\(KMnO_4\) is a strong oxidizing agent in acidic medium. To provide acidic medium \(H_2SO_4\) si used instead of \(HCl\). This is because

\(HCl\) is oxidized by \(KMnO_4\) to \(Cl_2\)

The correct answer is option 2. \(HCl\) is oxidized by \(KMnO_4\) to \(Cl_2\).

Let us delve deeper into why sulfuric acid (\(H_2SO_4\)) is preferred over hydrochloric acid (\(HCl\)) when using potassium permanganate (\(KMnO_4\)) as an oxidizing agent in acidic conditions.

Potassium Permanganate (\(KMnO_4\)) as an Oxidizing Agent

Strong Oxidizer: \(KMnO_4\) is known for its strong oxidizing properties. In an acidic medium, it gets reduced while oxidizing other substances. For example, it can oxidize hydrogen sulfide (\(H_2S\)) to sulfate (\(SO_4^{2-}\)).

Acidic Medium Requirement

Acidic Conditions: \(KMnO_4\) requires an acidic medium to effectively act as an oxidizing agent. This is because the oxidation state of manganese in \(KMnO_4\) changes from +7 to +2 (or other states) depending on the reduction conditions. The acidic medium helps in achieving this reduction.

Comparison Between \(HCl\) and \(H_2SO_4\)

Hydrochloric Acid (\(HCl\))

Reaction with \(KMnO_4\): In the presence of \(KMnO_4\), hydrochloric acid can be oxidized to chlorine gas (\(Cl_2\)). This reaction is as follows:

\(2KMnO_4 + 16HCl \rightarrow 2MnCl_2 + 5Cl_2 + 8H_2O\)

Impact on Reaction: The production of chlorine gas (\(Cl_2\)) can interfere with the oxidation process that you intend to carry out. \(Cl_2\) is a strong oxidizing agent itself and can react with other substances in your mixture, complicating the reaction and consuming \(KMnO_4\).

Sulfuric Acid (\(H_2SO_4\))

Non-reaction with \(KMnO_4\): Sulfuric acid, unlike hydrochloric acid, does not get oxidized by \(KMnO_4\) under the same conditions. It remains stable and does not produce chlorine gas or interfere with the oxidation process.

Suitable for Reaction: Since \(H_2SO_4\) does not react with \(KMnO_4\) in a way that consumes the oxidizer or produces unwanted by-products, it is preferred for maintaining the acidic conditions needed for the oxidation reactions with \(KMnO_4\).

Detailed Example: Oxidation of \(H_2S\)

When using \(KMnO_4\) in an acidic medium provided by \(H_2SO_4\), the reaction can be:

\(2KMnO_4 + 10H_2S + 16H_2SO_4 \rightarrow 2MnSO_4 + 10S + 8H_2O\)

In this reaction, \(H_2S\) is oxidized to elemental sulfur (\(S\)), and \(KMnO_4\) is reduced to manganese sulfate (\(MnSO_4\)).

If \(HCl\) were used: The side reaction involving \(HCl\) would produce chlorine gas and consume \(KMnO_4\), making it unsuitable for reactions requiring precise and effective oxidation by \(KMnO_4\).

Summary

Sulfuric acid (\(H_2SO_4\)) is used in place of hydrochloric acid (\(HCl\)) when working with \(KMnO_4\) because \(HCl\) can be oxidized by \(KMnO_4\) to produce chlorine gas, which interferes with the oxidation process and consumes the oxidizing agent.

Sulfuric acid does not have this issue and provides a stable acidic medium for the oxidation reactions involving \(KMnO_4\). Thus, the correct reason is: 2. \(HCl\) is oxidized by \(KMnO_4\) to \(Cl_2\).