The cleansing action of soap is due to the

Options

A. the presence of `Na^+` ions in water
B. its dissociation into ions in water
C. the formation of associated colloids
D. its action as emulsifying agent

Answer

To solve the question about the cleansing action of soap, we can break down the explanation into clear steps:

### Step-by-Step Solution:

1. **Understanding Soap Structure**:
- Soap molecules consist of two distinct parts: a hydrophilic (water-attracting) polar head and a hydrophobic (water-repelling) non-polar tail.
- The polar head typically contains a carboxylate group, making it soluble in water, while the hydrocarbon tail is non-polar and soluble in oils and greases.

**Hint**: Remember that the structure of soap is crucial to its function; it has both a water-loving and a water-repelling part.

2. **Formation of Micelles**:
- When soap is added to water, the molecules arrange themselves into structures called micelles. In these micelles, the hydrophobic tails face inward, away from the water, while the hydrophilic heads face outward, interacting with the water.

**Hint**: Visualize micelles as tiny spheres with the tails hidden inside and the heads on the outside.

3. **Interaction with Dirt and Grease**:
- The hydrophobic tails of the soap molecules interact with grease and dirt, which are also non-polar. This interaction allows the soap to surround the grease particles.
- The polar heads remain in contact with the water, allowing the grease to be lifted away from surfaces (like cloth) and suspended in water.

**Hint**: Think of soap as a bridge between water and grease, allowing them to mix.

4. **Reduction of Surface Tension**:
- Soap reduces the surface tension of water, which helps the water to spread and wet the surface of the cloth more effectively.
- This increased wetting allows the soap to penetrate and lift dirt and grease more efficiently.

**Hint**: Surface tension is what makes water bead up; soap helps break that tension.

5. **Emulsification**:
- The soap action leads to the formation of an emulsion, where grease is broken into small droplets that remain suspended in water due to repulsion between the droplets.
- This prevents the grease from re-depositing on the cloth, allowing it to be rinsed away.

**Hint**: Emulsification is key to keeping dirt and grease suspended in water so they can be washed away.

6. **Conclusion**:
- The cleansing action of soap is primarily due to its ability to act as an emulsifying agent, allowing dirt and grease to be removed from surfaces and suspended in water.

**Hint**: Emulsifying agents are substances that help mix two immiscible liquids, like oil and water.

### Final Answer:
The cleansing action of soap is due to its action as an emulsifying agent.