We have to calculate the mole fraction of ethanol in the vapor above solution.

The mole fraction of a component in the vapors above the solution is calculated using this formula:

$\overline{){{\mathbf{X}}}_{{\mathbf{a}}}{\mathbf{}}{\mathbf{=}}{\mathbf{}}\frac{{\mathbf{P}}_{\mathbf{a}}}{{\mathbf{P}}_{\mathbf{t}}}}$

**Where,**

X_{a} = mole fraction of a component in vapors above solution

P_{a} = vapor pressure of a component of solution

P_{t} = total vapor pressure

At 63.5^{o}C the vapor pressure of H_{2}O is 175 torr, and that of ethanol (C_{2}H_{5}OH) is 400 torr. A solution is made by mixing equal masses of H_{2}O and C_{2}H_{5}OH.

What is the mole fraction of ethanol in the vapor above the solution?

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