Question

Determine the osmotic pressure of a solution prepared by dissolving $25mg$ of $K_{2}S{O}_4$ in $2$ litre of water at ${25}^{\circ }C$, assuming that it is completely dissociated.

Answer 1

For complete dissociation of potassium sulphate, $K_{2}S{O}_4\rightleftharpoons 2K^{+}+S{O}_4^{2-}$, the Van't Hoff's factor (i) is 3.

The molar mass of potassium sulphate is $174$ g/mol.

According to Van't Hoff's equation,

$\Pi =iCRT$

Where $\Pi =$ osmotic pressure

$C=$ molar concentration of potassium sulphate

$W_B=$ Mass of potassium sulphate

$M_B=$ Molar mass of potassium sulphate

$\Pi =\frac{W_{B}RT}{M_{B}V}$

$\Pi =\frac{3\times 25\times {10}^{-3}\times 0.082\times 298}{174\times 2.0}=5.27\times {10}^{-3}$ atm