[Mark S 2014]

I completed a distillation experiment the other day. The temperature plateaued at around 79°C, but the first drop of distillate occurred at 71°C. Just wondering what the significance of the first drop is. How can the liquid be boiling at 10°C under its boiling point ? (Liquid was cyclohexane Bp of 80.7°C).

[Mark S 2014]

In a distillation experiment the first liquid boiled at around 73°C, the second boiled at around 115°C. After the plateau in temperature at 79°C there was a drop in temperature , fractions where taken at 66,55,49,59,64,78°C before it rose again to around 115°C. The boiling points of the liquids where 80°C and 120°C. I do not understand how I was still getting distillate at these low temperatures. I would understand a drop in temperature with no distillate being produced between boiling points. I do not understand how I was still producing distillate (very slowly) at these temperatures. Any ideas of what was happening here ?

[Borek]

Light impurities should distill at lower temp, shouldn't they? Isn't it the point of distillation?

[Arkcon]

Well, its a little hard to follow your question, and you will have to explain it well in a write up, so we're all going to have to work with it.

If I follow you, you were collecting drops while the temperature was rising, and you expect only to collect during the two plateaus of the components.  Maybe that's conceptually correct, but a variety of other things may be happening.  Can you figure some of them out?

And I hope you don't mind that I've merged these two posts, they seem to be building on the same knowledge.

[Mark S 2014]

Sorry, its hard to explain the whole experiment in a short post. I've finished my lab report apart from a section that describes the unusual drop in temperature. I know a drop in temperature is sometimes accountable for by a lack of hot vapour at the still head due to the second component not boiling. But i was getting a substantial amount of distillate, indicating that either the first component was still boiling off, or the second less volatile component had started boiling. But how could either of these vapours be at such a low temperature ?