Colligative Properties

Step 1: Define Osmosis.
Osmosis is the movement of solvent molecules from a region of lower solute concentration to a region of higher solute concentration, through a semi-permeable membrane. This continues until equilibrium is reached.
Step 2: Molar Mass Determination by Boiling Point Elevation.
The relationship between the boiling point elevation ( ) and molality ( ) of a solution is given by: Where: - is the boiling point elevation, - is the ebullioscopic constant of the solvent, - is the molality of the solution. To calculate the molar mass, rearrange the formula to find:

The cryoscopic constant, also known as the freezing point depression constant, is used to calculate the depression in freezing point when a solute is added to a solvent. The SI unit of the cryoscopic constant is: This unit corresponds to the change in freezing point per unit molality (moles of solute per kilogram of solvent).

Concept:
When a non-volatile solute is added to a solvent, the vapour pressure of the solution decreases. This lowering of vapour pressure leads to several related properties known as colligative properties.
Colligative Properties:
Colligative properties are those properties of solutions that depend only on the number of solute particles present, not on their nature.
Examples of Colligative Properties:

Lowering of vapour pressure
Elevation of boiling point
Depression of freezing point
Osmotic pressure All these properties arise due to the decrease in vapour pressure when solute is added.