Question

Calculate the molality and mol fraction for a 36% m/m HClsolution.

Answer 1

36% m/m means 36 g of HCl is present in 100 g of water
mass of HCl = 36 g
mass of water = 100 g
= 0.1 Kg
number of mole of HCl = (given mass of HCl)/(molar mass of HCl)
molar mass of HCl = 36.5 g/mol
number of mole of HCl = 36/36.5
= 0.99 mole

molality = (number of mole of HCl)/(mass of water in Kg)
= 0.99/0.1
= 9.9 m

number of mole of H2O = (given mass of H2O)/(molar mass of H2O)
molar mass of H2O = 18 g/mol
number of mole of H2O = 100/18
= 5.56 mole

mole fraction of HCl=(number of mole of HCl)/(number of mole of HCl+number of mole H2O)
mole fraction of HCl = 0.99/(0.99+5.56)
= 0.15

mole fraction of H2O = 1 - mole fraction of HCl
= 1-0.15
= 0.85