Question

1.) A 238 mL solution has an osmotic pressure of 0.398 atm at a temperature of 32°C. If 0.312 g of solute was added to the solution, what is the molar mass of the solute?

Answer 1

The osmotic pressure of the solution can be expressed as

$$\pi=i\frac{nRT}{V},\\ n=\frac{\pi V}{RT}.$$

if the van't Hoff coefficient is $i=1$.

The molar mass is

$$\Mu=\frac{m}{n}=\frac{mRT}{\pi V}=\frac{0.312\cdot8.314(32+273)}{0.398\cdot10^5\cdot238\cdot10^{-6}}=83.5\text{ g/mol}.$$