Problem 91 - A Complete Resource Book in Chemistry for JEE Main

Question

In which of the following reactions ozone acts as an oxidizing agent? (1) \(2 \mathrm{HCl}+\mathrm{O}_{3} \longrightarrow \mathrm{Cl}_{2}+\mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}\) (2) \(\mathrm{BaO}_{2}+\mathrm{O}_{3} \longrightarrow \mathrm{BaO}+2 \mathrm{O}_{2}\) (3) \(2 \mathrm{KI}+\mathrm{O}_{3}+\mathrm{H}_{2} \mathrm{O} \longrightarrow 2 \mathrm{KOH}+\mathrm{I}_{2}+\mathrm{O}_{2}\) (4) \(\mathrm{PbS}+4 \mathrm{O}_{3} \longrightarrow \mathrm{PbSO}_{4}+4 \mathrm{O}_{2}\) (a) 1,2 and 4 (b) 2 and 3 (c) 1,3 and 4 (d) 1 and 2

Step-by-Step Solution

Answer

Ozone acts as an oxidizing agent in reactions 1, 3, and 4. Correct answer: (c) 1, 3 and 4.

Step 1: Understanding Oxidizing Agents

An oxidizing agent is a substance that gains electrons and, in the process, oxidizes another substance. In this context, we need to identify where ozone \(O_3\) is gaining electrons or, in chemical terms, being reduced.

Step 2: Analyze Reaction 1

Reaction: \(2 \mathrm{HCl}+\mathrm{O}_{3} \longrightarrow \mathrm{Cl}_{2}+\mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}\). In this reaction, \(\mathrm{O}_3\) is reduced to \(\mathrm{O}_2\), while \(\mathrm{Cl}^-\) ions are oxidized to \(\mathrm{Cl}_2\). Thus, \(\mathrm{O}_3\) acts as an oxidizing agent.

Step 3: Analyze Reaction 2

Reaction: \(\mathrm{BaO}_{2}+\mathrm{O}_{3} \longrightarrow \mathrm{BaO}+2 \mathrm{O}_{2}\). Here, \(\mathrm{O}_3\) is decomposed into \(\mathrm{O}_2\) without gaining electrons from another element as \(\mathrm{BaO}_2\) is unchanging in oxidation state, meaning \(\mathrm{O}_3\) is not acting as an oxidizing agent.

Step 4: Analyze Reaction 3

Reaction: \(2 \mathrm{KI}+\mathrm{O}_{3}+\mathrm{H}_{2} \mathrm{O} \longrightarrow 2 \mathrm{KOH}+\mathrm{I}_{2}+\mathrm{O}_{2}\). Here, iodine \(\mathrm{I}^-\) from KI is oxidized to \(\mathrm{I}_2\), indicating that \(\mathrm{O}_3\) is acting as an oxidizing agent, by reducing to \(\mathrm{O}_2\).

Step 5: Analyze Reaction 4

Reaction: \(\mathrm{PbS}+4 \mathrm{O}_{3} \longrightarrow \mathrm{PbSO}_{4}+4 \mathrm{O}_{2}\). Sulfur in \(\mathrm{PbS}\) is oxidized to sulfate \(\mathrm{SO}_4^{2-}\), indicating \(\mathrm{O}_3\) is a good oxidizing agent here as it gets reduced to \(\mathrm{O}_2\).

Step 6: Compare Observations

Reactions 1, 3, and 4 all show \(\mathrm{O}_3\) gaining electrons and oxidizing another substance (acting as an oxidizing agent). Reaction 2 does not, as \(\mathrm{O}_3\) decomposes without electron exchange.

Key Concepts

Chemical Reactions

Chemical reactions are processes where substances, known as reactants, are transformed into new substances called products. These reactions involve the breaking and forming of bonds between atoms. The conservation of mass law means that the total mass of reactants equals the total mass of products. Additionally, chemical reactions follow specific patterns or types, such as synthesis, decomposition, single replacement, and double replacement reactions.

The understanding of chemical reactions is fundamental, as it allows us to predict the outcome of combining substances. For example, in this exercise, we are examining different reactions to see when ozone acts as an oxidizing agent. Recognizing the type of reaction helps in anticipating whether or not a reactant will undergo oxidation or reduction. This foresight is crucial, especially in redox reactions, where the transfer of electrons plays a key role.

Knowing about chemical reactions can be practically applied, from forming new materials to applications in industries and everyday life processes like respiration and combustion. This concept lays the groundwork for further topics such as redox reactions and the role of oxidizing agents.

Oxidizing Agents

An oxidizing agent, also known as an oxidant, is a substance that has the ability to oxidize other substances. This means the oxidizing agent gains electrons in a chemical reaction, which causes another element to lose electrons. Often, oxidizing agents are elements with high electronegativity or a high oxidation number.

In the context of our exercise, ozone ( O_3 ) acts as an oxidizing agent. As it reacts, ozone is reduced while causing another substance to gain oxygen or lose electrons. For example, in the reaction with hydrogen chloride ( HCl ), ozone is instrumental in transforming chloride ions into chlorine gas, demonstrating its role as an oxidant.

Ozone's role as an oxidizing agent is beneficial due to its ability to break down pollutants and kill microorganisms. Its powerful oxidizing capabilities make it useful in applications such as water purification and air treatment. Understanding the nature and function of oxidizing agents offers insights into their ubiquitous role in both biological and industrial processes.

Reduction and Oxidation (Redox) Reactions

Redox reactions are a type of chemical reaction involving the transfer of electrons between two substances. These reactions consist of two half-reactions: one that involves oxidation and one that involves reduction. In essence, oxidation involves the loss of electrons, whereas reduction involves the gain of electrons.

These reactions are fundamental in various chemical, biological, and industrial processes. In the exercise provided, understanding redox reactions allows us to see how ozone acts as an oxidizing agent. By examining each reaction, such as ozone reducing to dioxygen ( O_2 ), we can understand how it enables other reactants like iodine and sulfur to oxidize. This ability to identify electrons transfer processes is crucial in determining whether a reaction is a redox reaction.

Redox reactions are also widely used in energy applications, such as in batteries and fuel cells, where electron transfer is harnessed for power. This concept covers a broad range of chemical activities and is vital for understanding deeper chemical insights and innovations.