The density of 3 M solution of NaCl is 1.25 g mL-1. Calculate molality of the solution. NCERT Class XII Chemistry - Main Course Book I Chapter 1. Some Basic Conpepts of Chemistry

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by premRaman

2015-05-30T16:34:55+05:30

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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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