Question

the density of 3 molar solution of Nacl is 1.25g/ml calculate molality of the solution ??

Answer 1

Molarity = no. of moles of solute / volume of solution in L
Given, no. of moles of NaCl = 3
Density = Mass/ Volume
Mass of the solutuon = density x volume
 = 1.25 x 1000 = 1250 g
Mass of solute = mass of 3 moles of NaCl = 3 x (23 +35.5) = 175.5 g
∴ mass of solvent = mass of solution - mass of solute
 = 1250 - 175.5 = 1074.5 g =1.074 kg
∴ molality = no. of moles of solute/ mass of solvent = 3/1.074 = 2.79

∴ molarity = (molality x density x 1000 )- molar mass /1000
 = (2.79 x 1.25 x 1000) - 58.5 /1000 = 3.4M