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Liquid, solid or powder, all soaps work similarly
Soap is so easily available nowadays that we often take it for granted. Though soap became commonly used around 1000 years ago, it took a long time for people to realize just how useful it is! Disease was mysterious for a long time. Nobody knew how diseases like cholera, malaria, or smallpox spread. Theories included “bad air” or internal imbalances of “humors.” An Austrian doctor named Semmelweis was the first to realize that using soap reduced mortality of mothers after giving birth. Can you believe this discovery only came in 1847?
Bacteria and viruses are killed by soap, so washing your hands well is key to avoiding falling ill.
The Chemistry of soap
Soap requires two main ingredients: fat and an alkali. An alkali is a water-soluble chemical with a pH above 7. A fat is a molecule rich in carbon and hydrogens. Unlike alkalis, fats never dissolve in water.
When these two substances combine, they do something very special! They form a molecule which has a very special property. It both is and is not soluble! How can this be?
The soap molecule has a head and a tail. The head is hydrophilic, or water-loving. The tail is
hydrophobic, and avoids water.
How does soap work?
When a simultaneously water-loving and water-avoiding substance is put into water, a very interesting thing happens. All the hydrophobic tails move towards each other. Since the heads are large, either a bilayer can form, or a ball can form.
If you’ve ever tried to wash grease off your hands without soap, you might have noticed it is nearly impossible. This is because grease is hydrophobic, and will not bond with water and be washed away. When soap is used, the hydrophobic tails are attracted to the grease. Fat gets pushed into the middle of a soap molecule ball. Since the heads are water loving, the whole ball can get washed off!
Bacteria and viruses have a layer of fats around them. When these fats are broken down, the bacteria and viruses die. This is how soap works against disease, and against stains and fats!
Glossary
Alkali: A water soluble substance with a pH above 7
Hydrophilic: Water-loving
Hydrophobic: Water-avoiding
pH: a measure of whether a substance is acidic or basic. A low pH means something is acidic, like lemon juice; pure water has a pH of 7 and is neutral; a high pH means a substance is basic, like soap or bleach
Flesch Kincaid Grade Level: 60.6
Flesch Kincaid Reading Ease: 7.4
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