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) \(\mathrm{N}_{2}\)

Short answer

The gas liberated is \( \mathrm{NO}_2 \) (option a).

Step-by-step solution

Understanding the Reaction

First, we need to understand what occurs when lead dioxide (\( \mathrm{PbO}_2 \) reacts with concentrated nitric acid (\( \mathrm{HNO}_3 \). \(\mathrm{PbO}_2\) is an oxidizing agent and can decompose \(\mathrm{HNO}_3\) into different products.

Predicting Reaction Products

When strong oxidizing agents like \( \mathrm{PbO}_2 \) react with \( \mathrm{HNO}_3 \), nitrogen dioxide (\( \mathrm{NO}_2 \)) is often produced along with \( \mathrm{Pb(NO_3)_2} \) and water.

Identifying the Gas

Among the potential gases listed (\( \mathrm{NO}_2 \), \( \mathrm{O}_2 \), \( \mathrm{N}_2 \mathrm{O} \), \( \mathrm{N}_2 \)), \( \mathrm{NO}_2 \) is consistent with common reactions of \( \mathrm{PbO}_2 \) with concentrated \( \mathrm{HNO}_3 \) due to its oxidizing capabilities.

Write the Balanced Equation

The reaction can be balanced as follows:\[ \mathrm{PbO}_2 + 4 \mathrm{HNO}_3 \rightarrow \mathrm{Pb(NO_3)_2} + 2 \mathrm{H_2O} + \mathrm{2NO_2} \] This confirms that \( \mathrm{NO}_2 \) is the gas released.

Key concepts

Lead Dioxide Reactions

Lead dioxide (\( \mathrm{PbO}_2 \)) is a noteworthy compound in inorganic chemistry, primarily due to its powerful properties as an oxidizer. When analysing the interaction between lead dioxide and other chemicals, such as concentrated nitric acid (\( \mathrm{HNO}_3 \)), students must appreciate the nature of reactions lead dioxide can undergo. Lead dioxide can induce a chain of interesting reactions due to its ability to accept electrons from other substances, effectively causing them to lose electrons. This behavior classifies it as an oxidizing agent, capable of converting stronger acids and even releasing gases upon reaction. Understanding these interactions is critical when trying to predict reaction outcomes, particularly because \( \mathrm{PbO}_2 \) can decompose various compounds, leading to a broad spectrum of products.

Oxidizing Agents

Oxidizing agents are substances that can accept electrons from other reactants in a chemical reaction. In the context of our reaction between lead dioxide and concentrated nitric acid (\( \mathrm{HNO}_3 \)), lead dioxide plays the role of an oxidizing agent.Here's what makes an oxidizing agent so effective:

• They typically contain elements in high oxidation states.
• They drive the oxidation of other substances, themselves experiencing reduction.
• They are pivotal in both industrial and laboratory chemical reactions.

In \( \mathrm{PbO}_2 \)'s reaction with \( \mathrm{HNO}_3 \), the lead dioxide facilitates the transformation, essentially by oxidizing nitrogen in the nitric acid to produce nitrogen dioxide \( \mathrm{NO}_2 \). Recognizing how oxidizing agents function can help students understand various industrial processes, including the production of important compounds and gases.

Nitrogen Dioxide Formation

The formation of nitrogen dioxide (\( \mathrm{NO}_2 \)) is a key aspect of the outlined reaction between lead dioxide and concentrated nitric acid. Within the chemical equation \( \mathrm{PbO}_2 + 4 \mathrm{HNO}_3 \rightarrow \mathrm{Pb(NO_3)_2} + 2 \mathrm{H_2O} + 2\mathrm{NO}_2 \), nitrogen dioxide emerges as a reddish-brown gas. Understanding its formation can shed light on its role in reactions and its broader environmental impact.Nitrogen dioxide is significant for several reasons:

• It is an important intermediate in the synthesis of nitric acid and fertilizers.
• It is a potent air pollutant contributing to environmental and health concerns.
• It can further react within the atmosphere to form other nitrogenous compounds known as nitrogen oxides (NOx).

By grasping the formation and properties of \( \mathrm{NO}_2 \), students can understand its relevance in both natural and human-made atmospheric processes.