Question

A $5.25\%$ solution of a substance is isotonic with $1.5\%$ solution of urea (molar mass $=60gmol^{- 1}$ ) in the same solvent. If the densities of both the solutions are assumed to be equal to $1.0gcm^{- 3}$ , molar mass of the substance will be :

• A. $90.0gmol^{- 1}$
• B. $11.50gmol^{- 1}$
• C. $105.0gmol^{- 1}$
• D. $210.0gmol^{- 1}$

Answer 1

Answer: (D)

$\pi _{1}=\pi _{2}$
$\left[\right.C\left]\right._{sol}=\left[\right.C\left]\right._{\text{urea }}$
$\frac{5 . 25}{M}=\frac{1 . 5}{60}$
$\Rightarrow M=\frac{5 . 25 \times 60}{1 . 5}$
$=210$