Question

Calculate the osmotic pressure at ${25}^{o}C$ of a solution containing 1 g of glucose and 1 g of sucrose in 1 litre of solution.
If it were not known that the solute was a mixture of glucose and sucrose, what would be the molecular weight of solute corresponding to the calculated osmotic pressure?

Answer 1

Ans. 0.207 atm, 236.384
Use; $\pi V=(n_1+n_2)RT$ to calculate osmotic pressure
$\pi \times 1=\left(\begin{array}{c}\frac{1}{180}+\frac{1}{342}\end{array}\right)\times 0.0821\times 298$
$=0.207atm$
Use; $\pi V=\frac{w}{m}RT$ to calculate molar mass of solute.
$0.207\times 1=\frac{2}{m}\times 0.0821\times 298$
$m=236.384$