Answer:
136.5°C
Explanation:
Given data
- Boiling point of X: 134.5°C
- Molal boiling point elevation constant (Kb): 1.36·°C·kg.mol⁻¹
We can calculate the elevation in the boiling point (ΔT) using the following expression.
ΔT = Kb × m
where,
m is the molality
The molar mass of urea is 60.06 g/mol. The moles of urea corresponding to 76 g is:
76 g × (1 mol/60.06g) = 1.3 mol
The mass of the solvent (X) is 850 g = 0.850 kg.
The molality is:
m = 1.3 mol / 0.850 kg = 1.5 mol/kg
Then,
ΔT = Kb × m
ΔT = 1.36·°C·kg.mol⁻¹ × 1.5 mol/kg
ΔT = 2.0 °C
The boiling point of the solution is
134.5°C + 2.0°C = 136.5°C
