.

The hydrophobic portion of the compound is the side that does not like water so it is not dissolvable in polar compounds such as water. Hydrophilic compounds dissolve in water because they are polar, just like water is. Therefore, surfactants having a hydrophilic side allow the soap and detergents to be soluble in water.

What does the hydrophobic side do?

Good question! Since the hydrophobic side is not water soluble, can you think of anything else that may not be water soluble (aka not able to dissolve in water)? Well oils and greases, which are the most common forms of mess that needs to be cleaned, are hydrophobic. Basic science says that “like dissolves like” which means that substances that are similar will mix together. In essence, the hydrophobic side of the surfactant is what allows for the oils and greases to be soluble in the water. The chemical detergent actually adsorbs onto the surface of whatever you’re washing (clothes, dishes, etc.) where the oil and water meet and the hydrophobic portion of the surfactant pulls the oil off of the surface. And since the surfactant also has a hydrophilic side, the solution is able to be soluble in water. Multiple hydrophobic sides attach to the grease with the hydrophilic side face outwards. A combination of multiple surfactants is called a “micelle.” This traps the oil in the surfactant complex and is what prevents the oil from attaching back on your clothes and/or dishes.

Ahh, the beauties of science.