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February 28, 2015

February 28, 2015

Posted by **Tommy** on Sunday, March 7, 2010 at 10:53pm.

1 L of an impure water solution has a freezing point of -11 °C. Which of the following is the

best estimate of the vapor pressure of the solution at 25 °C? Assume the vapor pressure of pure

water at 25oC = 23.76 atm, kF = 2 (K kg)/mol, and that water is 55 mol/L. Assume the density of

water is 1 g/mL.

- P. Chemistry -
**DrBob222**, Sunday, March 7, 2010 at 11:08pmdelta T = Kf*molality

11 = Kf*m

Calculate m

molality = moles/kg solvent.

I think we must assume 1 kg solvent although that won't be exactly right.

Calculate (estimate) # moles.

#moles + 55.5 for H2O = total moles.

Calculate mole fraction water,

Then vapor pressure H2O = mole fraction water x 23.76 BUT I don't think that is atm (It must be torr or mm Hg). This would be an estimate at best. Check my thinking.

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