An azeotrope is defined as a mixture that boils to vapor with what property?

An azeotrope is defined as a mixture that boils to vapor with what property?

• A. The vapor has the same composition as the liquid.
• B. The vapor is completely different in composition.
• C. The vapor has higher pressure than the liquid.
• D. The vapor cannot be condensed.

Answer: (A)

The key idea is that at an azeotropic point the liquid and its vapor have identical compositions. When a mixture boils at this point, the vapor that forms has the same makeup as the liquid, so the overall composition doesn’t change during boiling. This is why simple distillation can’t separate the components beyond that point—the relative volatility is effectively one. Azeotropes arise from non-ideal interactions between components, which cause the vapor and liquid phases to align in composition at a specific boiling point. The fact that the vapor, like the liquid, shares the same composition is the defining feature, not differences in pressure or the ability to condense.

The key idea is that at an azeotropic point the liquid and its vapor have identical compositions. When a mixture boils at this point, the vapor that forms has the same makeup as the liquid, so the overall composition doesn’t change during boiling. This is why simple distillation can’t separate the components beyond that point—the relative volatility is effectively one.

Azeotropes arise from non-ideal interactions between components, which cause the vapor and liquid phases to align in composition at a specific boiling point. The fact that the vapor, like the liquid, shares the same composition is the defining feature, not differences in pressure or the ability to condense.