[thenuttyprofessor]

For a minimum boiling point azeotrope, if the composition of a mixture is higher than the azeotrope composition, does that mean a pure component will boil off first until it's at the same composition of the azeotrope?

For example:

Azeotrope - benzene 60% methanol 40% boils @ 58.3 degrees

Mixture - 90% methanol (b.p. 80 degrees) 10% benzene (b.p. 64.5 degrees)

When the mixture is distilled will pure methanol distill first until the mixture composition is 40% methanol 60% benzene?  In my book and according to my notes in a minimum b.p. azeotrope the azeotrope leaves first then the pure substance leaves.  Are they trying to simplify this or am I missing something here?  Also, if the methanol boils off first then will it boil off at 80 degrees or 58.3 degrees.

Thank you.

[movies]

You've got your bps backwards.  Methanol boils at 65 degrees C and benzene at 80 degrees C.

[wainblatrobert]

Yes Nuttyproff you were correct in your asumptions, until the azeotrope proportions are reached each compound will boil at their boiling points....so in your case methanol will boil first until it becomes 40% of the mixture after that you'd have to use other methods of separation.