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Chemistry

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The vapor pressure of water at 25°C is 23.76 mm Hg. What would you calculate as the new vapor pressure of a solution made by adding 50.5 g of ethylene glycol (HOCH2CH2OH, antifreeze) to 50.5 g of water? You may assume that the vapor pressure of ethylene glycol at this temperature is negligible.

  • Chemistry -

    The first step to solve this equation is to calculate the moles of the solvent and solute.

    The molar mass of H2O=18.016 g/mol
    The molar mass of C2H6O2=62 g/mol

    50.5g of C2H6O2*(1mol/62g)=0.815 mol C2H6O2

    50.5 g of H2O*(1mol/18.016g)=2.803 mol H2O.

    Now you need to find the mole fraction of the solvent. Since H20 has more moles in the solution, it acts as the solvent.

    X=mol solvent/total mol
    X=2.803/3.618=0.775

    Now you can calculate the partial pressure of your solution
    Psoln=XH2O*PH2O
    Psoln=0.775*23.76=18.41 mmHg

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