Molality is defined as the number of moles of solute in 1 kg of solvent . the mass of water - 512.85 ml x 0.975 g/ml = 500 g number of moles of solute in 500 g of water - 171 g / 342.30 g/mol = 0.500 mol the number of sucrose moles in 500 g of water - 0.500 mol therefore number of sucrose moles in 1 kg water - 0.500 mol / 0.500 kg = 1.00 molality of solution - 1.00 M