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x_coh_x
x_coh_x asked in Science & MathematicsChemistry · 1 decade ago

Finding the mole fraction (using vapor pressure)?

A solution contains a mixture of pentane and hexane at room temperature. The solution has a vapor pressure of 259 torr . Pure pentane and hexane have vapor pressures of 425 torr and 151 torr , respectively, at room temperature.

What is the mole fraction of hexane? (Assume ideal behavior.)

I tried solving this several ways, but not even my book gives me any information about how to find mole fractions from vapor pressure.

Please explain!!

2 Answers

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  • Dr.A
    Lv 7
    1 decade ago
    Favorite Answer

    p ( hexane )= 151 X ( hexane)

    X = mole fraction hexane = moles hexane / moles hexane + moles pentane)

    Let Y = mole fraction pentane = moles pentane / moles hexane + moles pentane

    X + Y= 1

    Y = 1 - X

    p ( pentane ) = Y x 425 = ( 1- X ) x 425 = 425 - 425 X

    259 = p ( pentane ) + p ( hexane) = 151 X + 425 - 425 X = - 274 X + 425

    - 166 = - 274 X

    X = 0.606

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