Question

What is the mole fraction, X, of solute and the molality, m (or b), for an aqueous solution that is 13.0% NaOH by mass?

Answer 1

NaOH = 13 g

water mass = 87 g

molality = (mass of solute / molar mass) x (1000 / mass of solvent)

              = (13 / 40) x (1000 / 87)

             = 3.74 m

molality = 3.74 m

moles of solute = 13 / 40 = 0.325 = n1

moles of solvent = 87 /18 = 4.83 = n2

total moles = 5.16

mole fraction of solute = n1 / total moles = 0.325 / 5.16

                                    = 0.063