Question

Which of the following oxidation reactions are carried out by both \( K_2Cr_2O_7 \) and \( KMnO_4 \) in acidic medium?
A. \( I^- \rightarrow I_2 \)
B. \( S^{2-} \rightarrow S \)
C. \( Fe^{2+} \rightarrow Fe^{3+} \)
D. \( I^- \rightarrow IO_3^- \)
E. \( S_2O_3^{2-} \rightarrow SO_4^{2-} \)
Choose the correct answer from the options given below:

• A. A, B and C Only
• B. A, D and E Only
• C. B, C and D Only
• D. C, D and E Only

Hint:

When dealing with strong oxidizers, always check which ions they can oxidize in acidic conditions.

Answer 1

The Correct Option is A

Let's analyze each oxidation reaction:

A. $I^- \rightarrow I_2$:
Both $K_2Cr_2O_7$ and $KMnO_4$ can oxidize iodide to iodine in acidic medium.
This reaction is possible with both oxidizing agents.

B. $S^{2-} \rightarrow S$:
Both $K_2Cr_2O_7$ and $KMnO_4$ can oxidize sulfide to sulfur in acidic medium.
This reaction is possible with both oxidizing agents.

C. $Fe^{2+} \rightarrow Fe^{3+}$:
Both $K_2Cr_2O_7$ and $KMnO_4$ can oxidize $Fe^{2+}$ to $Fe^{3+}$ in acidic medium.
This reaction is possible with both oxidizing agents.

D. $I^- \rightarrow IO_3^-$:
Both $K_2Cr_2O_7$ and $KMnO_4$ can oxidize iodide to iodate in acidic medium, but it requires a stronger oxidizing power.
This reaction is possible under strong conditions, but not always consistent in standard acidic conditions.

E. $S_2O_3^{2-} \rightarrow SO_4^{2-}$:
Thiosulfate oxidation to sulfate is more complex and specific to certain oxidizing power and conditions. $KMnO_4$ typically does not oxidize thiosulfate to sulfate quantitatively in acidic medium, while $K_2Cr_2O_7$ may do so under vigorous conditions.
This reaction is not consistently carried out by both oxidizing agents.

Therefore, reactions A, B, and C are the only ones that are consistently carried out by both $K_2Cr_2O_7$ and $KMnO_4$ under standard acidic conditions.

Final Answer:
The final answer is $ (3)\ A,\ B\ \text{and}\ C\ \text{only} $.

Answer 2

Step 1: Understand the problem.
We are asked which oxidation reactions can be carried out by both \( K_2Cr_2O_7 \) (potassium dichromate) and \( KMnO_4 \) (potassium permanganate) in acidic medium.
Both are strong oxidizing agents that can oxidize several ions, but the extent of oxidation depends on the reaction medium (acidic, basic, or neutral).

Step 2: Recall oxidation capabilities in acidic medium.
In acidic medium:
- \( K_2Cr_2O_7 \) acts as a powerful oxidizing agent, reduced to \( Cr^{3+} \).
- \( KMnO_4 \) acts as a stronger oxidizing agent, reduced to \( Mn^{2+} \).

Both can oxidize similar species such as iodide, sulfide, and ferrous ions.

Step 3: Analyze each option.
(A) \( I^- \rightarrow I_2 \):
Both \( K_2Cr_2O_7 \) and \( KMnO_4 \) oxidize iodide ions to iodine. ✅

(B) \( S^{2-} \rightarrow S \):
Both reagents oxidize sulfide ions to elemental sulfur. ✅

(C) \( Fe^{2+} \rightarrow Fe^{3+} \):
Both oxidize ferrous ions to ferric ions. ✅

(D) \( I^- \rightarrow IO_3^- \):
This is a more extensive oxidation; \( KMnO_4 \) can achieve this, but \( K_2Cr_2O_7 \) cannot carry out this oxidation completely in acidic medium. ❌

(E) \( S_2O_3^{2-} \rightarrow SO_4^{2-} \):
This reaction occurs only with strong oxidizers like \( KMnO_4 \), not with \( K_2Cr_2O_7 \) under similar conditions. ❌

Step 4: Conclusion.
Reactions (A), (B), and (C) are common to both \( K_2Cr_2O_7 \) and \( KMnO_4 \) in acidic medium.

Final Answer:
\[ \boxed{A, B, \text{ and } C \text{ only}} \]