How to calculate molality with density and molarity?

Chemistry - How do I calculate molality from molarity and density?

• Calculate the molality of HCl from the following data: Formula weight(amu) = 36.465 Density of solution (g/mL) = 1.19 Weight % = 37.2 Molarity = 12.1 moles solute/L solution I think the molality should end up being 6.02 moles solute/kg solvent but i don't know how to calculate this because I got the answer from someone else who didn't show their work. Help?

• Answer:

  The weight percent will help you more here, though you can get it from density and molarity. From weight percent: 37.2% would mean 37.2 g HCl out of 100 g of solution, leaving you 62.8 g of solvent. 37.2 g is 1.02 moles while 62.8 g of solvent is 0.0628 kg. Molality is 1.02/0.0628 or 16.2 m. From density and molarity: If the density is 1.19 g/ml, a liter of solution will weigh 1190 g. There are 12.1 moles solute in that 1190 g, which will weigh 441.7 g. The amount of solute is then 1190 - 441.7 or 748.3 g or 0.7483 kg. Molality is then 12.1 moles/0.7483 kg or 16.2 m (with rounding). Whoever that someone else is, tell them they're wrong.