What’s the process that makes it good at something so far off from its composition?
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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.
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