[jmarjorie]

Dear All,



This goes out to those expert in fractional distillation : A mixture contains 2 organic liquids (completely miscible with each other), one with a boiling point of 80 deg C and the other with a boiling point of
35 deg C.

Can the two liquids be completely seperated by fractional distillation using a very long column or will they behave as a binary azeotropic mixture at constant pressure (constant boiling point mixture) and the distillate still contain proportions of both mixtures ?

I'am asking as I have not fully understood the concept; some say the mixtures are not seperable while others say the mixtures are completely seperable; am confused.

[AWK]

For deciding on possibility of separation you should know content of solution. From the data you showed I can assume that your mixture contains ethyl ether and ethanol. Iin this case complete separation is impossible since both compoundsl form azeotrope with minimal boiling point 34.20 C with 1.2 % (w/w) content of water.

[mir]

Why do we have azeotropic mixtures?

Is it something thermodynamic?

[Borek]

All depends on the interactions between particles of substances present in the solution (more precisely - on their relative strengths).

[beheada]

Question:
If you have an azeotropic mixture, but you have a say 60% ethanol, 40% water (or substitute azeotropic mixture here), will the mixture boil at the azeotropic bp until all of the water has been distilled then leave what's left of the ethanol in the boiling flask? Shouldn't the boiling point jump up to the actual bp of ethanol after the water content is removed?

[AWK]

In this case, since azeotrope has the lowest boiling point (compared to alcohol and water), you can remove all azeotrope from the mixture

[beheada]

So if there are only two components, i.e. ethanol and water, and you remove all azeotrope from the mixture, doesn't that leave you with only one or the other?

This is the part I'm not understanding. If you have any ethanol or water left in the mixture, then it will form an azeotrope, right? If that's the case, you have to distill out the azeotrope, leaving only the higher volume of the two in the mixture left? Is that right?

Or is the only way to get one or the other to add something like benzene in order to form an even lower-boiling point azeotrope?

[AWK]

http://www.westga.edu/~chem/courses/chem410/3510_04/sld036.htm
http://www.westga.edu/~chem/courses/chem410/3510_04/sld037.htm
http://www.westga.edu/~chem/courses/chem410/3510_04/sld038.htm