Question

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

Answer 1

Density of the solution:

1.15 g mL= Mass/Volume

=(1000+120)/V

>V=

$\frac{1120}{1.15} = 973.91$

no.of moles of solute=

$\frac{120}{60} = 2$

molarity=(no.of moles of solute /volume of solution)×1000

=

$\frac{2}{973.91} \times 1000 = 2.05$

ans: 2.05M

Answer 2

2.05 M

To calculate the molarity of the solution we must know the:

(i) Number of Moles of Urea

(ii) Total Volume Of Solution

(i) Calculating Number Of Moles Of Urea which is dissolved in the solution:

= Total Mass / Molar Mass

= 120 g / 60 g

= 2

(ii) Calculating Total Volume Of the Solution:

= Mass Of Urea + Mass of Water

= 120 g + 1000 g

= 1120 g

Volume of the total solution:

= Total Volume / Density

= 1120 g / 1.15g/mL

= 974 mL

Converting this to Liters we get:

= mL / 1000

= 974 / 1000

= 0.974 liters

Molarity of solution:

= No of moles / Volume of Solution

= 2 / 0.974

= 2.05 M

Therefore, the molarity of the solution is 2.05 M.