Question

A decimolar solution of potassium ferrocyanide at $300K$ is $50\%$ dissociated. Calculate the osmotic pressure of the solution.
$R=0.082Latmmo{l}^{-1}{K}^{-1}$.

• A. $\pi =14.18atm$
• B. $\pi =7.38atm$
• C. $\pi =1.45atm$
• D. $\pi =21.91atm$

Answer 1

The correct option is B $\pi =7.38atm$

$K_{4}Fe{\left(CN\right)}_6\rightleftharpoons 4K^{+}+{\left[Fe{\left(CN\right)}_6\right]}^{4-}$

As one molecule of potassium ferrocyanide dissociates into five particles.
So, $n=5$
$\text{Degree of dissociation,}\alpha =50\%=0.5$
For dissociation,
$\alpha =\frac{i-1}{n-1}$

$0.5=\frac{i-1}{5-1}$

$i=3$

$\text{Osmotic pressure,}\left(\pi \right)=iCRT$

Given:

$\text{Concentration,}C=\frac{1}{10}mol{L}^{-1}$

$R=0.082Latmmo{l}^{-1}{K}^{-1}$

$T=300K$

$\pi =\frac{3\times 1\times 0.082\times 300}{10}\pi =7.38atm$