- Osmotic pressure arises when two solutions of different concentrations, or a pure solvent and a solution, are separated by a semipermeable membrane.
Molecules such as solvent molecules that can pass through the membrane will migrate from the side of lower solute concentration to the side of higher solute concentration in a process known as osmosis.
So the dilute solution becomes more concentrated over time, and at the same time, the concentrated solution becomes more dilute.
- The pressure required to stop osmosis is called the osmotic pressure.
- In dilute solutions, osmotic pressure (Π) is directly proportional to the molarity of the solution (c) and its temperature in Kelvin (T).
Π ∝ cT
- van't Hoff Equation: Π = cRT
Π = osmotic pressure
c = molarity = moles ÷ volume (L)
R = ideal gas constant
T = temperature (K)
- Solvent can be removed from a solution using a pressure greater than the osmotic pressure.
This is known as reverse osmosis.