Answer the following. How molar mass of a solute is determined by osmotic pressure measurement? - Chemistry

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,

${\displaystyle \pi =\frac{{\text{n}}_2\text{RT}}{\text{V}}}$        ....(1)

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

${\displaystyle {\text{M}}_2}$, then ${\displaystyle {\text{n}}_2=\frac{{\text{W}}_2}{{\text{M}}_2}}$

Substituting the value of n₂ in equation (1), we get

${\displaystyle \pi =\frac{{\text{W}}_2\text{RT}}{{\text{M}}_2\text{V}}}$

∴ ${\displaystyle {\text{M}}_2=\frac{{\text{W}}_2\text{RT}}{\pi \text{V}}}$

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