Question

Calculate the boiling point of urea solution when 6 g of urea is dissolved in 200 g of water.
(K_b for water = 0.52 K kg mol^–1, boiling point of pure water = 373 K, mol. wt. of urea = 60)

Answer 1

Given: Mass of urea = 6 g

Molar mass of urea = 60 g/mol

Mass of water = 200 g = 0.2 kg

K_b = 0.52 K kg mol⁻¹

Boiling point of pure water = 373 K

Moles of urea = `6/60`

= 0.1 mol

Molality = `(0.1 mol)/(0.2 kg)`

= 0.5 mol/kg

ΔT_b = K_b m

= 0.52 × 0.5

= 0.26 K

T_b = 373 + 0.26

= 373.26 K

∴ The boiling point of the urea solution is 373.26 K.