Oil doesn't push water away
- The idea
- Predict
- See it
- Why
- Check
The idea
“Hydrophobic molecules repel water. Oil actively pushes water away.”
"Water fearing" makes it sound like oil does something to water. Water is the one doing the work.
The short version
The mistake: Hydrophobic molecules repel water. Oil actively pushes water away.
What's actually true: Nothing pushes. Water molecules hydrogen bond with each other and leave nonpolar molecules out, so those end up together.
- Water is polar. Each molecule hydrogen bonds with its neighbors, the slightly negative oxygen of one to a slightly positive hydrogen of another.
- Oils and other nonpolar molecules have no partial charges for water to hydrogen bond with. That's what hydrophobic means.
- The same thing happens in cells. It keeps the fatty acid tails of phospholipids tucked inside the membrane, away from water.
On the exam: Hydrophobic doesn't mean pushed away. Water bonds with itself and leaves nonpolar molecules out.