Mass of water = 71.6 g = 0.0716 kg Molality = moles of urea/mass of water in kg = 2.4 m = 2.4 mol/kg moles of urea required = 2.4 x 0.0716 = 0.172 mol Solution Mass of water = 71.6 g = 0.0716 kg Molality = moles of urea/mass of water in kg = 2.4 m = 2.4 mol/kg moles of urea required = 2.4 x 0.0716 = 0.172 mol.