Question:

In dilute alkaline solution, $ \text{MnO}_4^- $ changes to

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In alkaline solutions, potassium permanganate ($ \text{MnO}_4^- $) is reduced to manganate ions ($ \text{MnO}_4^{2-} $), which results in a color change from purple to green.

Updated On: May 3, 2025

$ \text{MnO}_2 $
$ \text{MnO}_4^{2-} $
$ \text{MnO} $
$ \text{Mn}_2\text{O}_3 $

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The Correct Option is B

Approach Solution - 1

In a dilute alkaline solution, the permanganate ion $ \text{MnO}_4^- $ undergoes a chemical reduction reaction to form the manganate ion $ \text{MnO}_4^{2-} $. This process can be explained by analyzing the changes in oxidation states and balancing the resultant half-reaction in a basic environment.

When potassium permanganate $ \text{KMnO}_4 $ is dissolved in a dilute alkaline solution, the $\text{MnO}_4^-$ ion is reduced. The reaction can be represented as follows:

Reduction half-reaction:

$ \text{MnO}_4^- + e^- \rightarrow \text{MnO}_4^{2-} $

In this reaction, the oxidation state of manganese changes from +7 in $ \text{MnO}_4^- $ to +6 in $ \text{MnO}_4^{2-} $. This change indicates a gain of one electron, demonstrating a reduction process. In an alkaline medium, the addition of hydroxide ions $ \text{OH}^- $ assists in maintaining charge balance:

$ \text{MnO}_4^- + \text{e}^- + \text{OH}^- \rightarrow \text{MnO}_4^{2-} + \text{OH}^- $

Thus, in dilute alkaline conditions, $ \text{MnO}_4^- $ will most commonly convert into $ \text{MnO}_4^{2-} $, which is known as the manganate ion.

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Approach Solution -2

In a dilute alkaline solution, permanganate ion ($\text{MnO}_4^-$) undergoes a reduction reaction. The permanganate ion is a strong oxidizing agent, and in such a basic environment, it will be reduced to manganate ion ($\text{MnO}_4^{2-}$). This can be represented by the following half-reaction:

\[\text{MnO}_4^- + e^- \rightarrow \text{MnO}_4^{2-}\]

This reduction occurs because the alkaline environment provides the necessary conditions for the transformation of the $\text{MnO}_4^-$ ion into the $\text{MnO}_4^{2-}$ ion. Both ions have different oxidation states of manganese, $\text{Mn}$ in $\text{MnO}_4^-$ is in the +7 oxidation state, while in $\text{MnO}_4^{2-}$, it is in the +6 oxidation state, indicating a reduction process by the gain of an electron.