Calculate the mass of urea (NH2CONH2) required in making 2.5 kg of 0.25 molal aqueous solution.
Molality = (w x 1000) / (mm x W)
Mass of solution = 2.5 kg = 2500 gms
0.25 mole of urea = 0.25 × 60 = 15g
Therefore mass of solvent = 2500 - 15
0.25 = (w x 1000) / (60 x 2485)
w = 37.25 gms