# The first vapor collected from a fractional distillation (BP's listed)

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#### csx

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The temp of the thermometer reads 50 degrees as the first aliquot is collected.
which is the identity? I will just list the BP's given rather than comp names
A) 60 deg
B) 100 deg
C) 36 deg
D) 48 deg

the answer was D. Why is the answer not C. Should that not be the first to come out?? Answer key doesnt explain why its not C.

I really dont understand why D is the first aliquot collected.

@csx

This is a guess but perhaps in this experiment you are gradually heating up until 50 degrees. So maybe by the time you reach 50 degrees, the 36 degree stuff has mostly evaporated?

@csx

This is a guess but perhaps in this experiment you are gradually heating up until 50 degrees. So maybe by the time you reach 50 degrees, the 36 degree stuff has mostly evaporated?
The fact that the question said the first aliquot collected would make me say otherwise though! So gradual or not, its the first (in my opinion). this is confusing.

@csx

If I had to answer the question myself, I would have chosen what you did too.

Perhaps you don't collect the stuff in the beginning (as in, treat the thing with 36 degree BP as an impurity you want to get rid of). I know that's stretching it but I'm trying to rationalize it lol.

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Anyone else wanna chime in and be the hero???

I was going to say this, and I really would have chosen what you did too. But I have noticed this trend where you gotta be right above or below the value you are looking for.

So for example, if your thermometer reads 50 degrees, you should assume that your aliquot of 36 degree bp was collected at 38 degrees and now your 48 aliquot is being collected at 50 degrees. Those are my thoughts, you always want to be slightly above the BP.

If you were at 50 degrees to collect the aliquot then how can you differentiate between something that had a 36bp and 48bp? you can't you would get a mixture. That is just my thought... not trying to be a hero...I will gladly accept the title tho

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I am thinking it is because "as the first aliquot is collected" means something like "the first substance to condense after attaching the collection beaker after 50 degrees has been reached." So they only start collecting after 50, the first substance would be the one with a bp of 48 presumably... Weird question though.