Problem 7 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

On heating compound (A) gives a gas (B) which is a constituent of air. This gas when treated with \(\mathrm{H}_{2}\) in the presence of a catalyst gives another gas (C) which is basic in nature. (A) should not be : [Main Sep. 02, 2020 (I)] (a) \(\mathrm{NaN}_{3}\) (b) \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}\) (c) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) (d) \(\mathrm{NH}_{4} \mathrm{NO}_{2}\)

Step-by-Step Solution

Answer

(b) \(\mathrm{Pb}\left(\mathrm{NO}_3\right)_2\) should not be compound (A).

Step 1: Understand the Problem

We need to find out which compound (A) does not decompose into a gas (B) that is a constituent of air and can produce another basic gas (C) when treated with hydrogen and a catalyst.

Step 2: Analyze Option (a): \(\mathrm{NaN}_3\)

\(\mathrm{NaN}_3\) decomposes to produce \(\mathrm{N}_2\), which is a constituent of air. \(\mathrm{N}_2\) can react with hydrogen in the presence of a catalyst to form \(\mathrm{NH}_3\), which is a basic gas. This matches the description in the problem, so \(\mathrm{NaN}_3\) could be compound (A).

Step 3: Analyze Option (b): \(\mathrm{Pb}\left(\mathrm{NO}_3\right)_2\)

\(\mathrm{Pb}\left(\mathrm{NO}_3\right)_2\) decomposes to produce \(\mathrm{NO}_2\) and \(\mathrm{O}_2\). \(\mathrm{O}_2\) is a component of air, but it cannot react with hydrogen to produce a basic gas. Thus, \(\mathrm{Pb}\left(\mathrm{NO}_3\right)_2\) should not be compound (A).

Step 4: Analyze Option (c): \(\left(\mathrm{NH}_4\right)_2 \mathrm{Cr}_2\mathrm{O}_7\)

\(\left(\mathrm{NH}_4\right)_2 \mathrm{Cr}_2\mathrm{O}_7\) decomposes to produce \(\mathrm{N}_2\), a constituent of air. \(\mathrm{N}_2\) can react with hydrogen to form \(\mathrm{NH}_3\), a basic gas. This fits the conditions, so \(\left(\mathrm{NH}_4\right)_2 \mathrm{Cr}_2\mathrm{O}_7\) could be compound (A).

Step 5: Analyze Option (d): \(\mathrm{NH}_4 \mathrm{NO}_2\)

\(\mathrm{NH}_4 \mathrm{NO}_2\) decomposes to produce \(\mathrm{N}_2\), which is a constituent of air. \(\mathrm{N}_2\) can react with hydrogen to produce \(\mathrm{NH}_3\), a basic gas. Hence, \(\mathrm{NH}_4 \mathrm{NO}_2\) could be compound (A).

Step 6: Conclude the Analysis

Since \(\mathrm{Pb}\left(\mathrm{NO}_3\right)_2\) is the only option that does not produce a gas that can react with hydrogen to form a basic gas, it should not be compound (A).

Key Concepts

Gas Reactions

Gas reactions are a fundamental part of inorganic chemistry and involve the transformation of gaseous substances through chemical reactions. One popular scenario involves a certain compound decomposing into a gas. This type of reaction is known as thermal decomposition, as it occurs upon heating. For example, in the exercise above, sodium azide (\(\mathrm{NaN}_3\)) decomposes to produce nitrogen gas (\(\mathrm{N}_2\)). Nitrogen is a common gas in our atmosphere, making up approximately 78% of the air we breathe.

When these gases are produced, they may either remain stable or participate in further reactions. The exercise describes a reaction where nitrogen gas, \(\mathrm{N}_2\), reacts with hydrogen (\(\mathrm{H}_2\)) in the presence of a catalyst to form ammonia (\(\mathrm{NH}_3\)), a process crucial in producing fertilizers. Such reactions are often conducted under specific conditions to facilitate the reaction, like elevated temperatures and pressures.

• Gas reactions like these can be influenced by factors such as temperature and pressure.
• The catalysts used help in lowering the activation energy of the reactions, making them more feasible under controlled conditions.

Nitrogen Compounds

Nitrogen compounds are a diverse group of materials that contain nitrogen. They play vital roles in many areas of chemistry and industry. **In the example problem, we are dealing with several nitrogenous compounds that decompose to release nitrogen gas:**

• Sodium azide (\(\mathrm{NaN}_3\)).
• Ammonium dichromate (\((\mathrm{NH}_4)_2 \mathrm{Cr}_2 \mathrm{O}_7\)).
• Ammonium nitrite (\(\mathrm{NH}_4 \mathrm{NO}_2\)).

Ammonium nitrite and ammonium dichromate are well-known for their ability to release \(\mathrm{N}_2\) upon heating. When these compounds decompose, they undergo chemical changes that result in the removal of oxygen atoms and the production of nitrogen.

Nitrogen itself is quite inert due to its triple bond (\(\mathrm{N}\equiv\mathrm{N}\)), but in the presence of a catalyst, it becomes reactive enough to form ammonia once combined with hydrogen. Understanding the behavior of these nitrogen compounds is crucial in facilitating reactions that are beneficial in industrial applications like fertilizer production.

Basic Gases

Basic gases are part of a larger category of gases that have the ability to accept proton(s) or donate electron pairs. One classic example of a basic gas is ammonia (\(\mathrm{NH}_3\)). This gas is known for its ability to act as a base due to its lone pair of electrons on the nitrogen atom, which can easily accept a proton.

Ammonia is paramount in many chemical processes. It is produced industrially via the Haber process, involving nitrogen and hydrogen gases reacting in the presence of an iron catalyst. This basic gas plays a critical role in agricultural and industrial applications, such as:

• Ammonia is extensively used in the production of fertilizers, specifically ammonium nitrate.
• It’s also employed as a refrigerant due to its efficient heat absorption properties.

Ammonia’s characteristic pungent smell is a reminder of its presence and provides a signal for its application as a basic gas in various chemical reactions. Understanding how these gases behave helps in their safe and effective application in different domains.