Question

Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is 0.040(assume the density of water to be one).

Answer 1

  As the given  moles OF ethanol = 0.040 
now will find water moles that will b
moles of water = 1 - 0.040=0.96 (substract 1 from etahnol mole fraction)
now the
mass of water = 0.96 mol x 18.02 g/mol=17.3 g  where 18 is atomic mass of water
mass of ethanol = 0.040 x 46 g/mol =1.84 g 
 now
mass of solution = 17.3 + 1.84=19.1 g  that is mass of water +mass of etanol
Now
assume that the density of the solution = 1g/mL 
so the
volume  ofsolution = 19.1 mL = 0.0191 L  
so finally the molarity will be
M = 0.040/ 0.0191=2.1
hope it helps