Question

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

Answer 1

Final Answer: 2.8mol/kg

Let there be 1L solution.
For 3M solution of NaCl, 3 moles of NaCl in 1 L solution.
By using the density, we can find out the mass of the 1L of solution.
Mass of solution = Volume * Density
= 1000 * 1.25
= 1250g

Mass of solute = mass of 3 moles of NaCl
= 58.5* 3
= 175.5g

Mass of solvent= Mass of solution - mass of solute = 1250-175.5
= 1074.5g

Morality, m = moles of solute / mass of solvent (in kg)
= 3/(1074/1000)
= 3000/1074.= 2.8mol/kg