In osmosis, there is a net flow of solvent molecules from the solvent to the solution or from a less concentrated solution to a more concentrated solution across a semipermeable membrane (membranes of animal origin, membranes made from
Cu2 [Fe (CN) 6], Ca3 (PO4)2 etc.)
Osmosis was first observed by Abbe Nollet in 1748.
Osmotic pressure is the equilibrium hydrostatic pressure of the column set up as a result of osmosis. It is the minimum pressure that must be applied on the solution to prevent the entry of the solvent into the solution through the semipermeable membrane. It is the minimum pressure needed to apply on a solution to make its vapour pressure equal to vapour pressure of the solvent.
- It is denoted by P or π.
- It is measured by Pfeiffer’s method, BerkelyHartley’s method, Townsend’s method.
Van’t Hoff equation of osmotic pressure
π = CST
Here, π = Osmotic pressure
C = Concentration of solution in mol/L
S or R = Solution constant
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