Question

Dissolving $120$ g of urea (mol. wt. is 60) in $1000$ g of water gave a solution of density $1.15$ g/ml. The molarity of the solution is :

• A. 1.78 M
• B. 2.00 M
• C. 2.05 M
• D. 2.22 M

Answer 1

The correct option is C 2.05 M

$Molarity=\frac{\text{Moles of solute}}{\text{Volume of solution (L)}}$.

$\text{moles of urea}=\frac{120}{60}=2$.

$Weightofsolution=weightofsolvent+weightofsolute=100+120=1120g$.

$Volume=\frac{Massofsolution}{Density}=\frac{1120g}{1.15g/mL}\times \frac{1}{1000ml/L}=0.974L$.

Substitute the values in the expression for the molarity of solution.

$Molarity=\frac{2.000}{0.974}=2.05M$.

So, the correct option is $C$