Problem 119 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following compounds give nitrogen on heating ? (a) \(\mathrm{NaN}_{3}\) (b) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) (c) \(\mathrm{NH}_{4} \mathrm{NO}_{2}\) (d) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\)

Step-by-Step Solution

Answer

Compounds (a), (c), and (d) give nitrogen on heating.

Step 1: Analyze Sodium Azide (\(\mathrm{NaN}_3\))

Upon heating, sodium azide undergoes decomposition to form sodium metal and nitrogen gas. The reaction is \(2\mathrm{NaN}_3 \rightarrow 2\mathrm{Na} + 3\mathrm{N}_2\). Hence, \(\mathrm{NaN}_3\) produces nitrogen gas on heating.

Step 2: Check Ammonium Sulfate (\(\left(\mathrm{NH}_4\right)_2 \mathrm{SO}_4\))

When ammonium sulfate is heated, it decomposes into ammonia gas and sulfur dioxide, but it does not directly produce nitrogen gas. Therefore, \(\left(\mathrm{NH}_4\right)_2 \mathrm{SO}_4\) does not yield nitrogen on heating.

Step 3: Evaluate Ammonium Nitrite (\(\mathrm{NH}_4 \mathrm{NO}_2\))

Ammonium nitrite decomposes upon heating to form water and nitrogen gas, following the reaction \(\mathrm{NH}_4\mathrm{NO}_2 \rightarrow 2\mathrm{H}_2\mathrm{O} + \mathrm{N}_2\). Thus, \(\mathrm{NH}_4 \mathrm{NO}_2\) produces nitrogen on heating.

Step 4: Assess Ammonium Dichromate (\(\left(\mathrm{NH}_4\right)_2 \mathrm{Cr}_2 \mathrm{O}_7\))

When heated, ammonium dichromate decomposes to produce chromium(III) oxide, nitrogen gas, and water. The reaction can be written as \(\left(\mathrm{NH}_4\right)_2 \mathrm{Cr}_2 \mathrm{O}_7 \rightarrow \mathrm{Cr}_2 \mathrm{O}_3 + \mathrm{N}_2 + 4\mathrm{H}_2\mathrm{O}\). Therefore, it produces nitrogen gas on heating.

Key Concepts

Sodium Azide decomposition

Sodium azide ( \(\mathrm{NaN}_3\)) is an interesting compound that produces nitrogen gas when heated. This process is known as decomposition, where one compound breaks down into simpler substances. For sodium azide, the decomposition reaction is as follows:

• \(2\mathrm{NaN}_3\rightarrow 2\mathrm{Na} + 3\mathrm{N}_2\)

When sodium azide is heated, it breaks down to form sodium metal and nitrogen gas. This reaction is significant because nitrogen gas is released in its diatomic form \(\mathrm{N}_2\).
This is the same form of nitrogen found in the atmosphere. Sodium azide is often used in car airbags for this reason, as it can produce a large amount of nitrogen gas quickly, inflating the airbag rapidly during a collision.
It's a great example of a compound that decomposes to release a useful byproduct in everyday technology.

Ammonium Sulfate decomposition

Ammonium sulfate \(\left(\mathrm{NH}_4\right)_2\mathrm{SO}_4\) is a different story when it comes to nitrogen gas production. Upon heating, ammonium sulfate undergoes decomposition. However, it does not release nitrogen gas in the process. Instead, it breaks down to form:

• Ammonia gas \(\mathrm{NH}_3\)
• Sulfur dioxide \(\mathrm{SO}_2\)

This lack of nitrogen gas production makes ammonium sulfate different from its counterparts like sodium azide. While ammonium sulfate is a valuable fertilizer, known for providing essential nutrients to plants, it does not contribute to nitrogen gas emissions when heated.
Rather, its decomposition products can have different roles and effects, such as replenishing soil nutrients or undergoing further reactions in industrial processes.

Ammonium Nitrite reaction

When it comes to ammonium nitrite \(\mathrm{NH}_4\mathrm{NO}_2\), this compound is notable for its ability to release nitrogen gas when heated. The decomposition reaction is straightforward and occurs as follows:

• \(\mathrm{NH}_4\mathrm{NO}_2\rightarrow 2\mathrm{H}_2\mathrm{O} + \mathrm{N}_2\)

In this reaction, ammonium nitrite decomposes to produce water and nitrogen gas. This reaction is important and often used to produce nitrogen gas in laboratory settings due to its simplicity and effectiveness.
The process showcases a classic example of a thermal decomposition reaction, where a single compound breaks down to form two different products.
This process demonstrates how easily nitrogen can be obtained by heating appropriate nitrogenous compounds.

Ammonium Dichromate decomposition

The decomposition of ammonium dichromate \(\left(\mathrm{NH}_4\right)_2\mathrm{Cr}_2\mathrm{O}_7\) is both colorful and visually striking, which makes it particularly interesting. Upon heating, this compound decomposes and produces:

• Chromium(III) oxide \(\mathrm{Cr}_2\mathrm{O}_3\)
• Nitrogen gas \(\mathrm{N}_2\)
• Water \(4\mathrm{H}_2\mathrm{O}\)

The reaction can be written as follows:\(\left(\mathrm{NH}_4\right)_2\mathrm{Cr}_2\mathrm{O}_7\rightarrow \mathrm{Cr}_2\mathrm{O}_3 + \mathrm{N}_2 + 4\mathrm{H}_2\mathrm{O}\)
This reaction is not only a source of nitrogen gas but also serves as a demonstration in chemistry classes due to the impressive orange-to-green color change of the chromium compounds.
Ammonium dichromate's decomposition highlights the fascinating interaction between thermal energy and chemical compounds, resulting in the generation of gases and vivid transformations.