Azeotropes and Raoult’s law: a binary azeotrope that boils at a temperature higher than either pure component shows which kind of deviation from Raoult’s law?

Introduction / Context:
Understanding deviations from Raoult’s law is essential to predict vapor–liquid equilibria, design distillation columns, and anticipate azeotrope formation. Maximum-boiling and minimum-boiling azeotropes exhibit characteristic deviations that influence separation feasibility.

Given Data / Assumptions:

• Binary liquid mixture at atmospheric pressure.
• Azeotrope has a boiling point higher than that of both pure components (maximum-boiling azeotrope).

Concept / Approach:
Raoult’s law assumes ideal solutions where each component’s partial pressure equals its mole fraction times its pure-component vapor pressure. Real mixtures may deviate because of intermolecular interactions. Stronger unlike-molecule attractions reduce escaping tendency, lowering total vapor pressure at a given temperature. This produces a higher boiling point than either component and constitutes negative deviation from Raoult’s law.

Step-by-Step Solution:

Verification / Alternative check:
Systems like hydrochloric acid–water at certain compositions display maximum-boiling behavior consistent with negative deviations (enhanced attractions).

Why Other Options Are Wrong:

• Positive deviation: corresponds to weaker unlike interactions, lower boiling, and minimum-boiling azeotropes.
• No deviation: would be ideal behavior, no azeotrope.
• None of these: not applicable because negative deviation is correct.

Common Pitfalls:
Confusing sign of deviation with direction of boiling point; assuming all azeotropes are minimum-boiling; ignoring pressure dependence of azeotrope behavior.

Final Answer:
Negative deviation