# Vapor pressure of pure water

1. Oct 18, 2005

### amcavoy

$$X_1=\frac{n_1}{n_1+n_2}\implies n_2=\frac{n_1-X_1n_1}{X_1}$$

where n1 is the moles of solvent and n2 is the moles of solute.

$$22.98=X_1\left(23.76\right)\implies X_1=.9672$$

and 1000 g of water is equal to 55.49 mol (n1), so plugging this all in gives:

$$n_2=1.88\text{mol}$$

which would be the same as the molarity.

However, my textbook says that the molarity is .920 m. Where did I go wrong? Thanks a lot.

2. Oct 19, 2005

### Staff: Mentor

NaCl is dissolved.

3. Oct 23, 2005

### amcavoy

Right, Na++Cl-->NaCl.

Thanks for the help.

4. Sep 30, 2009

### bellanovela

Re: Molality

Can someone please explain this to me, because I'm not quite sure how to solve this problem. I only reached the part where I got the mole fraction of water and NaCl, but that's just it. I don't know what to do next. Help would be greatly appreciated. :(

5. Sep 30, 2009

### Staff: Mentor

Re: Molality

You mean you have no idea how to convert molar fraction to molality?

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6. Oct 1, 2009

### bellanovela

Re: Molality

Okay, I found out how to convert it molality, but I keep getting 1.88 m not .920 m. How does the strong electrolyte/complete ionization of NaCl make a difference?

Last edited: Oct 1, 2009
7. Oct 1, 2009

### Staff: Mentor

Re: Molality

Check what Van't Hoff factor is.

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