Question

PROBLEM 2.5
11.11 g of urea was dissolved in 100 g of water. Calculate the molality of solution. (N=14, H=1. C=12, O=16]​

Answer 1

1.852 mol kg^-1

Given:

Mass of solvent = 11.11 grams

Mass of solution = 100 grams = 0.1 kg

To Find:

Molality of the solution

Solving:

Calculating Molecular mass of Urea = (NH2CONH2)

= 2 x 14 g + 4 x 1 g + 12 g x 1 + 16 g x 1

= 28g + 4g + 12g + 16g

= 60 g mol^-1

No of moles in urea = Given Mass / Molecular Mass

= 11.11 g / 60 g mol^-1

= 0.1852 mol

Calculating the volume of water:

= Mass of water / Density

= 100 g / 1 g mL^-1

= 100 mL

Converting into liters:

= 100 / 1000

= 0.1 Liters

Calculating Molality of the solution:

= Number of moles of solute / Mass of solvent in kg

= 0.1852 kg mol / 0.1 kg

= 1.852 mol kg^-1

Therefore, the Molality of the solution is 1.852 mol kg^-1.