What’s the process that makes it good at something so far off from its composition?
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To put it simply, things that are oily will dissolve in oily substance (meaning they are non-polar). The other stuff tends to dissolved in water, like salt for example (this is a polar solvent. What soap does is take an oily like molecule, attach to that a part that dissolves in water and you have soap. When washing clothes for example, say with an oily stain, the oily part of the soap molecule will help dissolve, or clean, the stain. But the washer uses water right? That is polar, so you need to get the oily material off the clothes into the water somehow and wash it away. Well the oily part of the soap has already dissolved the oily stain, now those soap molecules will form a “liquid” soap bubble around the oily substance. Remember one side of the soap molecule is oily, they will all point in towards the dissolved oil, with the other side pointing out, so you end up with tiny spheres of soap molecules surrounding the oily stain material. Inside that sphere is the oily tails of the soap and dissolved oily stain, on the surface of that sphere are the part of the soap molecule that dissolves in water. Now you have these tiny spheres that can be suspended in water because that little sphere on the surface has polar water dissolving part of the soap, inside has the oily tails of the soap in a little sphere that can float around in the water. Wash all that water away with all these little spheres in them washes away the oily stain along with the soap that surrounds it, now you have clean clothes. This same general principle works when using soap on other things while washing with water too.
I am a chemist working for a big soap manufacturer. Let me try to explain.
I will call oil and fat only fat in the future, because chemically they are not so different.
Fats like fats oils and water likes water, this is why they don’t mix.
In the process of soap making a part of the fat molecule is changed to like water. This means that the molecule is no longer a fat, that likes fat, but a new molecule, called a surfactant that has a part that likes fat and a part that likes water.
This new molecule likes to be on the surface where water and and oil touch.
When the concentration of surfactant gets high enough the part where the oil and water touch gets saturated. For these molecules to still touch both water and fat either the fat or the water needs to broken up in tiny balls so more of these surfactants fit on the area where fat and water touch.
These tiny balls of fat can easily be washed away in an access of water.
We call it saponification! Which basically means taking oils and mixing them with strongly alkaline stuff, like wood ash left when wood completely burns away, which turns the whole thing into a chemical that mixes both with water, and with other oils, letting them dissolve in each other.
making soap is actually a really fun and easily accessible craft. Anyone with a kitchen and some patience can make cold-process soap.
Water is great at dissolving watery things, but its molecules repels oil.
Oil is great at dissolving oily things, but its molecules repels water.
*What if* you could make a special molecule that had two sides: one side that can bind with water, and the other side that can bind with oil?
Congratulations! You have now invented a *detergent*. It can bind with oil *and* dissolve with water.
Imagine each soap molecule as a string. The string itself LOVES Fat and the tip of the string LOVES water. The string is just one molecule so despite the difference they stay together. The effect is the string grabs on to fat and the tip latches it on to the water.
This allows you to essentially glue fats to water making cleaning with water and soap actually effective against fats and oils.
I have a question extending from this: if soaps aren’t antibacterial, how do they clean/get rid of things like salmonella? I understand it removes debris and things that carry salmonella etc, but how can it remove it to the point where it’s gone and not an issue? Wouldn’t it stultifying just stick around?
The oil on your skin doesn’t bind with water very well, so just rinsing with water doesn’t remove much.
But soap is good at binding with both oil and water, so the soap molecule binds with the oil on your skin, and when you rinse off it binds with water molecules and gets pulled off your skin.
We all know water doesn’t mix with oil. But oils mixs with other oils.
Soap is basically half water and half oil. The oil mixs together and the water mixs together, so when you shower, the water mixs with the water side and takes the oils with it and other oils on your skin with it.
———-(insert fats/oils)———-0000
* the ‘———-‘ represents train cars that want to pick up date and oil
* the (0000) is the train pulling the fats/oils train cars, (0000) does not like fats/oil. It wants to pull them away from where they are deposited.
* this is how soap/surfactants work
* soap/surfactants are made from fat and oils but are chemically different through a process called saponification.
A fat is fatty acid molecules held together with a glycerol bond. Point a couple fingers up, the fingers are the fatty acids, and your knuckles are the bond. Making soap breaks this bond, stripping off the glycerol, leaving you with a bunch of fatty acid salts (individual fingers floating around, sans knuckles). Because that bond isn’t there anymore, one end of the fatty acid salt, or “soap,” molecule still likes fat, but the other end now likes water.
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