To solve the question regarding the titration of oxalic acid with KMnO4, we need to understand the behavior of the reaction at different stages of the titration and the role of manganese ions (Mn²⁺) as a catalyst.
### Step-by-Step Solution:
1. **Understanding the Reaction**:
- When oxalic acid (C₂H₂O₄) is titrated with potassium permanganate (KMnO₄) in an acidic medium, the reaction involves the oxidation of oxalic acid to carbon dioxide (CO₂) and the reduction of permanganate ions (MnO₄⁻) to manganese ions (Mn²⁺).
2. **Initial Slow Decolorization**:
- In the beginning, when KMnO₄ is added, the decolorization is slow. This is because the concentration of Mn²⁺ ions, which act as a catalyst, is low at the start of the reaction. The reaction proceeds at a slower rate as there are fewer Mn²⁺ ions available to facilitate the reaction.
3. **Formation of Mn²⁺**:
- As the titration continues and more KMnO₄ is added, Mn²⁺ ions are produced as a product of the reaction. These ions are formed as the KMnO₄ is reduced.
4. **Autocatalysis**:
- The key point is that Mn²⁺ ions produced in the reaction act as an autocatalyst. This means that as the concentration of Mn²⁺ increases, it accelerates the reaction rate. Therefore, after the initial slow phase, the reaction begins to speed up significantly.
5. **Rapid Decolorization**:
- Eventually, the presence of a higher concentration of Mn²⁺ ions leads to a rapid decolorization of the solution. This is due to the autocatalytic effect, where the product of the reaction (Mn²⁺) enhances the rate of the reaction itself.
6. **Conclusion**:
- Therefore, the reason for the slow initial decolorization followed by rapid decolorization is that Mn²⁺, produced during the reaction, acts as an autocatalyst, increasing the reaction rate as its concentration rises.
### Final Answer:
The first few drops of KMnO₄ are decolorized slowly due to the low concentration of Mn²⁺ ions, but as the reaction progresses, Mn²⁺ ions are produced and act as an autocatalyst, leading to rapid decolorization later.
