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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Brian Lin on December 27, 2013, 10:17:07 PM

Title: Solution/ Vapor Pressure Question
Post by: Brian Lin on December 27, 2013, 10:17:07 PM
Here it is:
(BTW, it's harder than it looks)

You have a solution of two volatile liquids, A and B (assume ideal behavior). Pure liquid A has a vapor of 350.0 torr and pure liquid B has a vapor pressure of 100.0 torr at the temperature of the solution. The vapor at equilibrium above the solution has double the mole fraction of substance A that the solution does. What is the mole fraction of liquid A in the solution?

I used V sup as vapor state and L has solution (liquid state). The o sup means "pure solvent by itself"

Since both of the liquids are VOLATILE, I used the altered Raoult's Law equation.
Ptotal= XaL*Pao +  XbL*Pbo

_______________________________________

I cleaned up the messy work and reorganized it.

I didn't want to type it all above due to all the superscripts, so I took a picture.

Title: Re: Solution/ Vapor Pressure Question
Post by: Brian Lin on December 27, 2013, 10:23:07 PM

P(total)= Pa+ Pb

X(aL) + X(bL)=1

X(aV) + X(bV)= 1

Clue they gave you:

X(aV)= 2X(aL)
Title: Re: Solution/ Vapor Pressure Question
Post by: Borek on December 28, 2013, 04:03:10 AM
There are several good points in what you wrote, but it is way too chaotic for me.

Please list separately all unknowns and all equations, if there are as many equations as unknowns, you are done (the rest is a simple math), if not - you need to look for additional dependences.
Title: Re: Solution/ Vapor Pressure Question
Post by: Brian Lin on December 29, 2013, 01:05:08 AM
Borek, how do I reattach a new PDF? All the sub and superscripts typed online looks really messy, so is it possible to remove this PDF? (I will write neater, I promise)
Title: Re: Solution/ Vapor Pressure Question
Post by: Borek on December 29, 2013, 03:36:24 AM
Why don't you post using LaTeX?

http://www.chemicalforums.com/index.php?topic=59314.0