Question

18 g glucose and 6 g urea are dissolved in 1 litre aqueous solution at ${27}^{\circ }C$. The osmotic pressure of the solution will be:

• A. 4.3
• B. 5.69
• C. 3.45
• D. 3.65

Answer 1

The correct option is A 4.3

We know that colligative properties depend only on the number of particles of solute and not on the type or nature of the solute present. Therefore, the amount of solute present is our only concern, whether it is glucose or urea.

So, we know
$\pi \ast V=n\ast R\ast T$

Let's use $n_1$ and $n_2$ here, to denote moles of glucose and moles of urea.
$n=n_1+n_2$

$\pi \ast V=(n_1+n_2)\ast R\ast T$

$n_1=\frac{18}{180}=0.1mol$

$n_2=\frac{6}{60}=0.1mol$

$Therefore,\pi \ast \left(1\right)=(0.1+0.1)\ast 0.082\ast (273+27)$

$\Rightarrow \pi =4.296atm$

Rounding off gives 4.3