Problem 28 - Chemistry in 30 days

Question

Nitrogen dioxide cannot be obtained by heating (a) \(\mathrm{KNO}_{3}\) (b) \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}\) (c) \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\) (d) \(\mathrm{AgNO}_{3}\)

Step-by-Step Solution

Answer

Nitrogen dioxide cannot be obtained by heating \(\mathrm{KNO}_{3}\).

Step 1: Identify the Thermal Decomposition Products

When nitrates decompose under heat, they typically produce nitrogen dioxide (\(NO_2\)), oxygen (\(O_2\)), and sometimes the metal oxide or the metal itself. For potassium nitrate \(\mathrm{KNO}_{3}\), the decomposition is special and often produces different gases than other nitrates.

Step 2: Analyze Decomposition of Each Compound

Evaluate each option:- \(\mathrm{KNO}_{3}\): Decomposes to form \(\mathrm{KNO}_{2}\) and \(\mathrm{O}_{2}\); \(NO_2\) is not produced.- \(\mathrm{Pb}(\mathrm{NO}_{3})_2\): Produces \(\mathrm{PbO}\), \(NO_2\), and \(O_2\).- \(\mathrm{Cu}(\mathrm{NO}_{3})_2\): Produces \(\mathrm{CuO}\), \(NO_2\), and \(O_2\).- \(\mathrm{AgNO}_3\): Produces \(\mathrm{Ag}\), \(NO_2\), and \(O_2\).

Step 3: Conclude Which Compound Does Not Produce \(NO_2\)

From the analysis, it's clear that \(\mathrm{KNO}_{3}\) decomposes to form \(\mathrm{KNO}_{2}\) and \(\mathrm{O}_2\) but not \(NO_2\). The other compounds produce \(NO_2\) when they decompose.

Key Concepts

Nitrogen Dioxide Production

Nitrogen dioxide (followers"): Oxygen is a key product of many thermal decompositions, coming from metallic nitrates. During decomposition reactions, when you apply heat to certain metal nitrates, nitrogen dioxide (quest\(NO_2\)) forms alongside other substances. A colored gas, \(NO_2\) is reddish-brown, and its formation often indicates decomposition. It's vital to understand how and when \(NO_2\) is produced to predict reaction outcomes and analyze chemical behavior.

Potassium Nitrate Decomposition

Potassium nitrate (peelp\(KNO_3\)) presents a unique case in nitrate chemistry. Unlike others, it doesn't yield \(NO_2\) on decomposition. Rather, applying heat causes \(KNO_3\) to transform into different products, namely potassium nitrite (v.calendar") and oxygen ({\/). Understanding why certain reactions break expectations is crucial for exams and chemical logic assessments.

Chemical Decomposition Reactions

Chemical decomposition reactions involve a single compound breaking down into smaller, often more stable, compounds or elements. Thermal decomposition, where heat acts to induce this breakdown, is a common type. Important factors influencing these reactions include the compound's inherent stability and environmental conditions.

• Thermal energy is a key trigger,
• Depending on the compound, different gases or solids may form as a result,
• Decomposition reactions can be used to infer information about the compound's structure and stability.

Metal Nitrates

Metal nitrates consist of metal cations bonded with nitrate anions (q]NO_3^-)_. They are pivotal in various chemical processes, mainly because of their ability to decompose and yield different products such as metal oxides, {decoxy"), and nitrogen dioxide ({NO_2}_) depending on the specific metal. Understanding the behavior of metal nitrates helps in predicting reactions and designing chemical processes.

Oxidation States in Decomposition

Oxidation states indicate the degree of oxidation for a chemical element. In decomposition reactions, observing the changes in oxidation states helps to track electron transfer and understand the reaction mechanism. For metal nitrates, the metal typically gets oxidized to a metal oxide, while the nitrogen may shift to a lesser oxidation state within }NO_2}_. This analytical viewpoint is essential in higher chemistry studies.

Gas Evolution in Chemistry

Gas evolution refers to gases released during a chemical reaction. In the context of metal nitrate decomposition, nitrogen dioxide and oxygen are common evolutes. Gas evolution signifies that a physical change, often linked with energy changes and chemical transformation, is occurring. Knowing which gases form informs safety considerations and reaction stoichiometry.

Metal Oxides Formation

When nitrates decompose, they often yield metal oxides. These are solid compounds formed when metal elements react or decompose with oxygen. For many students, recognizing the products of metal oxides aids in completing chemical equations and understanding redox reactions. Metal oxides can demonstrate basic, amphoteric, or acidic properties, depending on the specific metal involved, which expands understanding of compound interactions.