Soap plays a large role in most of our lives. It keeps us clean, makes us smell good, and is lots of bubbly fun. There are tons of different types for washing all different kinds of things. From hair to cars, there is soap for almost everything. It's strongly integrated into our lives, yet for many, if they were asked how it works, they couldn't tell you.
Why is soap so much more effective than plain water?
The answer lies in chemistry.
Above is our friend Bob The Dirt. Bob and most of his oily and greasy friends are non-polar compounds. What does this mean? Well, in order for a molecule to dissolve in another molecule, they must have the same polarity. So, since water is a polar molecule, Bob and his non-polar friends will not dissolve in it. This is why trying to wash your hands without soap after eating a greasy burger isn't very effective.
How do we solve this problem and avoid dirty hands? Soap!
The structure of soap is what makes it work. Soap molecules have two different ends on them. One end is a hydrocarbon chain which is non-polar and binds with the Bob and his friends. This end of the soap molecule is hydrophobic, meaning it is repelled by water. The other end of the soap molecule is a polar ionic end which will bind with water and polar food particles. This end is hydrophilic, meaning it's attracted to water.
The magic starts to happend when you mix soapy water with grease and dirt as you begin to wash your hands. During this, the soap molecules arrange themselves into clusters around Bob and his friends. These clusters are called micelles. The hydrophilic heads of the soap molecules form the outside of the micelle and allow it to suspend in water. The hydrophobic ends of the soap molecules trap Bob's gang in the middle of the micelle where they can't come in contact with water. With the oils trapped in the center, the micelle is soluble in water. So, as the soapy water gets washed down the drain, Bob and every other greasy bit of dirt on your hands gets washed away with it.
So now you know, if you didn't already. Next time you're washing your hands in a public restroom, you can lean over to the stranger at the sink next to you and give them a mini chemistry lesson on the miracle that's happening in front of them. Who knows? Maybe you'll make a new friend.