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

The correct answer is option (a): heating of \( \mathrm{NH}_{4} \mathrm{NO}_{3} \) or \( \mathrm{NH}_{4} \mathrm{NO}_{2} \) cannot produce \( \mathrm{NH}_3 \).

Step 1: Analyzing Option (a)

The substances \( \mathrm{NH}_4\mathrm{NO}_3 \) and \( \mathrm{NH}_4\mathrm{NO}_2 \) decompose on heating. \( \mathrm{NH}_4\mathrm{NO}_3 \) decomposes to give nitrous oxide (\( \mathrm{N}_2\mathrm{O} \)) and water, not ammonia. \( \mathrm{NH}_4\mathrm{NO}_2 \), when heated, gives nitrogen gas and water, also no ammonia is formed.

Step 2: Analyzing Option (b)

Heating \( \mathrm{NH}_4\mathrm{Cl} \) releases ammonia gas and hydrogen chloride gas. Similarly, heating \( (\mathrm{NH}_4)_2\mathrm{CO}_3 \) releases ammonia gas, carbon dioxide, and water vapor.

Step 3: Analyzing Option (c)

When \( \mathrm{NH}_4\mathrm{NO}_3 \) is heated with \( \mathrm{NaOH} \), ammonia gas is liberated. This reaction involves the conversion of \( \mathrm{NH}_4^+ \) ions into ammonia under alkaline conditions.

Step 4: Analyzing Option (d)

Reaction of \( \mathrm{AlN}, \mathrm{Mg}_3\mathrm{N}_2, \text{ or } \mathrm{CaCN}_2 \) with water produces ammonia. For example, \( \mathrm{AlN} + 3\mathrm{H}_2\mathrm{O} \rightarrow \mathrm{Al(OH)}_3 + \mathrm{NH}_3 \). Similar reactions occur with other compounds mentioned.

Step 5: Conclusion

Based on the analysis above, ammonia \( \mathrm{NH}_3 \) is not produced by heating \( \mathrm{NH}_4\mathrm{NO}_3 \) or \( \mathrm{NH}_4\mathrm{NO}_2 \) alone. Therefore, option (a) is correct.

Key Concepts

Thermal Decomposition

Thermal decomposition is a chemical process where a compound breaks down into two or more substances when heated. This process doesn't always produce the same products, as it depends on the initial compound's composition. In the case of ammonium nitrate \( \mathrm{NH}_4\mathrm{NO}_3 \) and ammonium nitrite \( \mathrm{NH}_4\mathrm{NO}_2 \), heating leads to their decomposition.

• \( \mathrm{NH}_4\mathrm{NO}_3 \) decomposes into nitrous oxide \( \mathrm{N}_2\mathrm{O} \) and water.
• \( \mathrm{NH}_4\mathrm{NO}_2 \) decomposes to produce nitrogen gas and water.

You might expect ammonia \( \mathrm{NH}_3 \) to be produced because it contains nitrogen and hydrogen, but instead, these reactions eliminate ammonia entirely from the product list. Understanding these specific outputs through decomposition helps predict ammonia production viability in processes involving nitrogen compounds.

Ammonia Production

Ammonia production involves a variety of methods, where different reactions can yield \( \mathrm{NH}_3 \). Typically, ammonia can be liberated from compounds containing ammonium, a nitrogen-rich ion. However, not all processes produce ammonia efficiently.

• Heating \( \mathrm{NH}_4\mathrm{Cl} \) results in the liberation of ammonia gas alongside hydrogen chloride gas, making it a straightforward process.
• Similarly, heating \( (\mathrm{NH}_4)_2\mathrm{CO}_3 \) decomposes it into ammonia gas, carbon dioxide, and water vapor, thus also yielding \( \mathrm{NH}_3 \) effectively.

One common industrial method utilizes alkaline conditions, such as heating \( \mathrm{NH}_4\mathrm{NO}_3 \) with \( \mathrm{NaOH} \), to produce ammonia gas. Recognizing the efficacy of these processes is crucial for industrial applications and laboratory settings where ammonia is needed.

Reaction Analysis

Analyzing chemical reactions is essential in understanding decomposition and synthesis processes. Each reactant's transformation tells us which products will be formed and their quantities.

• Options like heating \( \mathrm{NH}_4\mathrm{Cl} \) or using \( \mathrm{NaOH} \) with ammonium compounds clearly demonstrate situations where ammonia is the definitive product.
• On the other hand, compounds like \( \mathrm{NH}_4\mathrm{NO}_3 \) and \( \mathrm{NH}_4\mathrm{NO}_2 \) show no ammonia formation, due to their specific decomposition pathways that favor nitrogen gases instead.
• Reactions involving compounds such as \( \mathrm{AlN} \) with water involve conversion to \( \mathrm{NH}_3 \), demonstrating how water-induced reactions can be suitable for ammonia synthesis.

By methodically analyzing each reaction, chemists can accurately predict chemical behavior and adjust conditions for desired outcomes.

Nitrogen Compounds

Nitrogen compounds are a diverse group, pivotal in various chemical reactions and industrial processes. They function as both reactants and products, displaying significant versatility. Compounds like ammonium nitrate and ammonium chloride contain the ammonium ion \( \mathrm{NH}_4^+ \), which can be manipulated under the right conditions to produce different gases or solids.

• The versatility of nitrogen compounds makes them essential in fertilizer production, where ammonium is a key nitrogen source.
• Through reactions, nitrogen compounds can produce ammonia, useful in agriculture and as a building block for other chemicals.
• Industrial processes often exploit the properties of nitrogen compounds to manufacture substances like explosives and refrigerants.

Understanding nitrogen compounds' chemical behaviors allows for their effective use and manipulation in both simple reactions and complex industrial processes.