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

Ammonium nitrite \(\text{NH}_4\text{NO}_2\) does not release \(\text{NH}_3\) upon heating.

Step 1: Identify Ammonium Compounds

We need to identify which ammonium compound is in question. The options given are ammonium sulfate \((\text{NH}_4)_2\text{SO}_4\), ammonium carbonate \((\text{NH}_4)_2\text{CO}_3\), ammonium nitrite \(\text{NH}_4\text{NO}_2\), and ammonium chloride \(\text{NH}_4\text{Cl}\).

Step 2: Predict Decomposition Products

When ammonium compounds are heated, they can decompose to release ammonia \(\text{NH}_3\). We need to determine the decomposition reaction for each compound: 1. \((\text{NH}_4)_2\text{SO}_4\) typically decomposes to produce ammonia.2. \((\text{NH}_4)_2\text{CO}_3\) also decomposes to release ammonia.3. \(\text{NH}_4\text{NO}_2\) decomposes into \(\text{N}_2\) and \(\text{H}_2\text{O}\), not \(\text{NH}_3\).4. \(\text{NH}_4\text{Cl}\) gives off ammonia upon heating.

Step 3: Determine Which Does Not Produce Ammonia

From the previous step, we observe that \(\text{NH}_4\text{NO}_2\) decomposes to form nitrogen gas and water, not ammonia. The other compounds, \((\text{NH}_4)_2\text{SO}_4\), \((\text{NH}_4)_2\text{CO}_3\), and \(\text{NH}_4\text{Cl}\), do release ammonia when heated.

Key Concepts

Decomposition Reactions

A decomposition reaction is a type of chemical reaction where a single compound breaks down into two or more simpler substances. These reactions are often characterized by the general formula \( AB \rightarrow A + B \). In the context of ammonium compounds, decompositions often occur with the application of heat, which encourages the breakdown of the compound. When dealing with ammonium compounds, decomposition reactions typically produce gases such as ammonia \( \text{NH}_3 \) or nitrogen \( \text{N}_2 \), along with other byproducts like water \( \text{H}_2\text{O} \). Understanding these decomposition reactions is crucial because it helps predict which gases are released when a compound is heated. For students, being able to identify how a compound will decompose allows them to predict the products formed, making this a vital skill in chemistry.

Thermal Decomposition

Thermal decomposition is a specific type of decomposition reaction that occurs when heat is applied to a chemical substance. The applied heat provides the energy necessary to break the chemical bonds within a molecule. This process leads to the breakup of the original substance into simpler chemicals. Some important aspects of thermal decomposition include:

• Different compounds have different decomposition temperatures, meaning they require different amounts of heat to decompose.
• For ammonium compounds, the common products of thermal decomposition are gases such as ammonia, nitrogen, and water vapor.
• Understanding the products of thermal decomposition is crucial in industries that involve heating compounds, as the release of certain gases can impact both safety and product yield.

Hence, knowing which ammonium compounds decompose into which gases can have practical applications, such as preventing unwanted reactions or safely managing gas emissions.

Gas Evolution

Gas evolution is an important concept in both chemistry and environmental science. It refers to the release of a gas from a reaction mixture. This often occurs during decomposition reactions when a compound breaks down and releases one or more gases. For ammonium compounds:

• Ammonium sulfate and carbonate commonly release ammonia gas when heated.
• Ammonium nitrite, on the other hand, produces nitrogen gas \( \text{N}_2 \) instead of ammonia \( \text{NH}_3 \).
• The identification of the evolved gas can help diagnose which decomposition reaction has occurred.

Gas evolution is especially relevant in laboratory experiments and industrial processes. It is essential to anticipate gas evolution to ensure proper containment and control of gases which may be hazardous or undesirable. Furthermore, by monitoring gas evolution, chemists can optimize reactions to ensure maximum efficiency and yield of desired products.