The partial pressure of water above a solution of water and a nonvolatile solute at 25oC is 18.6 mm Hg. What is the mole fraction of the solute?

2 answers

According to Raoult's Law,
Psolution = XsolventPsolvent
18.6mmHg = X(H2O)*P(H2O at 25o)

Look up the water vapor pressure at 25, substitute above, and solve for X(H2O).
18.6mmHg = X(H2O) * 23.76mmHg
X(H2O) = .7838

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