The density of 3 M solution of NaCl is 1.25 g mL^-1. Calculate molality of the solution

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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

175.32 gms + 1 gm /ml * V = 1, 250 gm
=> V = 1, 074.68 ml

So 1,074.68 ml or 1, 074.68 gms of water is mixed with 3 moles of Na Cl to make the 3 M solution.

Molality =

mass of solute in number of moles / mass of solvent in kg
= 3 / 1.07468 kg
= 2.7915 Molal

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