Question

The density of 5 M solution of NaCl is 2.25 g/mol .Calculate the molality of the solution. Atomic masses of Na = 23u , Cl 35.5​

Answer 1

Answer:

Molar solution means there are 3 moles of NaCl salt in 1 Liter. Molecular weight of NaCl = 58.44.

Hence, there are 3×58.44 gms in 1 Litre of water.

Density =

volume

mass

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=1,074.68ml

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

=

1.07468

3

kg

=2.7915 Molal