Question

A decimolar solution of potassium ferrocyanide is 50% dissociated at 300 K. Calculate the osmotic pressure of the solution.

Answer 1

$K_4\left[Fe{\left(CN\right)}_6\right]\to 4K^{\oplus }+{\left[Fe{(CN}_6\right]}^{4-}$
Initial 1 0 0
At eq. $1-\alpha$ $4\alpha$ $\alpha$

Total moles at equilibrium $=1-\alpha +4\alpha +\alpha =1+4\alpha$

$\alpha =50\%=0.5$ (given)

$\therefore i=\frac{1+4\alpha }{1}=1+4\times 0.5=3$

Using the formula, $\pi =iMRT$

$=3\times 0.1\times 0.082\times 300=7.38$ atm.