When `KMnO_(4)` solution is added to oxalic acid solution , the decolourisation is slow in the beginning but becomes instantaneous after some time because

Options

A. `CO_2` is formed as the product
B. reaction is exothermic
C. `MnO_4^(-)` catalyses the reaction
D. `Mn^(2+)` acts as autocatalyst.

Answer

To understand why the decolorization of KMnO4 solution in oxalic acid is slow at first but becomes instantaneous, we can break down the process step by step:

### Step 1: Identify the Reactants
- **KMnO4** (Potassium permanganate) is a strong oxidizing agent.
- **Oxalic acid** (C2O4^2-) is a reducing agent.

### Step 2: Understand the Reaction
- When KMnO4 is added to oxalic acid, a redox reaction occurs. The MnO4^- ion is reduced to Mn^2+, while the oxalic acid is oxidized to carbon dioxide (CO2).

The balanced chemical equation for the reaction can be represented as:
\[ 2 KMnO_4 + 5 C_2O_4^{2-} + 6 H^+ \rightarrow 2 Mn^{2+} + 10 CO_2 + 8 H_2O \]

### Step 3: Initial Reaction Rate
- Initially, the reaction is slow because there are no Mn^2+ ions present to facilitate the reaction. The concentration of the reactants is high, but without the presence of any catalyst, the reaction proceeds at a slower rate.

### Step 4: Formation of Mn^2+
- As the reaction progresses, Mn^2+ ions are formed. These ions have the ability to act as an autocatalyst, meaning they can speed up the reaction once they are present in sufficient quantities.

### Step 5: Increase in Reaction Rate
- Once enough Mn^2+ ions are produced, they enhance the reaction rate significantly, leading to a rapid decolorization of the KMnO4 solution. This is why the decolorization becomes instantaneous after some time.

### Conclusion
- The slow initial decolorization is due to the absence of Mn^2+ ions, which act as an autocatalyst. Once they are formed, they accelerate the reaction, resulting in a rapid decolorization of the solution.

### Final Answer
The decolorization of KMnO4 solution in oxalic acid is slow initially but becomes instantaneous due to the formation of Mn^2+ ions, which act as an autocatalyst.

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