Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: AlphaScent on January 28, 2015, 03:43:54 PM
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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.
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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.
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I am over thinking this I guess. I wonder if any of them will even come up with azeotrope.
Thanks Unassuming
Cheers
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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.