[Sheryl]

Why does the boiling point of a two-component mixture rise slowly throughout a simple distillation when the boiling point differences are not large?

I've never done a simple distillation and can't find the info in the book so I haven't the foggiest.

Thanks from Sheryl

[Bakegaku]

Hmm.... is there a specific situation you're talking about?  I suppose if the still isn't properly ventilated then an increase in pressure would cause higher poiling points.

[Yggdrasil]

Well, what is the point of a distillation?  What happens to the relative amount of the two components in your flask as teh distillation proceeds?

[Sheryl]

The component with the lower b.p. boils off and I would expect the temperature to rise rapidly.  A simple distillation is done when there is a large difference in temps.

Ths question is a general question.  No specifics were given other that what I wrote.

Sheryl

[Yggdrasil]

The component with the lower b.p. boils off and I would expect the temperature to rise rapidly.

Exactly, as the distillation proceeds, the lower b.p. component boils off, enriching the liquid phase in the higher boiling component.  Since the liquid phase now has a higher mole fraction of the higher b.p. component, its boiling point is now higher.

Look up Raoult's law and two-component phase diagrams for more information.  The following site may also be helpful:

http://www.chem.arizona.edu/~salzmanr/480a/480ants/vpdiag&/vpdiag&.html

[Sheryl]

Very helpful.  Thanks very much.

Sheryl