Question

Density of 3m solution of nacl is 1.25g/ml. Calculate the molality of solution

Answer 1

Molarity = no. of moles of solute / volume of solution in L

Given, no. of moles of NaCl = 3

Density = Mass/ Volume

Mass of the solution = density x volume

 = 1.25 x 1000 = 1250 g

Mass of solute = mass of 3 moles of NaCl = 3 x (23 +35.5) = 175.5 g

∴ mass of solvent = mass of solution - mass of solute

 = 1250 - 175.5 = 1074.5 g =1.074 kg

∴ molality = no. of moles of solute/ mass of solvent = 3/1.074 = 2.79

∴ molarity = (molality x density x 1000 )- molar mass /1000

 = (2.79 x 1.25 x 1000) - 58.5 /1000 = 3.4M