Transcript
Why does a potato shrink in salty water?
Osmosis is the diffusion of water from a dilute solution to a more concentrated solution through a partially permeable membrane. Learn that definition word for word: most students forget the part about the partially permeable membrane.
Zoom in on the membrane. Water molecules are small enough to pass through. Solute particles are too big. So there is a net movement of water to the concentrated side.
In the required practical, potato cylinders go into different salt solutions. Plot the percentage change in mass. Where the line crosses zero, there's no net movement of water: that's the same concentration as inside the potato cells.
Exam question: why do students calculate the percentage change in mass? Not "to make it fair": the potato pieces had different starting masses, so percentage change lets you compare them.
