Problem 62 - A Complete Resource Book in Chemistry for JEE Main

Question

Ammonium compound which does not give \(\mathrm{NH}_{3}\) on heating is (a) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) (b) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{CO}_{3}\) (c) \(\mathrm{NH}_{4} \mathrm{NO}_{2}\) (d) \(\mathrm{NH}_{4} \mathrm{Cl}\)

Step-by-Step Solution

Answer

The compound is \(\mathrm{NH}_{4} \mathrm{NO}_{2}\).

Step 1: Understand the Problem

We need to identify which ammonium compound does not release ammonia (\(\mathrm{NH}_{3}\)) when heated. The options involve ammonium sulfate, ammonium carbonate, ammonium nitrite, and ammonium chloride.

Step 2: Analyze Each Option

We will analyze the thermal decomposition of each compound:- \((\mathrm{NH}_{4})_{2} \mathrm{SO}_{4}\): On heating, it decomposes to give ammonia, water, and sulfur dioxide.- \((\mathrm{NH}_{4})_{2} \mathrm{CO}_{3}\): Decomposes into ammonia, water, and carbon dioxide.- \(\mathrm{NH}_{4} \mathrm{NO}_{2}\): Decomposes into nitrogen gas and water.- \(\mathrm{NH}_{4} \mathrm{Cl}\): Sublimes partly to ammonia and hydrogen chloride.

Step 3: Identify Non-Ammonia Producing Compound

From the analysis, \(\mathrm{NH}_{4} \mathrm{NO}_{2}\) is the only compound that decomposes to give nitrogen and water without producing ammonia.

Step 4: Conclusion

Thus, the ammonium compound that does not release ammonia upon heating is \(\mathrm{NH}_{4} \mathrm{NO}_{2}\).

Key Concepts

Thermal Decomposition

Thermal decomposition is a chemical reaction where a compound breaks down into simpler substances when heated. This process involves adding heat, which provides the energy necessary to break chemical bonds within the compound. Such reactions are an essential part of chemistry, used in various applications such as metal extraction, and understanding them is crucial when studying chemical reactions.

In the context of ammonium compounds, thermal decomposition can lead to different outcomes based on the compound's composition. For example, ammonium sulfate \((\mathrm{NH}_{4})_{2}\mathrm{SO}_{4}\): decomposes to produce ammonia, sulfur dioxide, and water. Similarly, ammonium carbonate undergoes decomposition to release ammonia, carbon dioxide, and water.

• Ammonium sulfate: \((\mathrm{NH}_{4})_{2}\mathrm{SO}_{4} \to \mathrm{NH}_{3} + \mathrm{SO}_{2} + \mathrm{H}_{2} \mathrm{O}\)
• Ammonium carbonate: \((\mathrm{NH}_{4})_{2}\mathrm{CO}_{3} \to \mathrm{NH}_{3} + \mathrm{CO}_{2} + \mathrm{H}_{2} \mathrm{O}\)

Each decomposition reaction reveals a unique combination of gases and possibly other substances that a compound might release when heated.

Ammonium Nitrite

Ammonium nitrite, represented as \(\mathrm{NH}_{4} \mathrm{NO}_{2}\), is a unique ammonium compound because of how it behaves upon heating. Unlike other ammonium compounds that release ammonia, ammonium nitrite undergoes thermal decomposition to form nitrogen gas and water.

The reaction can be represented as:\[\mathrm{NH}_{4} \mathrm{NO}_{2} \to \mathrm{N}_{2} + 2\mathrm{H}_{2}\mathrm{O}\] This reaction occurs due to the instability of ammonium nitrite. Upon heating, ammonium nitrite breaks down into diatomic nitrogen (\(\mathrm{N}_{2}\)), which is an inert gas that makes up a significant portion of Earth's atmosphere. Water is also produced in the process.

• Key Point: This decomposition reaction is an example of a compound not producing ammonia, making ammonium nitrite distinct from other ammonium compounds.

Ammonia Production

Ammonia \((\mathrm{NH}_{3})\) is a compound composed of nitrogen and hydrogen, and it's commonly produced through the thermal decomposition of ammonium compounds. When decomposing ammonium sulfate or ammonium carbonate, ammonia is one of the significant products released.

Ammonia is an important chemical in various industries, primarily used in fertilizers to aid plant growth. It has other uses too, including household cleaning products and the manufacture of plastics, explosives, textiles, and dyes.

• Common Reactions:
• Ammonium sulfate \((\mathrm{NH}_{4})_{2}\mathrm{SO}_{4}\) decomposition releases ammonia.
• Ammonium chloride \((\mathrm{NH}_{4}\mathrm{Cl})\) also sublimates to give ammonia and hydrogen chloride.
Compared to ammonium nitrite, which does not yield ammonia upon heating, most other ammonium compounds are a source of ammonia production when they thermally decompose.