Which of the following reactions are disproportionation reactions?
(A) Cu⁺ → Cu²⁺ + Cu
(B) 2 KMnO₄ → K₂MnO₄ + MnO₂ + 2 H₂O
(C) 2 KMnO₄ → K₂MnO₄ + MnO₂ + O₂
(D) 2 MnO₄⁻ + 3 Mn²⁺ + 2 H₂O → 5 MnO₂ + 4 H⁺
Choose the correct answer from the options given below:
(A), (B)
Answer (2)
Only reaction (A) is a disproportionation reaction, where Cu⁺ is simultaneously oxidized to Cu²⁺ and reduced to Cu. Reactions (B), (C), and (D) do not involve the same element being both oxidized and reduced. Therefore, the answer is (A).
;
A disproportionation reaction is a specific type of redox reaction where a single substance is simultaneously oxidized and reduced, forming two different products. To determine which reactions are disproportionation reactions, we need to analyze each given reaction:
(A) Cu + → Cu 2 + + Cu
In this reaction, the same element, copper ( Cu ) , is both oxidized and reduced. Copper is oxidized from Cu + to Cu 2 + and simultaneously reduced from Cu + to Cu . Since the copper ion undergoes both oxidation and reduction, this reaction is a disproportionation reaction.
(B) 2 KMnO 4 → K 2 MnO 4 + MnO 2 + 2 H 2 O
Here, the manganese in KMnO 4 changes to two different oxidation states in the products: K 2 MnO 4 (where Mn has an oxidation state of +6) and MnO 2 (where Mn has an oxidation state of +4). The manganese is reduced from +7 in KMnO 4 to +4 in MnO 2 and oxidized from +7 in KMnO 4 to +6 in K 2 MnO 4 . Thus, it is also a disproportionation reaction.
(C) 2 KMnO 4 → K 2 MnO 4 + MnO 2 + O 2
Similar to reaction (B), manganese changes from +7 in KMnO 4 to +6 in K 2 MnO 4 and +4 in MnO 2 . While this involves changes in manganese's oxidation states, the formation of O 2 adds a complexity where determining it as pure disproportionation is less clear from the given options.
(D) 2 MnO 4 − + 3 Mn 2 + + 2 H 2 O → 5 MnO 2 + 4 H +
In this reaction, there is no single substance undergoing both oxidation and reduction but rather multiple manganese species interacting. This is not indicative of a classic disproportionation reaction based on the shared element being oxidized and reduced simultaneously in a single reactant.
Based on the analysis, reactions (A) and (B) are disproportionation reactions. Thus, the correct choice is (A), (B) .
