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Topic: Toluene and Water  (Read 5927 times)

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Offline AlphaScent

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Toluene and Water
« on: January 28, 2015, 03:43:54 PM »
So this is a question from my undergraduate organic lab that I am proctoring (teachers assistant) for the semester.  This question comes from there book and want to be sure I understand what is going on.  Some stuff it has been a while.

So,

A mixture of toluene (bp 110.8 C) and water is steam distilled.  Visual inspection of the distillate reveals that there is a greater volume of toluene than water present, yet water (bp: 100 C) has the higher vapor pressure. 
Explain the observation.

My thoughts:

It is too easy to say that it forms an azeotrope.  The chapter doesnt discuss azetropes.  Though the chapter before does.  I wasnt there last semester I do not know.  My thoughts are to just say that it does not conform to Raoults law and therefore the mole fraction does not matter.  It forms a constant boiling mixture.  It behaves as one compound.

What else is there to say/ Is there a better way to explain it?

This may be in the wrong spot.  MOd feel free to move it if it is.
If you're not part of the solution, then you're part of the precipitate

Offline TheUnassuming

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Re: Toluene and Water
« Reply #1 on: January 28, 2015, 05:54:37 PM »
Lit has the water/toluene azeotrope at ~80% by mass... so the azeotrope explanation is perhaps right in a way, just not detailed enough of an explanation? 
If they are covering Raoults law in this chapter the answer probably revolves around that.  I would just say that the toluene/water mix is not an ideal gas/liquid so the forces between the two liquids aren't uniform, making it possible for the mol fraction in the gas phase to be different than the liquid.  In the toluene/water case this gives the solution a positive deviation from Raoults law.  I don't know that there is really much else to say, especially for an undergrad organic lab. 
When in doubt, avoid the Stille coupling.

Offline AlphaScent

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Re: Toluene and Water
« Reply #2 on: January 29, 2015, 09:35:47 AM »
I am over thinking this I guess.  I wonder if any of them will even come up with azeotrope.

Thanks Unassuming

Cheers
If you're not part of the solution, then you're part of the precipitate

Offline TheUnassuming

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Re: Toluene and Water
« Reply #3 on: January 29, 2015, 03:04:04 PM »
I wonder if any of them will even come up with azeotrope.

haha... depends on the composition of the class.  Sophomore organic class I would expect a few of them to get it since there should be a few chem majors in there.
When in doubt, avoid the Stille coupling.

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