Question

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

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

Answer 1

Answer: (C)

Molarity $=\frac{\text{ Moles of solute }}{\text{ Volume of solution (L) }}$
Moles of urea $=\frac{120}{60}=2$
Weight of solution $=$ Weight of solvent $+$ Weight of solute
$=1000+120=1120g$
$\Rightarrow$ Volume $=\frac{1120g}{1.15g/mL}\times \frac{1}{1000mL/L}=0.973L$
$\Rightarrow$ Molarity $=\frac{2.000}{0.973}=2.05M$