Question

The density of a solution prepared by dissolving $120g$ of urea (mol.mass$=60u$) in $1000g$ of water is $1.15g/mL$. The molarity of this solution is:

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

Answer 1

The correct option is C $2.05M$

Mass of solute = $120g$

Mass of solvent = $1000g$

Mass of solution = $1120g$

Density of solution = $1.15g/mL$

No of moles of solute = $\frac{120}{60}=2mol$

Volume of solution =$\frac{mass}{density}=\frac{1120}{1.15}$

Molarity = $\frac{n\times 1000}{V}=\frac{2\times 1.15\times 1000}{1120}=2.05M$