What is the mole fraction, 𝑋, of solute and the molality, 𝑚 (or 𝑏), for an aqueous solution that is 19.0% NaOH by mass?

Answer 1

19.0% NaOH by mass means 19 g NaOH / 100 g solution

If we have 100 g solution, the mass H2O = 100 g - 19 g = 81 g H2O = 0.081 kg

Moles NaOH = 19 g x 1 mol NaOH / 39.99 g = 0.475 moles

molality = 0.475 moles / 0.081 kg = 5.86 m

mole fraction NaOH = moles NaOH / total moles

moles H2O = 81 g H2O x 1 mol H2O / 18 g = 4.5 moles H2O

Total moles = 4.5 moles + 0.475 moles = 4.975 moles

Mole fraction (X) of NaOH = 0.475 mol / 4.975 moles = 0.0955