Problem 145 - A Complete Resource Book in Chemistry for JEE Main

Question

Four elements \(\mathrm{A}, \mathrm{B}, \mathrm{C}\) and \(\mathrm{D}\) can form diatomic molecules and monoatomic anions with \(-1\) charge. Consider the following reactions about these. \(2 \mathrm{~B}^{-}+\mathrm{C}_{2} \longrightarrow 2 \mathrm{C}^{-}+\mathrm{B}_{2}\) \(\mathrm{B}_{2}+2 \mathrm{D}^{-} \longrightarrow 2 \mathrm{~B}^{-}+\mathrm{D}_{2}\) \(2 \mathrm{~A}^{-}+\mathrm{C}_{2}\) no reaction Select correct statement about these. (1) \(\mathrm{A}_{2}\) is strongest oxidizing agent while \(\mathrm{D}\) is strongest reducing agent (2) \(\mathrm{D}_{2}\) is strongest oxidizing agent while \(\mathrm{A}\) is strongest reducing agent (3) \(\mathrm{C}_{2}\) will oxidize \(\mathrm{B}^{-}\)and also \(\mathrm{D}^{-}\)to form \(\mathrm{B}_{2}\) and \(\mathrm{D}_{2}\) (4) \(\mathrm{E}^{\circ} \mathrm{A}_{2} / \mathrm{A}^{-}\)is the lowest (a) 2 and 3 (b) 1 and 3 (c) 2 and 4 (d) 1,2 and 3

Step-by-Step Solution

Answer

The correct option is (c) 2 and 4.

Step 1: Understanding the Reaction Equations

To evaluate the reactions, let's first consider what happens in each provided reaction. 1. In the reaction \(2 \mathrm{B}^{-} + \mathrm{C}_{2} \rightarrow 2 \mathrm{C}^{-} + \mathrm{B}_{2}\), \(\mathrm{C}_{2}\) oxidizes \(\mathrm{B}^{-}\) to form \(\mathrm{B}_{2}\) and \(\mathrm{C}^{-}\). Here, \(\mathrm{C}_{2}\) acts as an oxidizing agent, and \(\mathrm{B}^{-}\) as a reducing agent. 2. In the reaction \(\mathrm{B}_{2} + 2 \mathrm{D}^{-} \rightarrow 2 \mathrm{B}^{-} + \mathrm{D}_{2}\), \(\mathrm{D}^{-}\) reduces \(\mathrm{B}_{2}\) back to \(\mathrm{B}^{-}\), forming \(\mathrm{D}_{2}\). \(\mathrm{D}^{-}\) acts as a reducing agent in this reaction. 3. \(2 \mathrm{A}^{-} + \mathrm{C}_{2}\) shows no reaction, indicating \(\mathrm{A}^{-}\) is not strong enough to reduce \(\mathrm{C}_{2}\). This implies \(\mathrm{A}^{-}\) is a weaker reducing agent compared to \(\mathrm{B}^{-}\).

Step 2: Assessing Species as Oxidizing and Reducing Agents

Based on the above reactions:- \(\mathrm{C}_{2} \) is a stronger oxidizing agent than \(\mathrm{D}_{2}\) because it can oxidize both \( \mathrm{B}^{-} \) and potentially reduce further to \(\mathrm{C}^{-}\). - \(\mathrm{D}_{2}\) must then be a stronger oxidizing agent than \(\mathrm{A}_{2}\) because \(\mathrm{A}_{2}\) can't oxidize \(\mathrm{C}^{-}\). - \(\mathrm{D}^{-}\) proves to be a stronger reducing agent than \(\mathrm{A}^{-}\), as \(\mathrm{A}^{-}\) doesn't bring about any reaction. Hence, \(\mathrm{D}\) also stands as a strong reducing agent.

Step 3: Evaluating Each Statement

(1) \(\mathrm{A}_{2}\) isn't proven to be the strongest oxidizing agent—\(\mathrm{D}_{2}\) would actually be stronger. (2) True: \(\mathrm{D}_{2}\) being stronger than \(\mathrm{A}_{2}\) as an oxidizing agent and \(\mathrm{A}\) being a weak reducing agent matches what we know.(3) \(\mathrm{C}_{2}\) already oxidizes \(\mathrm{B}^{-}\), and given its behavior, it can oxidize \(\mathrm{D}^{-}\) too.(4) \(\mathrm{A}_{2}\)'s electrode potential being lowest supports \(\mathrm{A}^{-}\) as having the least reducing potential.

