The density of 3M solution of NaCl is 1.25 g/mL. Calculate molality of the solution.

3 Molar solution means there are 3 moles of Na Cl salt in 1 Liter.

Molecular weight of Na Cl = 58.44. Hence, there are 3 * 58.44 gms in 1 Litre of water.

Density = mass/volume

Mass of 1 litre of solution = 1.25 gms/ml * 1000 ml = 1, 250 gms

V = volume of water added to make the solution or volume of solvent

Mass of solute + Mass of solvent = Mass of solution

175.32 gms + mass of solvent = 1, 250 gm

mass of solvent = 1250-175.32 = 1074.8

So 1, 074.68 gms of water is mixed with 3 moles of NaCl to make the 3 M solution.

Molality = mass of solute in number of moles / mass of solvent in kg
= 3 / 1.074.8 kg
= 2.7915 Molal

Answer : Molality = 2.79 molal