Question

The osmotic pressure of two aqueous urea solutions-I and II are $2.1atm\text{and}1.8atm$ respectively at ${25}^{\circ }C$. The osmotic pressure (in atm) of a solution at ${25}^{\circ }C$ prepared by mixing solution I and II in the volume ratio of $2:1$ is

Answer 1

Osmotic pressure $\left(\pi \right)=iCRT$
$i=1$
${\pi }_1=C_{1}RT⟹C_1=\frac{2.1}{RT}$
$C_2=\frac{1.8}{RT}$
$C\text{(no mixing)}=(\frac{2.1\times 2}{RT}+\frac{1.8}{RT})\times \frac{1}{3}=\frac{2}{RT}$
$\therefore \pi =CRT=\frac{2}{RT}\times RT=2atm$.