[curiouscat]

Most binary azeotropes I can think of have an azeotropic-BP pretty close to the BP of at least one component. By pretty close, say, ~10-20%. Firstly, is my observation valid? Or not?

Browsing Wikipedia's table of azeotropes I came across one that seems a bit of an exception:

Perchloric acid (pure BP 110°C) is listed having an azeotrope with H₂O that boils at 203°C. This BP is about twice either component's BP(100 / 110). Is there an error here or this is truly an exception?

http://en.wikipedia.org/wiki/Azeotrope_(data)

Or are there other such pairs?

[tomek]

You can encounter many more examples like that. For instance HCl (bp -85 °C) and water (bp 100 °C) will distill as an azeotrope (circa 20% HCl depending on external pressure). This is known as constant-boiling hydrochloric acid and has been recommended as a standard for acidimetry-alkalimetry.

[curiouscat]

You can encounter many more examples like that. For instance HCl (bp -85 °C) and water (bp 100 °C) will distill as an azeotrope (circa 20% HCl depending on external pressure). This is known as constant-boiling hydrochloric acid and has been recommended as a standard for acidimetry-alkalimetry.

That doesn't sound like what I was talking about.

Const. boiling HCl boils at ~110°C, correct? That's only 10% off BP of H2O.

The example I quoted was weird because 203°C is so far off from both 100°C and 110°C. I'm finding it hard to believe that much of non-ideality could exist.

[Wastrel]

When you read "azeotrope" think "compound".  If you distill a mixture of HCl and NH3 you'll find a proportion forms a high boiling solid that cannot be seperated by distillation.  Likewise when you read "non ideality" in this context think "chemical bonding".

[curiouscat]

When you read "azeotrope" think "compound".  If you distill a mixture of HCl and NH3 you'll find a proportion forms a high boiling solid that cannot be seperated by distillation.  Likewise when you read "non ideality" in this context think "chemical bonding".

You mean for all azeotropes or specifically ones which boil at T way different from either component?

[tomek]

that doesn't sound like what I was talking about.

Const. boiling HCl boils at ~110°C, correct? That's only 10% off BP of H2O.

Sorry, you're right. My bad...