Hey there! So i\'ve been attempting this question for a while, and do not unders

Question

Hey there!

So i've been attempting this question for a while, and do not understand what I am doing wrong.

150 g of NaCl completely dissolves in 1.00 kg of water at 25.0 degrees C. The vapor pressure of pure water at this temperature is 23.8 torr. Determine the vapor pressure of the solution.

I know the equation is Pvap = XaPa (where X is the mole fraction of water = moles of water / moles of water + moles of solvent), and Pa is 23.8 torr, but when I use these numbers, I get 22.75 torr, while the answer is 21.8. Any help would be much appreciated! Thanks!  

Explanation / Answer

Raoult's Law can be used to express the vapor pressure relationships of solutions containing both volatile and nonvolatile solvents.
Raoult's Law is expressed by

Psolution = ?solventP0solvent

where

Psolution is the vapor pressure of the solution
?solvent is mole fraction of the solvent
P0solvent is the vapor pressure of the pure solvent

hence, Psolution = [55.55/(55.55+2.567)]*23.8=22.749tor ... so Ithink your ans is right

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