Question

The density of a solution prepared by dissolving 120 g of urea (mol. Mass = 60 u) in 1000 g of water iws $1.15 \mathrm {~g} / \mathrm { mL }$ the molarity of this solution is

• A.
• B.
• C. $2.05 M$
• D.

Answer 1

Answer: (C)

$2.05 M$

Answer 2

Mass of solute taken = 120 g

Molecular mass of solute = 60 u

Mass of solvent = 1000 g

Density of solution = $1.15 \mathrm {~g} / \mathrm { mL }$

Total mass of solution

Volume of solution $= \frac { \text { Mass } } { \text { Density } } = \frac { 1120 } { 1.15 } \mathrm {~mL}$

Molartiy $= \frac { \frac { \text { Mass of solute } } { \text { Molecular mass of solute } } } { \text { Volume of solution } } \times 1000$

$= \frac { 120 / 60 } { 1120 / 1.15 } \times 1000 = \frac { 2 \times 1000 \times 1.15 } { 1120 } = 2.05 \mathrm { M }$