Question

The measured osmotic pressure of a solution prepared by dissolving $17.4\, mg$ of $K_2SO_4$ in $2L$ of water at $27 {^{\circ}C}$ is $3.735 \times 10^{-3}$ bar. The Van' t Hoff factor is
($R = 0.083 \, L$ bar $K^{-1}\, mol^{-1}$ : atomic weights $K = 39 : S = 32 : O = 16$)

• A. 2.84
• B. 3.0
• C. 2.0
• D. 2.32

Answer 1

Answer: (B)

Given, $\pi=3.735 \times 10^{-3}$ bar

Mass of $K _{2} SO _{4}(\omega)=17.4\, mg$

Volume $=2\, L$

Temperature $(T)=27^{\circ} C =27+273=300\, K$

From osmotic pressure of solution.

$\pi =i C R T$

$i =$ van't-Hoff factor

$i =\pi / C R T$

$=\frac{\pi \times M \times V}{\omega \times R \times T}=\frac{3.735 \times 174 \times 2}{17.4 \times 0.083 \times 300}$

Molar mass $(M) H _{2} SO _{4}=174,\, i=3.0$