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The vapor pressure if ethanol (C2H5OH) is 672 torr at 75°C. The vapor pressure of water...

The vapor pressure if ethanol (C2H5OH) is 672 torr at 75°C. The vapor pressure of water is 289 torr at the same temperature.
Calculate the mole fraction of ethonal and water in a solution that is 12% ethanol by volume.
Can any one help me step-by-step with this?

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Answer #1

P0EtOH = 672 torr P0H2O = 289 torr

From Roult's law for dillute solution,

P0EtOH = P soln × xEtOH and P0H2O = P soln ×xH2O here xH2O and xEtOH are the mole fraction of H2O and EtOH respectively.

so P0EtOH/P0H2O =xEtOH/xH2O =672/289 = 2.3526

xEtOH=2.3526× xH2O again xH2O + xEtOH = 1

therefore, xEtOH = 2.3526 × (1-xEtOH  ) =

so, (2.3526+1)xEtOH = 2.3526

3.526xEtOH =2.3526

xEtOH = 0.66

so xH2O = 1-0.66=0.34

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