Which term describes mixtures that form when components have similar boiling points and cannot be separated by simple distillation due to violating Raoult's law?

• A. Solutions
• B. Azeotropes
• C. Suspensions
• D. Colloids

Answer: (B)

An azeotrope is a mixture that, at a specific composition, behaves like a single pure substance: it boils at a constant temperature and the vapor has the same composition as the liquid. This happens when the liquid deviates from Raoult's law in a way that makes the components’ volatilities effectively equal, so simple distillation can’t separate them further. In such cases, the relative volatility is about one, and you reach a fixed composition that cannot be enriched by ordinary distillation.

For example, ethanol and water form a minimum-boiling azeotrope around 95% ethanol, boiling at about 78.2 C at 1 atm; distillation cannot produce pure ethanol beyond that point without special techniques. Other terms like solutions, suspensions, and colloids describe different kinds of mixtures or dispersed systems and do not capture this non-ideal, constant-boiling behavior that defines an azeotrope.