Question

In order to oxidise a mixture of 1 mole each of FeC₂O₄, Fe₂(C₂O₄)₃, FeSO₄ and Fe₂(SO₄)₃ in acidic medium, the number of moles of KMnO₄ required is

• A. 3
• B. 2
• C. 5
• D. 7

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Potassium permanganate (\(\text{KMnO}_4\)) acts as a strong oxidizing agent in an acidic medium. To find the required moles, we calculate the total equivalents of the reducing agents in the mixture and equate them to the total equivalents of \(\text{KMnO}_4\).
Step 2: Key Formula or Approach:
Equivalents = Moles \(\times\) n-factor.
For \(\text{KMnO}_4\) in acidic medium: \(\text{Mn}^{+7} + 5e^- \to \text{Mn}^{+2}\) (n-factor = 5).
For reducing agents: n-factor is the total number of electrons lost per molecule during oxidation.
Equivalents of \(\text{KMnO}_4\) = Total Equivalents of mixture.
Step 3: Detailed Explanation:
Calculate the n-factor for each 1-mole component of the mixture:
1. \(\text{FeC}_2\text{O}_4\) (Ferrous oxalate):
\(\text{Fe}^{+2} \to \text{Fe}^{+3} + 1e^-\)
\(\text{C}_2\text{O}_4^{-2} \to 2\text{CO}_2 + 2e^-\)
Total electrons lost = \(1 + 2 = 3\). Thus, n-factor = 3.
2. \(\text{Fe}_2(\text{C}_2\text{O}_4)_3\) (Ferric oxalate):
\(\text{Fe}\) is already in the \(+3\) state, so it cannot be oxidized further.
\(3 \times (\text{C}_2\text{O}_4^{-2} \to 2\text{CO}_2 + 2e^-)\)
Total electrons lost = \(3 \times 2 = 6\). Thus, n-factor = 6.
3. \(\text{FeSO}_4\) (Ferrous sulfate):
\(\text{Fe}^{+2} \to \text{Fe}^{+3} + 1e^-\)
The sulfate ion (\(\text{SO}_4^{-2}\)) cannot be further oxidized.
Total electrons lost = 1. Thus, n-factor = 1.
4. \(\text{Fe}_2(\text{SO}_4)_3\) (Ferric sulfate):
Both \(\text{Fe}^{+3}\) and \(\text{SO}_4^{-2}\) are in their maximum oxidation states and cannot be oxidized.
Total electrons lost = 0. Thus, n-factor = 0.
Total equivalents of the reducing mixture = \((1 \times 3) + (1 \times 6) + (1 \times 1) + (1 \times 0) = 3 + 6 + 1 + 0 = 10\) equivalents.
Now, equate with \(\text{KMnO}_4\):
Moles of \(\text{KMnO}_4 \times (\text{n-factor of } \text{KMnO}_4)\) = Total equivalents
\(x \times 5 = 10 \implies x = \frac{10}{5} = 2 \text{ moles}\).
Step 4: Final Answer:
2 moles of \(\text{KMnO}_4\) are required.