akimhaneul

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For Azeotropes I know that it is a mixture that cannot change its component percentage because the vapor composition and liquid compositions are same. Why does this happen? Why stop at certain point?





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sazerac

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If you look up azeotropes on Wikipedia, the Mechanism section explains it pretty well.

If water sticks to water well, and ethanol sticks to ethanol well, but water sticks to ethanol just so-so, then you will have a positive deviation from Raoult's law and the boiling point of the azeotrope ethanol-water will have a lower boiling point than either water or ethanol and the azeotrope will boil off first.
 
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aldol16

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It's all about relative A-A, B-B, and A-B interactions. I believe this is beyond the scope of the MCAT - if it's on there, it's very low-yield material because people generally don't cover azeotropes at any depth in gen chem.
 
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sazerac

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It's all about relative A-A, B-B, and A-B interactions. I believe this is beyond the scope of the MCAT - if it's on there, it's very low-yield material because people generally don't cover azeotropes at any depth in gen chem.
Isn't it an OChem concept though? Distillations and all that? I could totally see a distillation passage with a few related questions.
 

aldol16

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Isn't it an OChem concept though? Distillations and all that? I could totally see a distillation passage with a few related questions.

It's not so much of an OChem concept - it's not taught in most introductory organic chemistry courses. In most cases, it's not taught at any measurable depth until a PChem course. In any case, I highly doubt it would come up in a distillation question and even if it could, it is extremely low yield.
 
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