Problem 71 - A Complete Resource Book in Chemistry for JEE Main

Question

\(\mathrm{NH}_{3}\) cannot be obtained by (a) heating of \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) or \(\mathrm{NH}_{4} \mathrm{NO}_{2}\) (b) heating of \(\mathrm{NH}_{4} \mathrm{Cl}\) or \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{CO}_{3}\) (c) heating of \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) with \(\mathrm{NaOH}\) (d) reaction of AIN or \(\mathrm{Mg}_{3} \mathrm{~N}_{2}\) or \(\mathrm{CaCN}_{2}\) with \(\mathrm{H}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

\( \text{NH}_3 \) cannot be obtained by heating \( \text{NH}_4\text{NO}_3 \) or \( \text{NH}_4\text{NO}_2 \).

Step 1: Analyzing Option (a)

Let's break down reaction (a): When we heat \( \text{NH}_4\text{NO}_3 \), it decomposes to form nitrous oxide \( \text{N}_2\text{O} \) and water, not ammonia. When we heat \( \text{NH}_4\text{NO}_2 \), it decomposes into nitrogen gas \( \text{N}_2 \) and water. Therefore, \( \text{NH}_3 \) cannot be obtained from this process.

Step 2: Analyzing Option (b)

Option (b) involves heating \( \text{NH}_4\text{Cl} \) and \( (\text{NH}_4)_2\text{CO}_3 \). Both compounds release \( \text{NH}_3 \) upon heating; \( \text{NH}_4\text{Cl} \) forms \( \text{NH}_3 \) and \( \text{HCl} \), while \( (\text{NH}_4)_2\text{CO}_3 \) forms \( \text{NH}_3 \), \( \text{CO}_2 \), and water.

Step 3: Analyzing Option (c)

When \( \text{NH}_4\text{NO}_3 \) is treated with \( \text{NaOH} \), ammonia gas \( \text{NH}_3 \) is produced along with water and sodium nitrate \( \text{NaNO}_3 \). Hence, \( \text{NH}_3 \) can be obtained through this reaction.

Step 4: Analyzing Option (d)

The compounds \( \text{AlN} \), \( \text{Mg}_3\text{N}_2 \), and \( \text{CaCN}_2 \) react with water to produce \( \text{NH}_3 \). For example, \( \text{AlN} \) plus water yields \( \text{NH}_3 \) and \( \text{Al(OH)}_3 \); therefore \( \text{NH}_3 \) can be obtained here.

Step 5: Conclusion

Based on the analysis of the reactions, option (a) is the correct answer because \( \text{NH}_3 \) cannot be obtained by heating \( \text{NH}_4\text{NO}_3 \) or \( \text{NH}_4\text{NO}_2 \).

Key Concepts

Decomposition Reactions

Decomposition reactions involve breaking down a single compound into two or more simpler substances. These reactions often require heat energy to break the chemical bonds, and they play an essential role in chemistry by offering a method to produce certain gases or reactants.
\[ \text{General form: } AB \rightarrow A + B \]
In the context of ammonia preparation, certain ammonium compounds, such as ammonium nitrate \((\text{NH}_4\text{NO}_3)\) and ammonium nitrite \((\text{NH}_4\text{NO}_2)\), undergo decomposition when heated. However, they decompose to form gases like nitric oxide \((\text{N}_2\text{O})\) and nitrogen \((\text{N}_2)\), respectively, rather than producing ammonia \((\text{NH}_3)\).
Understanding decomposition reactions helps us predict the products formed from heating compounds, which is crucial for processes like gas manufacturing and industrial chemistry.

Ammonium Compounds

Ammonium compounds are chemical substances that contain the ammonium ion \((\text{NH}_4^+)\). They are versatile and widely used in both industrial and laboratory settings. When heated, many of these compounds decompose to release ammonia gas \((\text{NH}_3)\).
For example:

• Heating \(\text{NH}_4\text{Cl}\) produces \(\text{NH}_3\) and hydrochloric acid \((\text{HCl})\).
• Heating \((\text{NH}_4)_2\text{CO}_3\) results in \(\text{NH}_3\), carbon dioxide \((\text{CO}_2)\), and water.
  

These reactions are significant for ammonia preparation, especially in scenarios where a simple and direct method for gas collection is required. Comprehending the behavior of these ammonium compounds in various conditions allows chemists to tailor the production of ammonia efficiently.

Chemical Reactions Analysis

Analyzing chemical reactions involves understanding the reactants, products, and the conditions under which the reactions occur. This analysis is vital to predict the possible outcomes of chemical processes.
In the case of ammonia gas production, a detailed examination of how compounds react—such as ammonium compounds reacting with bases like \(\text{NaOH}\) or with water—allows chemists to choose the appropriate method for synthesizing \(\text{NH}_3\).
By analyzing:

• \(\text{NH}_4\text{NO}_3\) reacting with \(\text{NaOH}\) to form ammonia, water, and sodium nitrate \((\text{NaNO}_3)\)
• \(\text{Mg}_3\text{N}_2\) or \(\text{CaCN}_2\) reacting with water to yield \(\text{NH}_3\)

Chemists can efficiently manipulate these reactions to achieve the desired chemical transformation. Understanding these interactions provides clarity on the conditions required for effective ammonia preparation and the types of compounds that serve as suitable precursors.