Soap feels slippery, it cleans fatty goo, it’s kinda weird. When you drop a bottle of corn oil, after screaming and cursing, you reach for Dawn. But why? Because that’s what your mom taught you to do… but, like everything else, there’s science behind the household wisdom. And it’s rather basic.
Zooming in On the Molecules
The atoms that make up all of the substances around us have smaller particles inside them.
Those Subatomic Particles Are:
- Neutral neurons in the center of the atom,
- Positive protons (also in the middle),
- And negative electrons (spinning in a cloud around the center).
Some atoms are hell bent on hanging on to those electrons, especially if they don’t have enough of them to feel stable. Other atoms have too many electrons. When we measure how willing atoms are to pass out or grab electrons, that number is called pH.
Bases have a high pH. They carry a lot of electron baggage, which creates areas of the molecule that are quite negative. That negative charge means that they will attack molecules with positive attitudes and bust them apart. It’s awful, really, if you think about it.
But Why Do Bases Feel Slippery?
The cells in your body are like little balloons filled with water, busy little structures called organelles, DNA, and the other molecular machinery that keeps you alive. But unlike balloons, these cells (including the ones in your skin) are made of fatty membranes instead of rubber. Those fats are made of molecules that have both a positive end and a negative end. Now we can use all of this information to put together an answer:
- Fats have positive parts.
- Soaps have basic bits.
- Your fingers are covered with skin made of cells with fatty membranes
- Your fingers are also coated in a little body oil.
- The negative side of the basic soap breaks down the positive end of fats.
- The fats turn into salts and glycerol.
Glycerol is a sugar alcohol, the white powdery solid they use to make artificial sweeteners. As you know, salt and sugar dissolve easily in water and… voila! A thin layer of fat from your skin is literally dissolving in the water while you wash.
Going back to the veggie oil – taking a wet washcloth to the oil will schmear it around and do nothing. Water is super-stable with no negative or positive charge. The oil won’t break down itself or the water, but just blobs up into scared little balls. Oil and water don’t mix. But once you add that soap, and your puddle is reduced to soluble sugar and salt, you can wipe up the disaster with ease.
But still, the slippery feeling…?
You know that when you rub something against sandpaper it creates friction. The same thing happens at the molecular level to everything. Even in a seemingly smooth liquid, the tiny molecules constantly brush up against all the other particles around them. Depending on their size, shape, and how those molecules react with each other, they either slip right on by or things get rough.
- Liquids that rub each other the wrong way don’t flow as easily (molasses).
- If it’s smooth sailing, they appear thin and fast to us (water).
- This is referred to as the fluid’s viscosity, although we usually think of it as “thickness”.
The thick fats in your skin break down to salts and sugars that dissolve in the water. Water already slides around pretty well, but the sugars, in particular, make it even smoother. There is so very little friction when glycerol and water meet, that it feels all smooth and slick and your fingers slide right over each other.