The Question is from neet-chemistry surface-chemistry emulisions-soaps-and-detergents, and it was created by the author Mr. S M HUSSAIN

Question

A mixture of two immiscible liquids A and B forms an emulsion. The interfacial tension between A and B is $\gamma$. A surfactant is added to stabilize the emulsion. Which of the following statements is TRUE regarding the effect of the surfactant on $\gamma$ and the stability of the emulsion?

Mr. S M HUSSAIN · Accepted Answer

## CORE INFORMATION
✓ **Answer**: A
## CONCEPT FRAMEWORK
 **Primary Concept**: Interfacial tension and emulsion stability
 **Related Topics**: Surfactants, surface chemistry
 **Prerequisites**: Understanding of interfacial tension, emulsion formation, and the role of surfactants.
## SOLUTION PATHWAY
**Given Information**:
  Two immiscible liquids A and B form an emulsion.
  Interfacial tension between A and B is $\gamma$.
  A surfactant is added.
**Method & Steps**:
 1. Understand the role of interfacial tension in emulsion stability.
  Reasoning:  A high interfacial tension between two immiscible liquids leads to a tendency for the liquids to separate.  A lower interfacial tension promotes greater stability because the interfacial area is minimized.
  Formula/Rule: No specific formula is needed for this conceptual question.
 2. Consider the effect of a surfactant on interfacial tension.
  Working: Surfactants are amphiphilic molecules (having both hydrophilic and hydrophobic parts). They adsorb at the interface between the two liquids, reducing the interfacial tension ($\gamma$).
  Key Point:  The surfactant molecules orient themselves with their hydrophobic tails towards the nonpolar liquid and their hydrophilic heads towards the polar liquid (or vice-versa, depending on the polarity of the liquids and surfactant). This reduces the attractive forces between the two liquid phases.
 3. Relate the change in interfacial tension to emulsion stability.
  Result: By reducing $\gamma$, the surfactant increases the stability of the emulsion because the smaller interfacial tension reduces the tendency of the two liquids to separate.
  Verification: This is consistent with the known function of surfactants in stabilizing emulsions.
 ## OPTION ANALYSIS
A] ✓: The surfactant decreases $\gamma$, increasing the emulsion's stability. (Correct. This is the explanation above.)
B] :x: The surfactant increases $\gamma$, increasing the emulsion's stability. (Incorrect. Increasing interfacial tension would decrease stability.)
C] :x: The surfactant decreases $\gamma$, decreasing the emulsion's stability. (Incorrect. Decreasing interfacial tension increases stability.)
D] :x: The surfactant increases $\gamma$, decreasing the emulsion's stability. (Incorrect. This is consistent with the behaviour of a system without surfactant, but not with the added surfactant.)
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the effect of surfactants on interfacial tension: Remembering that surfactants *reduce* interfacial tension is crucial.
  2.Misunderstanding the relationship between interfacial tension and emulsion stability: Lower interfacial tension means higher stability.
 **Quick Tips**:
  1.Think of surfactants as reducing the 'surface energy' between the two liquids.
  2.Remember the amphiphilic nature of surfactants and how this allows them to reduce the interfacial tension.

Mr. S M HUSSAIN · Answer

The correct Option is "The surfactant decreases $\gamma$, increasing the emulsion's stability."

Mr. S M HUSSAIN · Answer

The surfactant increases $\gamma$, increasing the emulsion's stability.

Mr. S M HUSSAIN · Answer

The surfactant decreases $\gamma$, decreasing the emulsion's stability.

Mr. S M HUSSAIN · Answer

The surfactant increases $\gamma$, decreasing the emulsion's stability.

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