Problem 14 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Given : \(E_{\mathrm{Cr}^{3+} / \mathrm{Cr}}^{\circ}=-0.74 \mathrm{~V} ; \mathrm{E}_{\mathrm{MnO}_{4}^{-} / \mathrm{Mn}^{2+}}^{\circ}=1.51 \mathrm{~V}\) \(\mathrm{E}_{\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-} / \mathrm{Cr}^{3+}}=1.33 \mathrm{~V} ; \mathrm{E}_{\mathrm{Cl} / \mathrm{Cl}^{-}}^{\circ}=1.36 \mathrm{~V}\) Based on the data given above, strongest oxidising agent will be : [Main 2013] (a) \(\mathrm{Cl}\) (b) \(\mathrm{Cr}^{3+}\) (c) \(\mathrm{Mn}^{2+}\) (d) \(\mathrm{Mn} \mathrm{O}_{4}\)

Step-by-Step Solution

Answer

The strongest oxidizing agent is MnO4^- (Option d).

Step 1: Understanding Oxidation Potentials

In electrochemistry, the standard electrode potential ( E° ) is a measure of the tendency of a chemical species to be reduced. The more positive the E° value, the stronger the oxidizing agent, as it has a higher tendency to gain electrons.

Step 2: List Given Potentials

We are given the standard potentials: E°_{ ext{Cr}^{3+}/ ext{Cr}} = -0.74 ext{ V} , E°_{ ext{MnO}_4^{-}/ ext{Mn}^{2+}} = 1.51 ext{ V} , E°_{ ext{Cr}_2 ext{O}_7^{2-}/ ext{Cr}^{3+}} = 1.33 ext{ V} , E°_{ ext{Cl}/ ext{Cl}^{-}} = 1.36 ext{ V} .

Step 3: Identifying the Strongest Oxidizing Agent

From the given data, compare each potential. The strongest oxidizing agent will have the highest standard reduction potential. Let's compare: 1.51 ext{ V} (MnO_4^-), 1.36 ext{ V} (Cl_2), 1.33 ext{ V} (Cr_2O_7^{2-}), and -0.74 ext{ V} (Cr^{3+}).

Step 4: Conclusion

Among the given potentials, E°_{ ext{MnO}_4^{-}/ ext{Mn}^{2+}} = 1.51 ext{ V} is the highest. Thus, MnO_4^- is the strongest oxidizing agent.

Key Concepts

Oxidizing Agents

Oxidizing agents play a crucial role in electrochemistry. They are substances that gain electrons during a chemical reaction, causing another substance to lose electrons (to be oxidized).
The effectiveness of an oxidizing agent is determined by how easily it can gain electrons and be reduced. In essence, a strong oxidizing agent has a higher tendency to undergo reduction, signified by a more positive standard electrode potential (E°).
Such agents are vital in redox reactions, as they drive the process of electron transfer. During these reactions, the oxidizing agent is reduced, moving to a lower oxidation state. Examples include substances like \( MnO_4^- \), \( Cl_2 \), or \( Cr_2O_7^{2-} \), which can readily accept electrons in reactions.
Understanding the strength and behavior of oxidizing agents is essential for predicting the outcome of redox reactions. It is their potential to drive these reactions that validates their importance in both Chemistry and industrial applications.

Electrode Potential

In electrochemistry, the electrode potential is a measure of the ability of a chemical species to be reduced or oxidized. Standard electrode potential, represented as \( E° \), is a key concept. It represents the voltage (in volts) under standard conditions when a species is being reduced.
This value is crucial as it helps predict the direction of electron flow in electrochemical cells. More positive values of electrode potential indicate a greater likelihood of reduction. For example, \( MnO_4^- / Mn^{2+} \) has an \( E° \) of 1.51 V, showing a strong tendency for reduction.
The electrode potential is used to calculate the cell potential and is vital in constructing galvanic cells. It provides insightful data on the energetic feasibility of reactions, helping chemists design processes for efficient energy conversion.

Reduction Potentials

Reduction potentials are numerical values that indicate the tendency of a chemical species to gain electrons and be reduced. These are often the central focus for comparing the relative strength of various oxidizing agents.
Reduction potential is indicated by \( E° \), with more positive values representing a greater ease of being reduced. For instance, in the given exercise, \( MnO_4^- \) has the highest reduction potential at 1.51 V, making it the strongest oxidizing agent compared to the others listed.
In practical terms, reduction potentials enable the prediction of which reactions are likely to occur spontaneously. They serve as a guide to understanding how different species will interact in a redox scenario.

• A higher reduction potential means a species will tend to gain electrons easily.
• A lower reduction potential suggests less tendency to accept electrons.

These insights are invaluable for chemists working with electrochemical cells, batteries, and similar technologies.