[Siro]

I have done a lot of research but lacking actual experience in doing so, I am stuck with one question that I can't seem to find the answer to..

The temperature. Where do I measure it? Do I have the thermometer at the top of the column right near the condenser entry?

Hypothetically say I have a mixture of 3 liquids that I want to distill out. They evaporate/boil at 96,118, and 153, respectively. How exactly do I go about collecting each fraction? How do I go about calibrating/heating specifically towards each temperature to collect the purest distillation of each liquid? Would I just crank the hot plate up, with a stirrir, and then will the temperature at the top of the column automatically be those specific boiling temperatures depending on the substance, starting with the lowest? Or is there a more specific/detailed careful manner of doing this?

From the texts I have read, mostly they've all seemed to say, heat up the mixture, and only collect the fraction when it is at your target temperature, when it changes, that means something else is evaporating. Is this assuming a constant source of heat, because otherwise is not stated?

Perhaps I'm a little foggy on boiling science. If a mixture is heated up, with a constant energy input through the entire distillation, with a fractionating column, do the liquids/solvents evaporate out one at a time with (mostly) the lowest temperature going first? Like do these low boiling molecules steal energy from the higher boiling molecules, and as a result leave before they do, at least in greater ratios? Something as simple as this should not be this hard for me to wrap my head around.

Any help/pointers is appreciated!

[Arkcon]

From the dozens of questions in your missive, I can only pull out one underlying theme -- you have no idea of what to really ask.  Lets start with the Wikipedia page:  http://en.wikipedia.org/wiki/Distillation#Laboratory_scale_distillation  I've gone and highlighted the laboratory scale section, but there truly isn't a single part of that page that you shouldn't read -- yes, even the industrial distillation for petroleum refining, its all very important to pull the information together.  Briefly however, fractional distillation requires a fractionating column between the still pot and the condenser: http://en.wikipedia.org/wiki/Fractional_distillation

[Siro]

Thank you for the links, I will look over them once more.

I have about $3000 worth of glassware, whatever I will need for any procedure, at least most of them. Some people might disagree with my approach of buying a ton of lab-glass before having an indepth knowledge, but I thoroughly intend to master the subject over time so I might as well have it to practice. I have a whole semester or 2 before my first organic chem class and I'm just too passionate about the subject to wait.

I don't see anywhere on those links information regarding thermometer placement in the column. I've seen set ups with it near the condenser joint, as well as set ups with it halfway down the column. Logic tells me you would want it partially down the column so when the temperature changes, you can remove the receiving flask before other solvents go over? Having it near the joint seems to run the risk of the receiving flask getting contaminated if it is not removed quickly enough.

I guess the original post could have been simplified to 2 questions: Where should the thermometer be placed in the column, and why? Regarding Volatility, regardless of heat input, will the most volatile molecules have first priority in receiving energy and always evaporate before the less volatile molecules(at least in a greater ratio)? I just found http://en.wikipedia.org/wiki/Relative_volatility, and I will be reading over that... but all input would still be greatly appreciated.

[Arkcon]

There thermometer goes where it was drawn on the image in the fractional distillation Wikipedia page   That is, at the top of the fractionating column, where vapor would go into the condenser.  You measure the temperature of the vapor that is making it out of the fractionating column.  Because that is what's condensing.  To answer other questions you asked, yes, some higher boiling vapors may leave the pot, and re-condense on the fractionating column, while other vapors make it past.  That is the purpose of the fractionating column, and is a phenomena referenced multiple times on those pages, for example: http://en.wikipedia.org/wiki/Distillation#Industrial_distillation

[Siro]

Thank you for the swift response, and Yup ^.^. I totally understand the purpose of the fractionating column, though I don't think I am being clear enough with my question. Say I am distilling something at 70 degrees, with another liquid that is 100 degrees. The moment the thermometer starts rising up, that means that some of the other liquid/solvent has already entered the condenser and is now on it's way to polluting my distillation. If the thermometer is effectively measuring what is currently at the condenser inlet, then by the time I see it rising, is it not too late? The rising would imply there is a different substance at the condenser inlet, or rather an increasing quantity of it. So how do we get around this minuscule pollution of the distillate without doing another distillation that we simply stop before it gets dry?

What I'm talking about here is maybe 1 or 2 ml of pollution, but still an impure sample is an impure sample.

[Arkcon]

I was always able to switch receiving flask in time, based on when the temperature changed.    And a single drop contamination isn't really the end of the world, so long as the collected volume is large enough.  If the liquids have very different properties, you can see that droplet condensing and dripping down the condenser before it leaves -- that's hard to describe, you'll have to see it for yourself.

[Siro]

Yes I do suppose a lot comes from experience. I guess I will just wait and see ^.^