Question

If two liquids A and B form minimum boiling azeotrope at some specific composition then:

• A. A-B interactions are weaker than those between A-A or B-B.
• B. A-B interactions are stronger than those between A-A or B-B.
• C. The vapour pressure of the solution decreases because less number of molecules of liquids escape from the solution.
• D. The vapour pressure of the solution increases because more molecules of liquid A and B can escape from the solution.

Answer 1

Answer: (A), (D)

The vapour pressure of the solution increases because more molecules of liquid A and B can escape from the solution.

Explanation for the correct option:

Option (A):

• If two liquids A and B shows a large positive deviation from Rault’s law, they are said to form minimum boiling azeotrope at some specific composition.
• In this case of positive deviation from Rault’s law, A-B interactions are said to be weaker than those between the A-A and B-B interactions.

Option (D):

• In the case of solutions obtaining minimum boiling azeotrope, the vapor pressure of the solution increases because more molecules of liquid A and B can escape from the solution as A-B interactions get weaker than those between A-A and B-B interactions.

Explanation for the incorrect options:

Option (B):

• A-B interactions will be stronger than those between A-A or B-B, only when the two liquids will obtain maximum boiling azeotrope.
• Therefore, the option given here is not the correct concept.

Option (C):

• The vapor pressure of the solution increases in case of minimum boiling azeotrope because A-B interactions are said to be weaker than those between A-A and B-B interaction hence, more molecules of liquid A and B can escape from the solution.
• Hence the given Option does not coincide with the correct concept.

Hence, If two liquids A and B form minimum boiling azeotrope at some specific composition then: A-B interactions are weaker than those between A-A or B-B(Option A), and The vapor pressure of the solution increases because more molecules of liquid A and B can escape from the solution (Option D).