Answer:
42.8 g was the mass of dissolved urea.
Explanation:
Boiling point elevation to solve this:
ΔT = Kb . m
where ΔT → Boiling T° of solution - Boiling T° of pure solvent
Let's replace the data given:
118.3°C - 117.8°C = 0.63°C/m . m
0.5°C / 0.63 m/°C = m → 0.793 mol/kg
Mass of solvent → 900 g → g to kg → 900 g . 1kg/1000 = 0.9 kg
Molality . kg = moles → 0.793 mol/kg . 0.9 kg = 0.714 mol
These are the moles of urea we used. Let's determine the mass dissolved.
0.714 mol . 60 g /1mol = 42.8 g
