Problem 16 - A Complete Resource Book in Chemistry for JEE Main

Question

How many electrons are involved in the oxidation by \(\mathrm{KMnO}_{4}\) in basic medium? (a) 5 (b) 3 (c) 2 (d) 1

Step-by-Step Solution

Answer

3 electrons are involved.

Step 1: Identify the Oxidation Reaction

In the basic medium, \(\mathrm{KMnO}_{4}\) acts as an oxidizing agent. The common reduction reaction involves the conversion of \(\mathrm{MnO}_{4}^{-}\) to \(\mathrm{MnO}_{2}\).

Step 2: Write the Reduction Half-Reaction

In basic medium, the reduction half-reaction of \(\mathrm{MnO}_{4}^{-}\) can be written as follows: \[\mathrm{MnO}_{4}^{-} + 2\ \mathrm{H}_2\mathrm{O} + 3\ \mathrm{e}^{-} \rightarrow \mathrm{MnO}_{2} + 4\ \mathrm{OH}^{-}\]

Step 3: Count the Electrons Involved

From the balanced reduction half-reaction, observe that 3 electrons (\( \mathrm{e}^{-} \)) are involved in reducing \(\mathrm{MnO}_{4}^{-}\) to \(\mathrm{MnO}_{2}\) in basic medium.

Key Concepts

KMnO4 in Basic Medium

Potassium permanganate (KMnO_4) is a strong oxidizing agent, often used in various chemical reactions.
When KMnO_4 is in a basic medium, it participates in oxidation-reduction reactions, where it acts as an agent that causes the oxidation of other substances while it itself gets reduced.
In a basic solution, KMnO_4 undergoes a specific transformation from the permanganate ion (MnO_4^{-}) to another manganese compound. This process is integral to the functioning of KMnO_4 as an oxidizing substance.
Here, MnO_4^{-} is effectively reduced to manganese dioxide (MnO_2). During this transformation, the solution retains its basic properties, facilitated by hydroxide ions (OH^{-}) that support the interaction. The reaction mechanism emphasizes the role of water, as MnO_4^{-} reacts with water molecules, interacting with electrons to ultimately form MnO_2. Understanding the behavior of KMnO_4 in a basic medium is essential for predicting the products of redox reactions and analyzing how KMnO_4 facilitates electron transfer.

Reduction Half-Reaction

A reduction half-reaction is a component of a redox process where a species gains electrons.
For KMnO_4 in basic medium, the reduction half-reaction provides valuable insight into how electrons are gained by the permanganate ion.
In the established reaction, MnO_4^{-} transitions to MnO_2. This shift involves the addition of three electrons, with the half-reaction impacted by water molecules and hydroxide ions.
Formally represented, the reduction half-reaction is:
yel MnO_4^{-} + 2 ext{H}_2 ext{O} + 3 ext{e}^{-} ightarrow ext{MnO}_2 + 4 ext{OH}^{-}. Additionally, balancing this equation ensures that both mass and charge are conserved, adhering to the principles of chemistry.
The balanced reduction half-reaction allows chemists to see exactly how electrons and other ions play a role in shifting between different states of manganese.

Electron Transfer

Electron transfer is a fundamental concept in chemistry, especially in oxidation-reduction reactions.
During the reduction process, KMnO_4 facilitates the transfer of electrons to the permanganate ion (MnO_4^{-}).
In the basic medium reaction, MnO_4^{-} accepts three electrons (e^{-}) to be transformed into manganese dioxide (MnO_2).
This process is essential as it accounts for the ability of substances like KMnO_4 to instigate changes in the oxidation states of other species.
This electron gaining behavior is key to the function of oxidizing agents like KMnO_4 in reactions.
Moreover, electron transfer is not just central to redox reactions but is also a principle in other fields such as biological electron transport chains and various industrial processes.