What is osmotic pressure? Explain and derive its equation.

(N/A) The flow of the solvent from its side to the solution side across a semipermeable membrane can be stopped if some extra pressure is applied on the solution. This pressure that just stops the flow of solvent is called osmotic pressure $(\Pi)$ of the solution.
The flow of solvent from a dilute solution to a concentrated solution across a semipermeable membrane is due to osmosis. Solvent molecules always flow from a region of lower solute concentration to a region of higher solute concentration. Osmotic pressure is a colligative property as it depends on the number of solute particles.
For dilute solutions,osmotic pressure $(\Pi)$ is proportional to the molarity $(C)$ of the solution at a given temperature $(T)$.
$\Pi \propto C$
$\Pi = C R T$
Since molarity $C = \frac{n_{2}}{V}$,where $n_{2}$ is the number of moles of solute and $V$ is the volume of the solution in litres,we have:
$\Pi = \frac{n_{2}}{V} R T$
If $w_{2}$ is the mass of the solute and $M_{2}$ is its molar mass,then $n_{2} = \frac{w_{2}}{M_{2}}$. Substituting this into the equation:
$\Pi = \frac{w_{2} R T}{M_{2} V}$
Thus,knowing the values of $w_{2}, T, \Pi$ and $V$,we can calculate the molar mass $(M_{2})$ of the solute.