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Chapter 9: Problem 88

When \(\mathrm{PbO}_{2}\) reacts with conc. \(\mathrm{HNO}_{3}\), the gas evolved is: (a) \(\mathrm{NO}_{2}\) \(\square\) (b) \(\mathrm{O}_{2}\) (c) \(\mathrm{N}_{2}\) \(\square\) (d) \(\mathrm{N}_{2} \mathrm{O}\)

Short Answer

Expert verified
The gas evolved is \(\mathrm{NO}_2\).

Step by step solution

01

Understanding the Reaction

The given problem involves the reaction of lead dioxide \(\mathrm{PbO}_2\) with concentrated nitric acid \(\mathrm{HNO}_3\). We need to find the gas that is evolved from this reaction.
02

Write the Chemical Equation

The reaction between \(\mathrm{PbO}_2\) and \(\mathrm{HNO}_3\) produces lead(II) nitrate \(\mathrm{Pb(NO}_3)_2\), water \(\mathrm{H}_2\mathrm{O}\), and nitrogen dioxide gas \(\mathrm{NO}_2\). The balanced chemical equation is: \[ \mathrm{PbO}_2 + 4\mathrm{HNO}_3 \rightarrow \mathrm{Pb(NO}_3)_2 + 2\mathrm{NO}_2 + 2\mathrm{H}_2\mathrm{O} \]
03

Determine the Evolved Gas

From the balanced chemical equation, it is clear that the gas evolved in the reaction is \(\mathrm{NO}_2\), which is one of the products formed in the reaction.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

PbO2 and HNO3 Reaction
In this chemical reaction, we see how lead dioxide ( PbO_2 ) interacts with concentrated nitric acid ( HNO_3 ). Lead dioxide is an oxidizing agent, and HNO_3 is a common inorganic acid used in various chemical processes. When these substances react, they produce several compounds, including lead(II) nitrate ( Pb(NO_3)_2 ), water ( H_2O ), and nitrogen dioxide ( NO_2 ) gas. This type of reaction is quite important as it showcases the behavior of metal oxides with strong oxidizing acids.
In this specific reaction:
  • Lead dioxide ( PbO_2 ) is reduced and transformed into lead(II) nitrate ( Pb(NO_3)_2 ).
  • Nitric acid acts both as a reactant and an oxidizing agent, promoting the release of nitrogen dioxide gas.
  • The formation of gas makes this reaction visually interesting in a laboratory setting, often indicated by the brown fumes of NO_2 .
This reaction underlines the concept of redox processes where the breakdown of metal oxides leads to the liberation of gases.
Gas Evolution in Chemical Reactions
Gas evolution is a process in which a gas is released from a reaction, often making it visually observable. In the reaction between PbO_2 and HNO_3 , nitrogen dioxide ( NO_2 ) is evolved as a gas. This phenomenon helps chemists understand the progression and completion of a reaction.
When gases like NO_2 are evolved:
  • It can indicate the occurrence of a redox reaction.
  • The release can be tracked and used to deduce information about the reaction's stoichiometry and kinetics.
  • In the case of NO_2 , the gas is known for its distinctive brown color, which aids in visual detection.
Gas evolution not only serves as evidence of a chemical reaction but also provides insights into reaction thermodynamics and mechanisms.
Balanced Chemical Equations
A balanced chemical equation is crucial as it ensures the conservation of mass, complying with the law of conservation of matter. For the reaction between PbO_2 and HNO_3, the balanced equation is:\[PbO_2 + 4HNO_3 \rightarrow Pb(NO_3)_2 + 2NO_2 + 2H_2O\]
This equation is balanced because it correctly reflects the number of atoms of each element on both sides of the equation. Using a balanced equation allows chemists to:
  • Determine the correct stoichiometric ratios of reactants and products.
  • Predict the amounts of products formed from given amounts of reactants.
  • Understand the energy changes associated with the reaction.
Without balancing, one risks making incorrect conclusions about a reaction's requirements and products.
Reaction Mechanisms in Chemistry
Understanding reaction mechanisms鈥攖he step-by-step sequence of elementary reactions by which an overall chemical change occurs鈥攊s essential for predicting and controlling chemical behavior. In the PbO_2 and HNO_3 reaction, the mechanism involves the transfer of oxygen and nitrate groups.
Examining mechanisms helps us visualize:
  • The intermediate species formed during the reaction pathway.
  • Rate-determining steps that may influence the speed of the reaction.
  • The roles of catalysts, if any, which affect the efficiency of the reaction.
Through detailed study and examination of mechanisms, chemists can leverage knowledge to develop new methods for synthesis, improve industrial processes, and enhance understanding of complex biochemical pathways.

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