What is the molality of 40% (by mass) urea solution?
Answer & explanation
Correct answer: option 3
40% (by mass) urea solution means 40 g urea is present in 100 g solution.
Mass of solvent = 100 - 40 = 60g
Molecular mass of urea (NH2CONH2) = 60 g/mol
No of moles of urea = \(\frac{40}{60}\) = \(\frac{2}{3}\)
Molality = \(\frac{\text{no of moles of solute}}{\text{Mass of solvent(in g)}}\) x 1000 = \(\frac{2}{3 × 60}\) x 1000
m = \(\frac{100}{9}\) = 11.11