Question

A solution of isopropyl alcohol, C₃O₇OH, in water has a mole fraction of alcohol equal to 0.42. what is the weight per cent alcoholand te molarity of the solution?

Answer 1

mole fraction of alchol = (number of mole of alchol)/(total number of mole)
if, number of mole of alchol = 0.42 mole
then, total number of mole = 1
number of mole of water = 1-0.42 mole
= 0.58 mole

molar mass of C3H7OH = 60 g/mol
mass of C3H7OH = (number of mole C3H7OH)*(molar mass of C3H7OH)
= 0.42*60
= 25.2 g
molar mass of water = 18 g/mol
mass of H2O = (number of mole H2O)*(molar mass of H2O)
= 0.58*18
= 10.4 g

mass% of alchol = {(mass of alchol)/(total mass)}*100
= {25.2/(25.2+10.4)}*100
= 70.8%

molarity = (x*d*10)/M
x = mass% of alchol
d = density of solution
= density of water
= 1 g/mL
M = molar mass of C3H7OH
= 60 g/mol
so,
molarity = (70.8*1*10)/60
= 11.8 M