Question

A solution containing \(10 \mathrm{~g}\) per \(\mathrm{dm}^{3}\) of urea (molecular mass \(=60 \mathrm{~g} \mathrm{~mol}^{-1}\) ) is isotonic with a \(5 \%\) solution of a nonvolatile solute is
(a) \(200 \mathrm{~g} \mathrm{~mol}^{-1}\)
(b) \(250 \mathrm{~g} \mathrm{~mol}^{-1}\)
(c) \(300 \mathrm{~g} \mathrm{~mol}^{-1}\)
(d) \(350 \mathrm{gmol}^{-1}\)

Answer 1

Correct option (c) \(300 \mathrm{~g} \mathrm{~mol}-1^{1}\)
Explanation :
For isotonic solution,
osmotic pressure of urea = osmotic pressure of nonvolatile solute
$$
\begin{aligned}
&\frac{10}{60 \times 1000}=\frac{5}{m \times 100} \\
&\Rightarrow m=300 \mathrm{~g} \mathrm{~mol}^{-1}
\end{aligned}
$$