EK Gen Chem Question

[nanaschool2000]

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1001 Questions Book #519

A solution of ethanol and water is slighly nonideal; the water-ethanol attractions, in particular, are stronger than the ethanol-ethanol attractions. This results in a lowering of the vapor pressure of the alcohol in the mixture beyond what is predicted by Raoult's law. Suppose a scientist measures the vapor pressure of ethanol above an ethanol-water mixture, and then uses Raoult's law to estimate the mole fraction of ethanol in the mixture. How is the estimate affected by the deviation from ideality?


Answer is a) The estimate is too low


I don't really understand. Can some explain?

 

[Seraph 84]

The ethanol vapor pressure that the scientist measured is slightly lower than what we would expect for an ideal ethanol-water mixture. When he uses Raoult's Law to estimate the mole fraction of ethanol, it will be lower because the vapor pressure of ethanol was lower.