Problem 69 - A Complete Resource Book in Chemistry for JEE Main

Question

The gas which is liberated when \(\mathrm{PbO}_{2}\) reacts with concentrated \(\mathrm{HNO}_{3}\) (a) \(\mathrm{NO}_{2}\) (b) \(\mathrm{O}_{2}\) (c) \(\mathrm{N}_{2} \mathrm{O}\) (d) \(\mathrm{N}_{2}\)

Step-by-Step Solution

Answer

(a) \( \mathrm{NO}_{2} \) is the gas liberated when \( \mathrm{PbO}_{2} \) reacts with concentrated \( \mathrm{HNO}_{3} \).

Step 1: Understand the Reactants

We are starting with a reaction between lead dioxide \( \mathrm{PbO}_{2} \) and concentrated nitric acid \( \mathrm{HNO}_{3} \). The question asks which gas is liberated during this reaction.

Step 2: Reaction and Products

The possible products of this reaction include nitrous gas and oxygen gas, among others, depending on the conditions and the stoichiometry of the reactants.

Step 3: Analyze Likely Reactions

In concentrated \( \mathrm{HNO}_{3} \), \( \mathrm{NO}_{2} \) is a common gas formed because nitric acid acts as an oxidizing agent. It tends to produce nitrogen dioxide, which is a brown gas with a pungent odor.

Step 4: Identify the Correct Gas

Given the nature of concentrated \( \mathrm{HNO}_{3} \) and its reaction with \( \mathrm{PbO}_{2} \), the most likely gaseous product is \( \mathrm{NO}_{2} \). This aligns with the oxidizing properties of \( \mathrm{HNO}_{3} \).

Key Concepts

Oxidation-Reduction Reactions

When it comes to chemical reactions, oxidation-reduction reactions, often referred to as redox reactions, display the transfer of electrons between substances. These reactions are crucial as they showcase how elements change their oxidation states, revealing their tendency to either gain or lose electrons.

• Oxidation involves the loss of electrons, leading to an increase in oxidation state.
• Reduction, on the other hand, indicates a gain in electrons, resulting in a decrease in oxidation state.

In a typical redox reaction, one element or compound donates electrons (is oxidized) while another accepts those electrons (is reduced). This electron movement is what drives the reaction forward.
In the context of the given exercise, when lead dioxide (\(\mathrm{PbO}_{2}\)) reacts with concentrated nitric acid (\(\mathrm{HNO}_{3}\)), the nitric acid acts as a powerful oxidizing agent, facilitating these electron transfers and altering oxidation states.
These reactions are not only fascinating from a chemical standpoint but also vital in numerous applications such as batteries, corrosion processes, and many biological systems.

Lead Dioxide Reactions

Lead dioxide (\(\mathrm{PbO}_{2}\)) is a strong oxidizing agent in its own right. It means that it enjoys a significant ability to accept electrons from substances that must lose electrons (reducing agents). When subjected to reactions with other chemicals, lead dioxide often participates in redox processes.
In the reaction with concentrated nitric acid, \(\mathrm{PbO}_{2}\) is mixed as a part of a potentially complex redox system:

• Lead dioxide forms a component of electrodes in lead-acid batteries.
• Involvement in some types of glass and ceramics for its beneficial properties.

However, more pertinent to our discussion is the role of lead dioxide in reactions that result in gas liberation. When \(\mathrm{PbO}_{2}\) interacts with concentrated \(\mathrm{HNO}_{3}\), it forms \(\mathrm{NO}_{2}\), showcasing how these reactions often lead to the release of different gases depending on their conditions and the presence of oxidizing agents like \(\mathrm{HNO}_{3}\).
This showcases lead dioxide’s versatility and importance in various chemical reactions, including gas liberation.

Nitric Acid Properties

Nitric acid (\(\mathrm{HNO}_{3}\)) is known for its powerful oxidizing properties, which makes it a significant agent in many chemical reactions, especially in redox ones. As a strong acid, it has the potential to participate in more than just simple neutralization reactions.
Some key features of nitric acid include:

• Oxidation Properties: It can convert substances, particularly metals, from lower to higher oxidation states, a capability it demonstrates in its interaction with lead dioxide.
• Reactivity: Concentrated nitric acid reacts with metals and nonmetals alike, often producing nitrogen oxides. In the case of the reaction with \(\mathrm{PbO}_{2}\), \(\mathrm{NO}_{2}\) is usually the resultant gaseous product.
• Common Applications: Beyond laboratory reactions, \(\mathrm{HNO}_{3}\) is valuable in manufacturing explosives, fertilizers, and in metal processing.

Its quality as a corrosive and oxidizing agent makes nitric acid invaluable, but also requires careful handling to ensure safety in its use. Its reactivity profile showcases not only its vigor but also how it can transform substances in significant ways through redox reactions, like liberating nitrogen dioxide gas when reacting with compounds like \(\mathrm{PbO}_{2}\).