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. \(2 \mathrm{~B}+\mathrm{C}_{2} \longrightarrow 2 \mathrm{C}^{-}+\mathrm{B}_{2}\) \(\mathrm{B}_{2}+2 \mathrm{D} \longrightarrow{\longrightarrow}{\longrightarrow} \mathrm{B}^{-}+\mathrm{D}_{2}\) \(2 \mathrm{~A}^{-}+\mathrm{C}_{2}\) 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) \(\mathrm{E}^{\mathrm{O}} \mathrm{A}_{2} / \mathrm{A}^{-}\)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

Option (b) 1 and 3 are correct statements about these reactions.

Step 1: Understanding the Problem

We have 4 elements, A, B, C, and D, that can form diatomic molecules and monoatomic anions with a -1 charge. We need to analyze the given reactions to determine which statements about the oxidizing and reducing agents are correct.

Step 2: Analyzing Reaction 1

The reaction given is \(2 \mathrm{B} + \mathrm{C}_{2} \longrightarrow 2 \mathrm{C}^{-} + \mathrm{B}_{2}\). In this reaction, \(\mathrm{C}_{2}\) is being reduced to \(\mathrm{C}^{-}\) and \(\mathrm{B}\) is being oxidized to \(\mathrm{B}_{2}\). This implies \(\mathrm{C}_{2}\) is an oxidizing agent and \(\mathrm{B}\) is a reducing agent.

Step 3: Analyzing Reaction 2

The reaction here is \(\mathrm{B}_{2} + 2 \mathrm{D} \longrightarrow \mathrm{B}^{-} + \mathrm{D}_{2}\). In this reaction, \(\mathrm{D}\) is oxidized to \(\mathrm{D}_{2}\) and \(\mathrm{B}_{2}\) is reduced to \(\mathrm{B}^{-}\). \(\mathrm{B}_{2}\) is the oxidizing agent and \(\mathrm{D}\) is the reducing agent.

Step 4: Analyzing Reaction 3

The given condition is that \(\mathrm{A}^{-}\) and \(\mathrm{C}_{2}\) do not react. This implies that \(\mathrm{A}^{-}\) cannot reduce \(\mathrm{C}_{2}\), suggesting that \(\mathrm{A}^{-}\) does not act as a stronger reducing agent than \(\mathrm{B}\) or \(\mathrm{D}\).

Step 5: Evaluating Option 1

\(\mathrm{A}_{2}\) being the strongest oxidizing agent contradicts the reaction information because it doesn't react with \(\mathrm{C}_{2}\). Likewise, \(\mathrm{D}\) being the strongest reducing agent fits because it reduces \(\mathrm{B}_{2}\).

Step 6: Evaluating Option 2

This option states \(\mathrm{D}_{2}\) is the strongest oxidizing agent and \(\mathrm{A}\) is the strongest reducing agent. This contradicts the reaction observations, as \(\mathrm{D}_{2}\) is formed and does not oxidize anything itself, and \(\mathrm{A}\) is not able to reduce \(\mathrm{C}_{2}\).

Step 7: Evaluating Option 3

This statement claims \(\mathrm{C}_{2}\) can oxidize \(\mathrm{B}^{-}\) and \(\mathrm{D}^{-}\) to form \(\mathrm{B}_{2}\) and \(\mathrm{D}_{2}\). The given reaction already supports the conversion of \(\mathrm{B}\) by \(\mathrm{C}_{2}\); therefore this statement is at least partially correct.

Step 8: Evaluating Option 4

Evaluating this option requires understanding that \(\mathrm{E}^{O} (\mathrm{A}_{2}/\mathrm{A}^{-})\) needs context. Previous steps suggest it's not significant enough to claim it has the lowest potential when \(\mathrm{A}^{-}\) doesn't reduce \(\mathrm{C}_{2}\). It implies \(\mathrm{A}^{-}\) is not a strong reducing agent.

Key Concepts

Oxidizing Agents

When discussing chemical reactions, particularly redox (or reduction-oxidation) reactions, an oxidizing agent plays a vital role. An oxidizing agent gains electrons in the process of a redox reaction. This means that the oxidizing agent essentially "steals" electrons from other substances, causing those substances to be oxidized.
In our example reactions,

• In Reaction 1, the molecule \( \mathrm{C}_{2} \) is an example of an oxidizing agent. It undergoes a transformation to \( \mathrm{C}^{-} \) by gaining electrons, indicating its role as the oxidizing agent.
• In Reaction 2, \( \mathrm{B}_{2} \) serves as an oxidizing agent, as it gains electrons from \( \mathrm{D} \) and transforms into \( \mathrm{B}^{-} \).

The key takeaway is that oxidizing agents are crucial as they drive the oxidation process by acquiring electrons. Knowing this helps in identifying which substances in a reaction can act as oxidizing agents.

Reducing Agents

Reducing agents are substances that donate electrons in a redox reaction. Think of them as the opposite of oxidizing agents. A reducing agent loses electrons, which are then gained by another substance, thus causing the latter to be reduced.
Let's consider the reactions provided:

• In Reaction 1, \( \mathrm{B} \) acts as the reducing agent because it donates electrons to \( \mathrm{C}_{2} \), leading to its oxidation to \( \mathrm{B}_{2} \).
• In Reaction 2, \( \mathrm{D} \) donates electrons to \( \mathrm{B}_{2} \), getting oxidized to \( \mathrm{D}_{2} \), which shows \( \mathrm{D} \)’s role as a reducing agent.

Understanding reducing agents is essential in grasping how electron transfer occurs in reactions. Each reducing agent plays its role by losing electrons, which is a critical process for enabling reduction to happen in another substance.

Redox Reactions

Redox reactions are a type of chemical reaction where oxidation and reduction simultaneously occur. These reactions are essential in many biological and chemical processes. In every redox reaction, there is a transfer of electrons between two substances.
In the given exercise,

• Reaction 1 involves \( \mathrm{C}_{2} \) being reduced to \( \mathrm{C}^{-} \) and \( \mathrm{B} \) being oxidized to \( \mathrm{B}_{2} \).
• Reaction 2 demonstrates how \( \mathrm{B}_{2} \) is reduced to \( \mathrm{B}^{-} \) while \( \mathrm{D} \) is oxidized to \( \mathrm{D}_{2} \).

The redox process is integral to maintaining the balance of electron transfer throughout these reactions. Comprehending redox reactions involves observing how electrons are moved and identifying which substances undergo oxidation or reduction. This understanding helps one predict and manipulate reaction outcomes effectively.