molality is the number of moles of solutes in 1 kg of solvent. the molality of solution to be prepared is 2.0 molal. therefore 2 moles in 1 kg water. the mass of Li₂S required is - 46 g/mol x 2.0 mol = 92 g the mass in 1 kg of solvent is - 92 g Therefore mass of Li₂S required in 1600.0 g is - 92 g/kg x 1.6 kg = 147.2 g