Step 4: Select the Correct Answer

Given our analysis, statements 2, 3, and 4 hold true based on the reactions and assessed strength of oxidizing/reducing agents, corresponding to option (c) 2 and 4. Since \(\mathrm{C}_{2}\) oxidizes both \(\mathrm{B}^{-}\) and potentially \(\mathrm{D}^{-}\), combinations confirming these findings align.

Key Concepts

Oxidizing Agents

In chemistry, an oxidizing agent is a substance that increases oxidation in other substances by accepting electrons. Essentially, it "oxidizes" the other chemical species. In the provided reaction equations, we observe that:

• \(C_2\) acts as an oxidizing agent when it converts \(B^-\) to \(B_2\) by accepting electrons and forming \(C^-\).
• Another observed oxidizing agent in the reactions is \(D_2\), which is stronger than \(A_2\), since \(A_2\) doesn’t cause a reaction with \(C_2\).

This characteristic helps us determine and compare the strength of oxidizing agents. The stronger the oxidizing agent, the more it tends to acquire electrons and bring about oxidation.
It's significant to note that the ability to act as an oxidizing agent is critical in determining how these reactions proceed. Understanding the role of these agents is essential for evaluating different chemical processes.

Reducing Agents

Reducing agents are substances that donate electrons to another species. This process is known as reduction. The reducing agent itself gets oxidized in the process. In our reactions, we find:

• \(B^-\) is a reducing agent in the reaction \(2B^- + C_2 \rightarrow 2C^- + B_2\), where it donates electrons and gets oxidized to form \(B_2\).
• \(D^-\) serves as a reducing agent in the reaction \(B_2 + 2D^- \rightarrow 2B^- + D_2\), demonstrating its ability by donating electrons and reducing \(B_2\) back to \(B^-\).

Interestingly, \(A^-\) is noted as a weaker reducing agent. This is inferred from its inability to facilitate a reaction with \(C_2\). Thus, \(D^-\) stands out as a stronger reducing agent compared to \(A^-\).
Understanding the concept of reducing agents assists in comprehending how electrons are transferred during chemical reactions, which is vital for predicting the outcome of such reactions.

Electrode Potential

Electrode potential, often represented as \(E^0\), is a measure of a substance's tendency to gain or lose electrons. This potential is crucial in deciding the direction and feasibility of redox (reduction-oxidation) reactions.

• In our context, the electrode potential of \(A_2/A^-\) is the lowest among the species, suggesting it has the least tendency to act as an oxidizing agent.
• Furthermore, since \(C_2\) has demonstrated a strong capacity to oxidize \(B^-\) and even potentially \(D^-\), its electrode potential is higher than that of \(A_2\).

It's important to know that a higher electrode potential indicates a greater ability to act as an oxidizing agent, as seen in \(C_2\) and \(D_2\).
Evaluating electrode potentials is a fundamental aspect of understanding the push and pull of electrons in redox reactions, crucial for predicting which reactions are feasible.

Reaction Equations

Reaction equations depict the transformation of reactant molecules to products, detailing the conservation of atoms and charge. In analyzing our given reaction equations, we uncover insights about the roles of each element:

• The equation \(2B^- + C_2 \rightarrow 2C^- + B_2\) shows that \(C_2\) oxidizes \(B^-\) to \(B_2\), alongside the reduction of \(C_2\) to \(C^-\).
• In \(B_2 + 2D^- \rightarrow 2B^- + D_2\), \(D^-\) reduces \(B_2\) back to \(B^-\), indicating a redox process.
• Finally, there is no reaction between \(2A^-\) and \(C_2\), reflecting chemical inertness in this instance.

Interpreting these equations helps us predict the role of each substance in a reaction process. It’s through these written representations that we can deduce the dynamics of oxidizing and reducing agents, as well as reaction feasibility and outcomes.