What’s the process that makes it good at something so far off from its composition?
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Precisely *by* being made of fats and oils.
Water is what is called a polar molecule. This basically means there’s one end that is much more negatively charged and another end that’s more positively charged. Water tends to arrange itself so that the negative end of one molecule is pointing toward the positive end of another.
Water is very good at dissolving and washing away other things that are polar. They interact well with water and water is able to carry them away. Non-polar things, like most oils and fats, don’t interact well with water. Soaps contain surfactants, these are molecules that have both a polar and non-polar part of them. They interact well with both water and oils and therefore can help water dissolve and carry away non-polar molecules.
One of the things that I remember from chemistry class…
**Like dissolves like**
Water can’t dissolve oil, but other oils can.
The fats and oils in soap have been changed in the process of making them into the soap. This change allows them to cling to both water and oils; since you rinse with water, that carries the soap-oil mix away with it, leaving your skin oil-free.
Fats already have a fat-friendly part. The soap-making adds a water-friendly part. Now you have soap, that can enclose fat in a layer of (outward) water friendly soap.
There’s a rule of thumb in chemistry that similar substances dissolve each other well (“like dissolves like”). So fats and oils can dissolve other fats and oils, but don’t dissolve well in water. But soap dissolves in water -what’s going on?
Normal fats and oils are triglycerides- three fatty acid chains (think long chains of carbons and hydrogens) attached to a glycerin backbone. When making soap, triglycerides are reacted with a strong base (eg potassium hydroxide) in a reaction called saponification, which causes the glycerin backbone to break off and the free fatty acids to form a salt with the potassium (or sodium if using NaOH) ions. Now the ionic end (the “head”) of the fatty acid salts dissolve well with water, and the tail of the fatty acid dissolves well with oils. And now we have something that can mix with both water and oils!
When you wash with soap, the tail ends of the soap molecules attract oils on your skin, and the “head” of the soap molecules attract water. Because each end wants to be with its “own kind”, a bunch of soap molecules end up arranging themselves in a “bubble” where all the tails point inward, trapping a little ball of oil, and all the heads point outward, forming the water-soluble outside surface of this little bubble, called a micelle, and then all the micelles rinse away with the water.
the fats are boiled in either a strong acid (liquid soap) or lye (solid soap)
the electo molecular polarity means it attaches to the more neutral fats
Water is polar, so a part of its molecule is charged positive, and other part is charged negative. Oils and fats are non-polar, there is no charge difference across the molecule. Polar solvents dissolve polar molecules, and nonpolar solvents dissolve nonpolar molecules. Soap is made from fats, but during the saponification reaction fat molecules are modified: before the reaction they look like a pitchfork, with three long molecules joined at one base. Adding a base like NaOH breaks teeth off that pitchfork, with Hydrogen attaching to the pitchfork base making it into glycerin, and Na and O attach to cut off ends of pitchfork teeth, turning them into and interesting molecule: molecule body itself still has no charge, but the end with oxygen and sodium attached has charge. So now we have an “adapter” molecule: neutral part interacts well with nonpolar substances, and charged end interacts well with water or other polar solvents. Now water can interact with grease through this molecule and dissolve things that were not soluble before
Because the fats and oils are changed being made into soap… they all put on little leather jackets and get switchblades. Start talking about “their turf” and stuff. It’s basically gang warfare in a bottle.
Actually, it’s expressly because it’s made of oil!
Water and oil don’t tend to mix well; they got different chemistry ;). But this means it can be really hard to wash food grime with just water; fat sticks to the plate, and tells the water to beat it.
But, soap is a cool compound. One half of it is fine touching water, and the other end is good with oils like fat! So soap is essentially the best cleaning middleman you could ask for!
You can cover the fats in soap, then dissolve the soap in water, and because the fat and water aren’t touching eachother, everything’s cool!
Consider soap molecules to be a magnet which attracts both oil and water. Whereas water and oil don’t. So you need something which attracts both or just oil to clean something.
Dry cleaning works by washing clothes in an organic compound like petrol or acetone. Which dissolves oil.
Try this at home : Put some oil and water in a glass and try to mix them. Now add just a pinch of detergent and mix them. You’ll understand what i mean.
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