When a blue litmus is dipped into a solution of hypochlorous acid, It turns red and then gets decolourised. Explain.

Answer

To explain why a blue litmus turns red and then gets decolorized when dipped into a solution of hypochlorous acid (HOCl), we can break down the process into clear steps:

### Step-by-Step Solution:

1. **Understanding Hypochlorous Acid (HOCl)**:
- Hypochlorous acid is a weak acid that can dissociate in solution to release hydrogen ions (H⁺) and hypochlorite ions (OCl⁻).

2. **Effect on Blue Litmus**:
- Blue litmus paper is used to test for acidity. When it comes into contact with an acidic solution, it changes color.
- In the case of HOCl, the dissociation produces H⁺ ions, which makes the solution acidic.
- The presence of H⁺ ions causes the blue litmus to turn red, indicating the acidic nature of the solution.

3. **Bleaching Action of Hypochlorous Acid**:
- Hypochlorous acid also has bleaching properties due to the presence of nascent oxygen (O) that can be generated during its reactions.
- When HOCl is present, it can decompose to release nascent oxygen, which is a powerful oxidizing agent.

4. **Decolorization of Red Litmus**:
- The nascent oxygen can react with the dye in the litmus paper, leading to its decolorization.
- This means that after initially turning red due to the acidic nature of the solution, the red litmus loses its color because of the bleaching action of the nascent oxygen.

### Summary:
In summary, when blue litmus is dipped into hypochlorous acid, it first turns red due to the release of H⁺ ions, indicating acidity. Subsequently, the nascent oxygen produced from the hypochlorous acid bleaches the dye in the litmus paper, resulting in decolorization.