Problem 103 - A Complete Resource Book in Chemistry for JEE Main

Question

vIn which of the following reactions does ammonia act as an oxidizing agent? (a) \(3 \mathrm{NaClO}+2 \mathrm{NH}_{3} \longrightarrow 3 \mathrm{NaCl}+\mathrm{N}_{2}+3 \mathrm{H}_{2} \mathrm{O}\) (b) \(3 \mathrm{CaOCl}_{2}+2 \mathrm{NH}_{3} \longrightarrow 3 \mathrm{CaCl}_{2}+\mathrm{N}_{2}+3 \mathrm{H}_{2} \mathrm{O}\) (c) \(4 \mathrm{NH}_{3}+5 \mathrm{O}_{2} \longrightarrow 4 \mathrm{NO}+6 \mathrm{H}_{2} \mathrm{O}\) (d) none of these

Step-by-Step Solution

Answer

Option (d) - none of these.

Step 1: Understanding Oxidizing Agent

An oxidizing agent is a substance that gains electrons and is reduced in a chemical reaction. For ammonia to act as an oxidizing agent, it must gain electrons and its oxidation state must decrease.

Step 2: Analyzing Reaction (a)

In reaction (a), the ammonia (\(\text{NH}_3\)) transforms into \(\text{N}_2\). The oxidation state of nitrogen in \(\text{NH}_3\) is -3, while in \(\text{N}_2\) it is 0. Since the oxidation state of nitrogen increases, ammonia is not an oxidizing agent here.

Step 3: Analyzing Reaction (b)

In reaction (b), similar to reaction (a), ammonia (\(\text{NH}_3\)) changes to \(\text{N}_2\). Again, the oxidation state of nitrogen increases from -3 to 0, indicating ammonia is not acting as an oxidizing agent.

Step 4: Analyzing Reaction (c)

In reaction (c), ammonia (\(\text{NH}_3\)) is converted into \(\text{NO}\). The oxidation state of nitrogen in \(\text{NH}_3\) is -3 and in \(\text{NO}\) is +2. Since the oxidation state increases, ammonia is not an oxidizing agent in this case.

Step 5: Conclusion

Since in all reactions the oxidation state of nitrogen in ammonia increases rather than decreases, ammonia does not act as an oxidizing agent in any of the given reactions.

Key Concepts

Oxidizing Agents

In the world of chemistry, an oxidizing agent is a substance that accepts electrons during a chemical reaction. By doing so, it undergoes a reduction in its oxidation state. Oxidizing agents are critical in driving reactions where transfer of electrons is involved.
For a substance to act as an oxidizing agent, it needs to have the ability to accept electrons and, as a result, its own oxidation state decreases. This property is essential in processes such as combustion, rusting, and many biochemical reactions.

• Oxidizing agents are often of interest in redox reactions.
• The decrease in oxidation state is a hallmark of these agents.
• Common examples include oxygen, chlorine, and potassium dichromate.

Oxidation States

Oxidation states, often referred to as oxidation numbers, are a central concept in understanding redox reactions. They indicate the degree of oxidation of an atom within a molecule. This, in turn, affects the atom's tendency to donate or accept electrons in reactions.
The oxidation state is a positive or negative number assigned based on some rules:

• For a pure element, the oxidation state is always zero.
• In molecules like \( ext{NH}_3\), the sum of oxidation states must match the overall charge of the molecule.
• Each decrease in oxidation state means the substance might be a reducing agent.

To fully understand ammonia's role in the exercise reactions, it's crucial to determine how its nitrogen atom's oxidation state changes. In all studied reactions, the oxidation state of nitrogen in ammonia increased, confirming that ammonia acts as a reducing, not an oxidizing, agent in these scenarios.

Ammonia Reactions

Ammonia (\(\text{NH}_3\)) is a versatile and commonly encountered chemical compound in reactions. It can act as both a reducing agent and a source of nitrogen. Understanding the roles ammonia might play depends on the chemical environment and the substances it reacts with.
In the provided exercise, ammonia reacts in three scenarios:

• In reactions (a) and (b), ammonia transforms into nitrogen gas \(\text{N}_2\), showing an increase in oxidation state of nitrogen from -3 in \(\text{NH}_3\) to 0 in \(\text{N}_2\).
• In reaction (c), ammonia is oxidized to \(\text{NO}\), with nitrogen's oxidation state rising from -3 to +2.
• These state changes imply ammonia’s role as a reducing agent, with potential application in synthesis and industrial processes.

Ammonia’s transformative reactions underscore its role, not as an oxidizing agent here, but rather in facilitating electron transfer and contributing to new compound formation.