Question

the density of 3M solution of nacl is 1.25g per mole . calculate molality of the solution

Answer 1

In the question density should be “1.25 g/ml”

Molarity = 3 M
It means 3 moles of solute is present in 1 litre solution (= 1000 ml)

Mass of solution = Density of solution × Volume of solution
= 1.25 g/ml × 1000 ml
= 1250 g

Mass of solute = Moles of solute × Molecular mass of solute
= 3 mol × 58.44 g/mol
= 175.32 g

Mass of solvent = Mass of solution - Mass of solute
= 1250 g - 175.32 g
= 1074.68 g
= 1.07468 kg

Molality = Moles of solute / Mass of solvent in kg
= 3 moles / (1.07468 kg)
= 2.78 m
≈ 2.8 m

Molality of solution is 2.8 m