Van t Hoffs law for osmotic pressure

When two compartments containing a pure solvent and a solution (i.e., solute + solvent) are separated by a semipermeable membrane, that is a membrane that allows the transport of the molecules of the solvent while it retains the molecules of the solute, the solvent flows across the membrane to the compartment containing the solution until equilibrium is reached. This process is called osmosis and the differential pressure created between the two compartments is called the osmotic pressure denoted ta Osmosis was first studied quantitatively by the botanist W.P.F Pfeffer in 1877 and later Jacobus Henricus Van t Hoff found that the osmotic pressure of dilute solutions obeys a relationship of the same form as the ideal gas law and is now called the Van t Hoff law for osmotic pressure. If the osmotic pressure was exerted by the solute alone, it was acting as an ideal gas and its molecules occupied a volume equal to that of the volume of the solution, then... 

The van t Hoff Law for osmotic pressure (Equation 5.19) depends explicitly on the molecular weight of the solute. One of the most remarkable properties of semidilute solutions is that the osmotic pressure is observed to be independent of the molecular weight of the macromolecules. Another property fliat is observed to be independent of molecular weight in semidilute solution is the mutual-diffusion coefficient, DJ c). These phenomena are discussed in Section 6.2 and explained in more detail in Section 6.3. 

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