Cleaning with Soap

When soap comes in contact with water, the water is strongly attracted to the polar or ionic end of the soap. So, if there is soap on your hands and you run them under water, the water will grab on to the soap molecules and pull them down the drain.

If all you've done is squirt some liquid soap on the surface of your greasy hands then the soap and water will go down the drain and leave the grease on your hands.

However, you won't do that. Anyone washing their greasy hands knows that they need to scrub their hands well with the soap before rinsing them. This process helps the long non-polar chains of the soap molecules to wrap around the long, non-polar chains of the grease molecules.

These chains will mix easily because they are both non-polar, and although the attractions between non-polar molecules is fairly weak (London Dispersion Forces) the chains are so long that the large amount of surface area makes the attraction fairly substantial.

Then, when you rinse your hands with water, the water molecules will be attracted to the polar or ionic end of the soap molecules and pull them down the drain. However, since you have made the effort to mix the non-polar chains of the soap and grease, as the soap goes down the drain, it will pull the grease along with it.