Chemistry class 12th Osmosis and osmotic pressure

Osmosis and Osmotic Pressure


1. Introduction

Osmosis is the process of movement of solvent molecules from a region of lower solute
concentration to a region of higher solute concentration through a semipermeable membrane. This
process continues until equilibrium is reached.


Osmotic pressure is the pressure required to stop the osmosis process. It is a colligative property
that depends on the concentration of solute particles, not their identity.


2. Definition and Explanation


**Osmosis:** The spontaneous movement of solvent molecules across a semipermeable membrane
toward a higher solute concentration.


**Osmotic Pressure:** The minimum pressure needed to prevent the net movement of solvent
molecules through a semipermeable membrane.


3. Formula and Derivation


Osmotic pressure (Pi) is given by Van't Hoff's equation:


Pi = nRT / V


or in terms of molarity (C):
Pi = CRT


where:
- Pi = Osmotic pressure
- C = Molar concentration of the solution (mol/L)
- R = Universal gas constant (0.0821 L atm mol-¹ K-¹)
- T = Temperature in Kelvin