IIT-JEE 2011 · Paper 2 · Chemistry Q9 · Dronacharya Exams

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ChemistryMultiple correct+4Question 9 of 60

Reduction of the metal centre in aqueous permanganate ion involves

A

3 electrons in neutral medium

B

5 electrons in neutral medium

C

3 electrons in alkaline medium

D

5 electrons in acidic medium

Answer and worked solution

Official answer: A, C, D

Half-reactions.

Acidic: $\ce{MnO4- + 8H+ + 5e- -> Mn^{2+} + 4H2O}$ (5 electrons).
Neutral or weakly alkaline: $\ce{MnO4- + 2H2O + 3e- -> MnO2 + 4OH-}$ (3 electrons).
Strongly alkaline: $\ce{MnO4- + e- -> MnO4^{2-}}$ (1 electron), but the usual alkaline oxidations go to $\ce{MnO2}$ (3 electrons).

(A), (C), (D)

Topics:Important compounds (KMnO4, K2Cr2O7)Balancing redox reactions

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