If I add 45 grams of sodium chloride (NaCl) to 450 mL of water.
What is the molality of this solution?
Solution: Molality = moles of solute/kg of solvent
45g of NaCl ( 1mol/ 58.44 g) = 0.77mol of NaCl
Density of water is 1g/ml. 450ml = 450 g of water/1000 = 0.45kg
molality = 0.77mol of NaCl/.45kg = 1.7 mol/kg