Question

Liquid vapor phase diagram

If you have a 99% of ethanol (in more fraction) and plan to mix it with water, how would calculate how much volume of water needed to satisfy the mole composition? Assume the given ethanol volume is 100 mL.

Answer 1

if volume oethanol is = 100 mL

then.. the solution will be pretty dilute with respect to solvent

so assume Volumes ARE additive

so...

for a 99% mole fraction

mass of 100 mL = D*V

density of ethanol = 0.789 g/mL

so

mass = 0.789*100 = 78.9 g of ethanol

Mw of ethanol = 46 g/mol

mol = mass/MW = 78.9/46 = 1.715217 mol

so...

for a 0.99 of ethano...

we require...

total mol = 1.715217/0.99 = 1.7325 mol of mix

so..

mol of water = 1.7325*0.01 = 0.017325 mol of water

mass of water = mol*MW = 0.017325*18 = 0.31185 g of water

so...

volume of water = 0.31185 g/ 1g/mL = 0.31185 mL required