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10 December, 20:07

A solution of benzene and toluene at 25 °C exerts a total vapor pressure of 66.6 torr. What is the mole fraction of benzene in the vapor phase? The vapor pressures of pure benzene and toluene at 25 °C are 94.2 torr and 28.4 torr, respectively. 0

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  1. 10 December, 20:18
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    0.5805.

    Explanation:

    Using Raoult's Law;

    Psol = Xbenzene * P°benzene + Xtoluene * P°toluene

    where,

    Psol = vapor pressure of the solution

    Xbenzene = mole fraction of benzene

    P°benzene = vapor pressure of pure benzene

    Xtoluene = mole fraction of toluene

    P°toluene = vapor pressure of pure toluene

    Mole fraction is defined as the ratio between the number of moles of a component in a solution to the total number of moles in the solution.

    Xbenzene + Xtoluene = 1

    Let,

    Y = mole fraction of toluene

    X = mole fraction of benzene

    X = 1 - Y

    Psol = X * P°benzene + (1 - X) * P°toluene

    66.6 = X * 94.2 + (1 - X) * 28.4

    X = 0.5805

    Therefore,

    Y = 1 - 0.5805

    = 0.4195

    Mole fraction of benzene = 0.5805.
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