Problem 64 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

\(\mathrm{Mn}^{2+}\) can be oxidised to \(\mathrm{Mn} \mathrm{O}_{4}^{-}\)by \(\ldots \ldots \ldots \ldots \ldots .\) \(\left(\mathrm{SnO}_{2}, \mathrm{PbO}_{2}, \mathrm{BaO}_{2}\right)\)

Step-by-Step Solution

Answer

PbO2 can oxidize Mn2+ to MnO4-.

Step 1: Identify the Problem

The problem asks which compound among SnO2, PbO2, and BaO2 can oxidize Mn2+ to MnO4-. This requires knowing which of these compounds is a strong enough oxidizing agent.

Step 2: Understand the Oxidation Potential

A suitable oxidizing agent must have a higher oxidation potential than the MnO_4^- / Mn2+ redox couple. The Mn2+ to MnO4- oxidation requires an oxidizing agent with a sufficient standard reduction potential to drive the reaction.

Step 3: Compare Standard Reduction Potentials

The standard reduction potential for \[ \mathrm{MnO}_{4}^{-} + 8 \mathrm{H}^{+} + 5 \mathrm{e}^{-} \rightarrow \mathrm{Mn}^{2+} + 4 \mathrm{H}_{2}\mathrm{O}\]is +1.51 V. We need a compound that can provide oxidation potential greater than this to oxidize Mn2+ to MnO4-.

Step 4: Analyze the Compounds

Among the options given: - \( \mathrm{SnO}_{2} \) has a lower oxidation potential and is less likely to act as a strong oxidizing agent.- \( \mathrm{BaO}_{2} \) is a peroxide and usually unlikely to participate in such higher oxidation state transitions.- \( \mathrm{PbO}_{2} \) is known for its strong oxidizing properties with a potential that can drive the oxidation of Mn2+ to MnO4-.

Step 5: Final Selection and Justification

PbO2 has a high standard reduction potential, capable of oxidizing Mn2+ to MnO4-. Thus, PbO2 is the correct oxidizing agent for this transformation.

Key Concepts

Standard Reduction Potential

Standard reduction potential is a vital concept in understanding oxidation-reduction (redox) reactions. It represents a compound's ability to gain electrons, hence being reduced. Each redox reaction involves two half-reactions: reduction and oxidation.
Learning how to read and compare these potentials helps predict the direction of a redox reaction.

• The standard reduction potential is measured in volts (V) under standard conditions (25°C, 1 M concentrations, and 1 atm pressure).
• A higher reduction potential indicates a greater tendency for a substance to be reduced or act as an oxidizing agent.
• Conversely, a lower reduction potential suggests it is more likely to lose electrons, thus being oxidized.

In the exercise, the reduction potential of the \[ ext{MnO}_4^- / ext{Mn}^{2+} \]redox couple is crucial as the agent with a higher reduction potential than this couple can effectively oxidize \( ext{Mn}^{2+} \) to \( ext{MnO}_4^- \). Here, \( ext{PbO}_2 \) was chosen because its strong reduction potential matches the requirement.

Oxidizing Agents

Oxidizing agents play a key role in redox reactions by accepting electrons. These agents are themselves reduced in the process while causing the oxidation of another species. Identifying the right oxidizing agent means understanding its effectiveness, often measured by its standard reduction potential.
Common characteristics of strong oxidizing agents include:

• High standard reduction potential.
• Ability to accept electrons readily.
• The presence of elements in high oxidation states.

For instance, in the problem, determining which compound could oxidize \( ext{Mn}^{2+} \) to \( ext{MnO}_4^- \) required evaluating the oxidizing strengths of \( ext{SnO}_2 \), \( ext{PbO}_2 \), and \( ext{BaO}_2 \). Out of these, \( ext{PbO}_2 \) proved to be the strongest due to its favorable reduction potential, allowing it to facilitate the oxidation process effectively.

Redox Chemistry

Redox chemistry focuses on the study of oxidation-reduction reactions. This area of chemistry is essential for understanding how substances interact by transferring electrons. Redox reactions are present in many processes, from metabolic pathways to industrial applications.
Key aspects of redox chemistry include:

• Each redox reaction consists of two half-reactions: one representing oxidation and the other reduction.
• Oxidation is the process of losing electrons, whereas reduction involves gaining electrons.
• The balance of electrons is fundamental; the number lost must equal the number gained.

In our exercise, the oxidation of \( ext{Mn}^{2+} \) to \( ext{MnO}_4^- \) involves a transfer of electrons enabled by a suitable oxidizing agent. Understanding redox chemistry, specifically balancing the half-reactions and seeking agents with adequate standard reduction potentials, is critical to predicting and facilitating these reactions successfully.