##### Exercise | Q 3.6 | Page 46

# Answer the following.

## How molar mass of a solute is determined by osmotic pressure measurement?

### Solution

1. For very dilute solutions, the osmotic pressure follows the equation,

$\pi =\frac{{\text{n}}_{2}\text{RT}}{\text{V}}$ ....(1)

2. If the mass of solute in V litres of a solution is W2 and its molar mass is

$\text{M}}_{2$ , then $\text{n}}_{2}=\frac{{\text{W}}_{2}}{{\text{M}}_{2}$

Substituting the value of n_{2} in equation (1), we get

$\pi =\frac{{\text{W}}_{2}\text{RT}}{{\text{M}}_{2}\text{V}}$

∴ $\text{M}}_{2}=\frac{{\text{W}}_{2}\text{RT}}{\pi \text{V}$

This formula can be used for the calculation of molar mass of a nonionic solute (i.e., nonelectrolyte), by osmotic pressure measurement.

1. For very dilute solutions, the osmotic pressure follows the equation,

2. If the mass of solute in V litres of a solution is W2 and its molar mass is

Substituting the value of n_{2} in equation (1), we get

∴

This formula can be used for the calculation of molar mass of a nonionic solute (i.e., nonelectrolyte), by osmotic pressure measurement.