Question

Calculate the molality of the solution. ? An aqueous NaCl solution is made using 140g of NaCl diluted to a total solution volume of 1.00 L. Calculate the molality of the solution. (Assume a density of 1.08g/mL for the solution.)

Answer 1

Mass of water:

1.00 L = 1000 mL

D = m / V

1.08 = m / 1000

m = 1.08 x 1000 => 1080 g of H2O

Number of moles solute:

1 mole NaCl ---------- 58.44 g
?? moles NaCl ------- 140 g

140 x 1 / 58.44 => 2.3956  moles of NaCl

Solvent in kg: ( H2O)

1 kg --------- 1000 g
?? kg ---------1080 g

1080 x 1 / 1000 => 1.08 kg

molality = number of moles / solvent kg

m = 2.3956 / 1.08 kg

m = 2.218 mol/kg

hope this helps!