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

The reduction of the permanganate ion (MnO4-) is a fascinating topic in redox chemistry, particularly because it showcases how the medium can influence the number of electrons involved in the reaction. To answer your question directly, the correct option is (D) 5 electrons in acidic medium. Let’s break this down to understand why this is the case.

The Chemistry of Permanganate Ion

The permanganate ion is a strong oxidizing agent, and its reduction can occur in different media—acidic, neutral, or alkaline. The final product of this reduction is manganese(II) ion (Mn2+), which is colorless in solution.

Reduction in Acidic Medium

In an acidic environment, the reduction of permanganate occurs as follows:

• The half-reaction can be represented as: MnO4- + 8H+ + 5e- → Mn2+ + 4H2O
• This shows that 5 electrons are transferred during the reduction process.

The presence of hydrogen ions (H+) from the acid is crucial here, as they help balance the charge and facilitate the reduction of manganese from its +7 oxidation state in permanganate to +2 in manganese(II) ion.

Reduction in Other Media

Now, let’s consider the other options:

• Neutral Medium: In a neutral medium, the reduction of permanganate typically involves 3 electrons, leading to the formation of manganese dioxide (MnO2) instead of Mn2+.
• Alkaline Medium: In alkaline conditions, the reduction also involves 3 electrons, producing manganese dioxide (MnO2) as well.

Thus, the number of electrons involved in the reduction process varies significantly depending on the pH of the solution.

Summary of Key Points

To summarize:

• In acidic medium, permanganate is reduced by 5 electrons to form Mn2+.
• In neutral or alkaline medium, it is reduced by 3 electrons, typically forming MnO2.

This behavior illustrates the importance of the reaction environment in redox chemistry. Understanding these differences is crucial for predicting the outcomes of reactions involving permanganate in various conditions.