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

Question

A binary solution of liquids A and B deviates positively from Raoult's law. Which of the following statements is NOT true for this solution?

A.RAMA NAGESWARARAO · Accepted Answer

## CORE INFORMATION
✓ **Answer**: [B]
## CONCEPT FRAMEWORK
	**Primary Concept**: Raoult's Law and Deviations
	**Related Topics**: Ideal Solutions, Non-ideal Solutions, Intermolecular Forces, Vapor Pressure, Enthalpy of Mixing, Volume of Mixing
	**Prerequisites**: Understanding of ideal and non-ideal solutions, Raoult's law, intermolecular forces, thermodynamics of mixing.
## SOLUTION PATHWAY
**Given Information**:
	* The solution of liquids A and B shows positive deviation from Raoult's law.
**Method & Steps**:
	1. **Understanding Positive Deviation**: A positive deviation from Raoult's law occurs when the vapor pressure of the solution is higher than predicted by Raoult's law. This implies weaker intermolecular forces between A and B molecules compared to the forces within pure A and pure B.
	2. **Analyzing Option A**: If there's a positive deviation, the actual vapor pressure of the solution is higher than the ideal vapor pressure. Thus, option A is true.
	3. **Analyzing Option B**: Positive deviation arises because the intermolecular forces between A-B are weaker than A-A and B-B. Hence, option B is NOT true.
	4. **Analyzing Option C**: Weaker A-B interactions mean that energy is required to break the A-A and B-B interactions, leading to an endothermic mixing process. Therefore, the enthalpy of mixing ($\Delta H_{mix}$) is positive. Option C is true.
	5. **Analyzing Option D**: Weaker interactions also often result in a larger final volume compared to the sum of individual volumes. The volume of mixing ($\Delta V_{mix}$) is positive. Option D is true.
**Result**: The statement that is NOT true is option B.
**Verification**: By understanding the definition of positive deviation, we can confirm that options A, C, and D are consistent with it, while option B contradicts it.
 ## OPTION ANALYSIS
[A] :x: The total vapor pressure is indeed higher than the ideal vapor pressure for positive deviations. Thus, this statement is true.
[B] ✓: This statement is false because positive deviation implies weaker A-B interactions compared to A-A and B-B interactions.
[C] :x:  The enthalpy of mixing is positive because energy is required to overcome stronger A-A and B-B interactions. Thus, this statement is true.
[D] :x: The volume of mixing is positive because weaker A-B interactions lead to a larger final volume. Thus, this statement is true.
 ## LEARNING AIDS
	**Common Mistakes**:
		1. **Confusing Positive and Negative Deviations**: Remember that positive deviations mean weaker A-B interactions and higher vapor pressure, while negative deviations mean stronger A-B interactions and lower vapor pressure.
		2. **Incorrectly Relating Intermolecular Forces**: A positive deviation does not mean stronger A-B forces. It means the opposite. The opposite is true for negative deviations.
	**Quick Tips**:
		1. **Visualize:** Imagine the molecules having weaker attraction to each other, leading to more molecules escaping into the vapor phase.
		2. **Mnemonic**: Remember 'Positive' starts with 'P' which can be associated with 'Pressure' being higher than ideal.

A.RAMA NAGESWARARAO · Answer

The total vapour pressure of the solution is greater than the ideal vapour pressure.

A.RAMA NAGESWARARAO · Answer

The correct Option is "The intermolecular forces between A-A and B-B are stronger than those between A-B."

A.RAMA NAGESWARARAO · Answer

The enthalpy of mixing ($\Delta H_{mix}$) is positive.

A.RAMA NAGESWARARAO · Answer

The volume of mixing ($\Delta V_{mix}$) is positive.

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