Question

the density of 3M solution of NaCl is 1.25g /ml. Calculate the molality of the solution ​

Answer 1

Given :

➳ Molarity of solution = 3M

➳ Density of solution = 1.25g/ml

To Find :

➳ Molality of solution.

SoluTion :

✭ Molarity : Number of moles of solute dissolved one litre of solution.

✭ Molality : Number of moles of solute per 1kg of the solvent.

Here, Molarity = 3M

Therefore,

◕ Moles of solute = 3

◕ Volume of solution = 1000ml

⇒ Mass = Density × volume

⇒ Mass = 1.25 × 1000

⇒ Mass = 1250g

➝ So, mass of solution = 1250g

➝ Now, we have to calculate mass of solvent to find molality of solution.

➝ Mass of solute = moles × molar mass = 3 × 58.5 = 175.5g

➛ solution = solvent + solute

➛ solvent = solution - solute

➛ solvent = 1250 - 175.5

➛ solvent = 1074.5g = 1.0745kg

▪ Molality = moles/mass of solvent

▪ Molality = 3/1.0745

▪ Molality = 2.79 moles/kg