Q. Dissolving 120 g of urea (mol. Wt. 60) in1000 g of water gave a solution of density 1.15 g/mL. The molarity of the solution is
A) 1.78M
B) 2.00M
C) 2.05M
D) 2.22M
Explanation
(c)
Molarity =$\frac{Moles\ of\ solute}{Volume\ of\ solution(L)}$
moles of urea =$\frac{120}{60} = 2$
weight of solution =weight of solution + weight of solute
=1000 + 120 =1120 g
$\Rightarrow \ Volume\ = \frac{1120g}{\frac{1.15g}{mL}} \times \frac{1}{1000mL/L}$
=0.974 K
$\Rightarrow$Molarity = $\frac{2.000}{0.974}$= 2.05 M
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.