Question

The density of a solution prepared by dissolving $120g$ of urea (Mol. Mass $=60u$) in $1000g$ of water is $1.15g/mol$. The molarity of this solution is
(AIEEE 2012)

• A. $1.02M$
• B. $0.50M$
• C. $1.78M$
• D. $2.05M$

Answer 1

The correct option is D $2.05M$

We know that
$textMolarity\left(M\right)=\frac{\text{No. of moles of solute}}{\text{Volume of solution in litre}}$

$\text{Moles of solute}=\frac{120}{60}=2$

$\text{Mass of the solution}=1000+120=1120gm$

$\text{Density of solution}=1.15g/ml$

$\therefore \text{Volume of the solution}=\frac{1120}{1.15}$

$=973.9ml=\frac{973.9}{1000}litre=0.9739litre$

$\therefore M=\frac{2}{0.9739}=2.05$