Question

An aqueous solution contains 4.5 % NaCl by mass. calculate molality. calculate mole fraction

Answer 1

4.5% NaCl by Mass means 4.5 g of NaCl in 100 g of solution. (mass of solvent = 100 - 4.5 = 95.5 g)

molality = (mass/molarmass)*(1000/mass of solvent in g)

              = (4.5/58.5)*(1000/95.5)

              = 0.805 m

moles of NaCl = 4.5/58.5 = 0.0769

moles of water = 95.5/18 = 5.305

molefraction of NaCl = moles of NaCl/total moles = 0.0769/(0.0769+5.305) = 0.0143

molefraction of water = 1- 0.0143 = 0.9857