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When 9.18 g of a soluble nonelectrolyte was dissolved in 100 g of ethanol at 78.4°C, the vapor pressure of the solution was measured to be 740 mm Hg.
What are the mole fractions of ethanol and solute?
What is the molecular weight of the solute?

  • Chemistry -

    I don't know the vapor pressure of ethanol at 78.4 C but you can look that up. I will assume it is 760 mm since I know that is close to the boiling point of ethanol.
    Psoln = Xsolvent*Posolvent
    Solve for Xsolvent.
    Then 1-Xsolvent = Xsolute which is part a.

    Then Xsolute = (moles solute/moles solute + moles solvent).
    You know moles solvent = 100 g/molar mass ethanol. Substitute into the Xsolute equation above and solve for moles solute.
    Then n(solute) = grams solute/molar mass
    You have n and g, solve for molar mass, which is part b.

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