# Vapor Pressures of Solutions

1. Feb 3, 2004

### Integral0

Here is the question:

A solution of sodium chloride in water has a vapor pressure of 19.6 torr at 25 degrees celsius. What is the mole fraction of NaCl in this solution? The vapor pressure of pure water is 23.8 torr at 25 degrees celsius.
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Here's what I need help with:

I am able to determine the mole fraction for H20 = .824
because I took Psoln = XsolventP^0solvent (Raoult's Law) and then I did this

Psoln divided by P^0solvent to get Xsolvent (kie solvent(mole fraction of solvent or H20)).

I got .824 for the mole fraction of H20 but now I am unsure about how to find the mole fraction of the solute (NaCl).

HOW DO YOU FIND THE MOLE FRACTION OF THE SOLUTE?

Thanks

2. Feb 3, 2004

### GCT

1 - mole fraction of water = mole fraction of solute.

Last edited: Feb 3, 2004
3. Feb 3, 2004

### Integral0

RE;

How did you formulate this, GeneralChemtutor?

Does that mean .824 H20 solvent = .824 NaCl solute?

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If this is true . . . doesn't it need to be 2(.824)? B/c ionic solute's dissolve . . . like this -> NaCl -> 1 mol Na + 1 mol Cl ??

Last edited: Feb 3, 2004
4. Feb 3, 2004