Question

A decimolar solution of potassium ferrocyanide is $50\%$ dissociated at 300K. The osmotic pressure of the solution is:

• A. 2.4101 atm
• B. 1.5420 atm
• C. 7.389 atm
• D. 10.1281 atm

Answer 1

The correct option is C 7.389 atm

We are given a decimolar solution of $K_4\left[Fe\right(CN{)}_6]$, molarity = 0.1 M
Degree of dissociation $\left(\alpha \right)=\frac{50}{100}=0.5$
Potassium ferrocyanide dissociates to give,
$K_4\left[Fe\right(CN{)}_6]\to 4K^{+}+[Fe(CN{)}_6{]}^{4-}$
Hence n = 5
$\alpha =\frac{i-1}{n-1}$
$0.5=\frac{i-1}{5-1}$
$i-1=2$
$\therefore i=3$
$\therefore$ van't Hoff factor is 3
$\pi =i\times c\times R\times T$

$\pi =3\times 0.1\times 0.0821\times 300$
$=7.389\text{atm}$