Osmotic Pressure
The external pressure that must be applied to a solution to prevent the inward flow of solvent through a semipermeable membrane.
Formula / equation
π = i M R T
Unit
atm
In depth
Osmotic pressure is the largest of the colligative effects and can be measured with high precision even in very dilute solutions, which makes it the preferred method for determining the molar masses of polymers and proteins. It rises directly with the total particle concentration.
Examples in the real world
A 0.1 M glucose solution exerts about 2.4 atm at 25 °C; blood plasma is close to 7.6 atm.