What is the mole fraction?
Answer:
Raoult's Law: P solution = XsolutePsolute + XsolventPsolvent
Xethanol = 5/10 = 0.5, Xwater = 0.5
Psolution = 0.5(43.6 Torr) + 0.5(17.5 Torr)
Psolution = 21.8 Torr + 8.75 Torr = 30.6 Torr (sig figs)
Now, Psolute/Psolution = Xsolute in gas phase.
21.8 Torr/30.6 Torr = 0.712 (Notice that in the gas phase the solute, in this case ethanol, has a higher mole fraction, the vapor is richer in ethanol). This allows for distillation. If you repeat the condensing, evaporation, condensing, evaporation cycle, in principle is possible to distill pure ethanol from water. Unfortunately, an azeotrope (a mixture that cannot be separated any further), consisting of 95% ethanol and 5% water forms, so that is the maximum purity of ethanol distilled from water, to remove the remaining 5% of water, chemical removal of water has to be done, to get 100% ethanol, which is possible.
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