Why can an azeotrope form when a solution has a higher boiling point than..

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Why can an azeotrope form when a solution has a higher boiling point than the pure substances that make it?

According to EK:

"An azeotrope can also form when the solition has a higher boiling point than either pure substance."

I understand why a low boiling azeotrope cannot be distilled. But, if the boiling point of the azeotrope is say 150°C, and the components boiling points are 70 and 100°C, why wouldn't the first component vaporize at 70°C?

Thanks

 

[thebillsfan]

well, it's like saying sodium has a BP of 50, chloride has a bp of 70, but nacl has a bp of 100. it's almost like a different compound, distinct from its components. i think...at least, thats a good way to think about it even if its not technically correct
hth

 

[ratatat]

Hey, yeah I guess that's not the most scientific explanation, but I guess that is a good way to think of it. Thanks 😀