The Question is from neet-chemistry solutions , and it was created by the author A.RAMA NAGESWARARAO

Question

A binary solution of two volatile liquids A and B deviates negatively from Raoult's Law.  At a specific composition, the total vapor pressure is minimum. Which of the following statements is FALSE regarding this specific composition?

A.RAMA NAGESWARARAO · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
	**Primary Concept**: Raoult's Law and Deviations
	**Related Topics**: Azeotropes, Vapor Pressure, Intermolecular Forces
	**Prerequisites**: Understanding of Raoult's Law, ideal and non-ideal solutions.
## SOLUTION PATHWAY
**Given Information**:
	Binary solution of A and B.
	Negative deviation from Raoult's Law.
	Total vapor pressure is minimum at a specific composition.
**Method & Steps**:
	1. **Negative Deviation**: Negative deviation occurs when the intermolecular forces between A and B are stronger than those within pure A or pure B. This leads to a lower than expected vapor pressure.
		Reasoning: Stronger A-B interactions stabilize the liquid phase, making it harder for molecules to escape into the vapor phase.
	2. **Minimum Vapor Pressure**:  The specific composition at which the total vapor pressure is minimum is called an azeotrope.  At this point, the solution behaves like a pure substance with a constant boiling point.
		Key Point: At the azeotropic composition, the liquid and vapor phases have identical compositions.
	3. **Vapor Composition**: The mole fraction of a component in the vapor phase is related to its partial pressure and the total pressure.  It's not necessarily true that one component will always have a higher mole fraction in the vapor than the other, especially in a negative azeotrope.
		Result: The statement 'The mole fraction of A in the vapor is always greater than that of B' is false.
		Verification:  The relative mole fractions in the vapor depend on the specific properties of A and B and their interactions, and it's possible for B to have a higher mole fraction in the vapor at some compositions, even with a negative deviation.
## OPTION ANALYSIS
[A] ✓: At the azeotropic composition (minimum vapor pressure), the vapor and liquid have the same composition.
[B] ✓: Due to stronger A-B interactions, more energy is required to overcome these interactions and vaporize the liquid. Thus, the boiling point is elevated at the azeotropic composition compared to pure A or B.
[C] ✓: The question explicitly states the system deviates negatively from Raoult's Law.
[D] :x:  The mole fraction of A in the vapor is NOT always greater than that of B.  It depends on the specific nature of the A-B interactions and their relative volatilities.  At the azeotropic point, the mole fractions are the same in both liquid and vapor phases.  It's possible for B to have a higher mole fraction in the vapor at other compositions even with a negative deviation.
## LEARNING AIDS
	**Common Mistakes**:
		1. Assuming the component with the lower boiling point will always have a higher mole fraction in the vapor: This is not true for non-ideal solutions, particularly azeotropes.
		2. Confusing positive and negative deviations: Remember negative deviation implies stronger A-B interactions and lower vapor pressure.
	**Quick Tips**:
		1. For negative deviations, think 'lower vapor pressure, higher boiling point'.
		2. Azeotropes have the same composition in liquid and vapor phases at the specific azeotropic composition.

A.RAMA NAGESWARARAO · Answer

The vapor and liquid phases have identical compositions.

A.RAMA NAGESWARARAO · Answer

The boiling point is higher than that of either pure A or pure B.

A.RAMA NAGESWARARAO · Answer

The system deviates negatively from Raoult's Law.

A.RAMA NAGESWARARAO · Answer

The correct Option is "The mole fraction of A in the vapor is always greater than that of B."

NEET Chemistry Solutions MCQs

Select Topic

Question Tags

Question Tags

Question Tags

Question Tags

Question Tags

Question Tags

Question Tags

Question Tags

Question Tags

Question Tags

NEET Subjects

Our Bots

Company