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  • Writer's pictureRBG Janitorial

How soap works

In the hope that I'm not the only one who finds this fascinating...

Soil or Oil - cleaning is all about chemistry

Dust, dirt, grime – everything you will ever want to clean is either soil or oil. The organic particles of dust and debris float through the air and gather in crevices. Oil, grease, and fats bind these particles to surfaces, making them dirty.

Dust is easily removed from a surface. If you’ve ever tried to rinse a greasy pan with plain cold water, though, you know how helpful soap can be. But how does soap work?

Water doesn’t always clean well by itself. As the saying goes, “water and oil don’t mix.” The reason for this is a property of water called surface tension.

Surface tension is created by water molecules drawing together to form the smallest possible surface area. It's what makes water fall in droplets rather than a stream. When a liquid is exposed to air, surface tension creates an elastic veneer. If you pour water onto an oily surface, the water will just skid across the top of the oil. It’s the same at a microscopic level when using a damp cloth to wipe grime. Surface tension makes it difficult to get into and under the oil in order to remove it.

One way to reduce surface tension is to heat the liquid. As temperature decreases, surface tension increases. If the liquid is cold enough, it becomes solid (ice). Heat agitates molecules so that they are less likely to bond, which decreases the surface elasticity. This is why hot water has been traditionally used for cleaning.

Saponification is the chemical process of creating soap from lye and fats or oils.

Lowering surface tension is what makes it possible to use water to lift grime. A substance that reduces surface tension is called a surfactant, short for “surface acting agent”. As a surfactant, soap is unique because of its behavior toward oil and water.

Each molecule of soap has two ends. One is hydrophilic, meaning it “loves” water, and one is hydrophobic, meaning it “fears” water. Simply put, one end of every soap molecule is drawn to water, while the other end draws away from water.

When added to water, the hydrophobic ends of soap molecules draw inward, away from the water. The hydrophilic ends are forced outward, attracted to the water. This forms what is called “micelles” in chemistry – more commonly known as soap bubbles.

Oils, fats, and other alkaline or greasy substances are all hydrophobic. Soap will draw these together into the center of the micelles. The hydrophilic ends of soap will encapsulate the oily particles with water, and the oil molecules become trapped inside this molecular structure. It is then possible to remove and discard the dirty water.

True soap is a combination of fatty acids and lye. Its sole function is to act as a surfactant. Modern "soaps" are actually detergents that use chemical surfactants. Detergents also contain other ingredients to provide added benefits - but that's another article for another time.

RBG Janitorial is a local, woman-owned small business providing first-class commercial cleaning services in Illinois, Wisconsin, and Iowa. For more information, contact us here.


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