Question

What is the colour change occurring while the conversion of Fe²⁺⟶ to Fe³⁺ using KMnO₄?

• A. Blue ⟶ yellow
• B. Green ⟶ violet
• C. Green ⟶ yellow
• D. Yellow ⟶ green

Answer 1

The Correct Option is C

The oxidation of Fe²⁺ to Fe³⁺ using potassium permanganate (KMnO₄) involves distinct color changes that serve as visual indicators of the reaction:

1. Initial Colors:
- Fe²⁺ solution: Pale green (hexaaquairon(II) complex, [Fe(H₂O)₆]²⁺)
- KMnO₄ solution: Intense purple (MnO₄^- ions)

2. During the Reaction:
As KMnO₄ is added:
- The purple color of MnO₄^- disappears as it's reduced to colorless Mn²⁺
- The solution turns yellow-brown due to formation of Fe³⁺ (hexaaquairon(III) complex, [Fe(H₂O)₆]³⁺)

3. Final Observation:
At the endpoint:
- One persistent pale pink color appears (from excess MnO₄^-)
- The overall solution color changes from pale green → yellow-brown → pale pink

4. Chemical Equation:
The redox reaction can be represented as:
\[ 5\text{Fe}^{2+} + \text{MnO}_4^- + 8\text{H}^+ \rightarrow 5\text{Fe}^{3+} + \text{Mn}^{2+} + 4\text{H}_2\text{O} \]

5. Practical Significance:
This color change sequence makes KMnO₄ an excellent:
- Oxidizing agent for Fe²⁺
- Self-indicator in titrations
- The endpoint is marked by the first permanent pale pink color

Final Answer:
The color change sequence is:
\(\boxed{\text{Pale green} \rightarrow \text{Yellow-brown} }\)