[BigJ9595]

The question is: A solution of NaCl in water has a vapor pressure of 20.7 torr at 25 deg. C.  what is the mole fraction of NaCl in this soultion?

I did tihs:
20.7 = (x) 23.8, solved for x, did 1 - x to get the mole fraction of solute not solvent, then divided by 2 becasue NaCL dissociates so the mole fraction of NaCl is half that of what it appears to be in the solution.

However, my answer is wrong so clearly something i just said is not right, and i have no idea which part.
Thanks

[BigJ9595]

The process i used turns out to be right, the problem was that the website i was submitting it to was using a differnt constant than we were given in the book.  

Sorry for any confusion.

[rhino928]

I am having trouble figuring out how to even get started on this problem.  I'm sure it's not as tough as I am making it out to be but here it is.

The following compounds, listed with their boiling points, are liquid @ -10 degrees C:  butane, -0.5 degrees C; ethanol, 78.3 degrees C; tolulene, 110.6 degrees C.  At -10 degrees C, which of these liquids would you expect to have the highest vapor pressure?  Which the lowest?  Explain.

Any help that can at least get me started in the right direction here would be greatly appreciated.

Thx,
Rhino

[Borek]

What is definition of boiling? How does boling relate to vapor pressure? How does vapor pressure changes with temperature?

Edit: Oh man, don't reuse old threads, post in a new one!

[sdekivit]

The question is: A solution of NaCl in water has a vapor pressure of 20.7 torr at 25 deg. C.  what is the mole fraction of NaCl in this soultion?

I did tihs:
20.7 = (x) 23.8, solved for x, did 1 - x to get the mole fraction of solute not solvent, then divided by 2 becasue NaCL dissociates so the mole fraction of NaCl is half that of what it appears to be in the solution.

However, my answer is wrong so clearly something i just said is not right, and i have no idea which part.
Thanks

your approach on this problem is correct though and i get the same answer as you.