Question

what is the mole fraction of a solute and the molal concentration for an aqueous solution that is 17.0% NaOH by mass?

Answer 1

Molality definition is moles of solute by kilogram of solvent. n solute/mass solvent
Mole fraction is equal to moles of solute by total number of moles (solute + solvent)
17.0% NaOH means 17g of NaOH in 100g of solution or 17g NaOH + 83 g H20

1) With the % concentration you can calculate the grams of NaOH per 1000g of water

1000g H2O x 17.00g NaOH/ 83.00g H2O = g of NaOH/kg solvent

2) then convert this g of NaOH/kg solvent to moles of NaOH (nNaOH=mNaOH/MMNaOH) and you will have the molality of the solution.

3) to calculate the molar fraction you have to calculate the number of moles of H2O in 1000g of H20 (nH2O=mH2O/MMH2O)
Then Molar fraction = moles of NaOH/Total Moles= Molality/(molality+nH2O)