Problem 24 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Extra pure \(\mathrm{N}_{2}\) can be obtained by heating (a) \(\mathrm{NH}_{3}\) with \(\mathrm{CuO}\) (b) \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) (c) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) (d) \(\mathrm{Ba}\left(\mathrm{N}_{3}\right)_{2}\)

Step-by-Step Solution

Answer

Option (c) and (d) provide extra pure nitrogen gas.

Step 1: Identify Reactions

We need to identify which chemical reactions produce pure nitrogen gas. The reactions for each option are known from chemical literature.

Step 2: Evaluate Option (a)

The reaction between ammonia (H_{3}) and copper(II) oxide ( ext{CuO}) is: \[ 2 ext{NH}_{3} + 3 ext{CuO} ightarrow 3 ext{Cu} + 3 ext{H}_{2} ext{O} + ext{N}_{2} \] This reaction produces nitrogen gas along with water and copper. However, it's not known for producing extra pure nitrogen sample due to the presence of other byproducts.

Step 3: Evaluate Option (b)

Ammonium nitrate ( ext{NH}_{4} ext{NO}_{3}) decomposes upon heating: \[ ext{NH}_{4} ext{NO}_{3} ightarrow 2 ext{H}_{2} ext{O} + ext{N}_{2} ext{O} \] This reaction produces water vapor and nitrous oxide ( ext{N}_{2} ext{O}), not nitrogen gas.

Step 4: Evaluate Option (c)

Upon heating ammonium dichromate (( ext{NH}_{4})_{2} ext{Cr}_{2} ext{O}_{7}), it decomposes: \[ ( ext{NH}_{4})_{2} ext{Cr}_{2} ext{O}_{7} ightarrow ext{Cr}_{2} ext{O}_{3} + 4 ext{H}_{2} ext{O} + ext{N}_{2} \] This reaction produces nitrogen gas along with chromium(III) oxide and water, leading to a possibly very pure form of nitrogen as solid byproduct is easily separated.

Step 5: Evaluate Option (d)

When barium azide ( ext{Ba}( ext{N}_{3})_{2}) is heated, it decomposes: \[ ext{Ba}( ext{N}_{3})_{2} ightarrow ext{Ba} + 3 ext{N}_{2} \] This reaction produces nitrogen gas and metallic barium, and it is known to yield extra pure nitrogen gas remaining gaseous ( ext{N}_{2}), much like option (c).

Key Concepts

Decomposition Reactions

Decomposition reactions are fundamental processes in chemistry where a single compound breaks down into simpler substances. They occur when heat, light, or electricity breaks the bonds within a chemical compound. This type of reaction is a crucial concept because it helps us understand how complex substances can be converted into simpler forms.
One typical example is the decomposition of ammonium dichromate, which breaks down when heated to produce nitrogen gas, chromium(III) oxide, and water.

• Ammonium dichromate ( (NH_{4})_{2}Cr_{2}O_{7} ): Produces (N_{2}) , (Cr_{2}O_{3}) , and water.
• Barium azide ( Ba(N_{3})_{2} ): Produces (Ba) and pure nitrogen ( 3N_{2} ).

Decomposition reactions are also essential for producing pure substances, especially gases like nitrogen, by ensuring that unwanted byproducts are minimized or easily separated.

Chemical Reactions of Ammonium Compounds

Ammonium compounds are fascinating as they readily undergo several chemical reactions, producing various substances. These reactions are central to many industrial and laboratory processes.
Ammonium nitrate ( NH_{4}NO_{3} ) is a well-known compound whose decomposition upon heating doesn't produce nitrogen gas but instead forms nitrous oxide ( N_{2}O ), a different nitrogen compound. Although not ideal for producing pure nitrogen, these reactions still hold value for other applications.
On the other hand, heating ammonium dichromate ( (NH_{4})_{2}Cr_{2}O_{7} ) results in the formation of nitrogen gas directly, making it a preferred choice for obtaining nitrogen( N_{2} ) due to the easy separation from solid byproducts.

• Ammonium nitrate ( NH_{4}NO_{3} ): Produces water and nitrous oxide, not practical for pure nitrogen extraction.
• Ammonium dichromate ( (NH_{4})_{2}Cr_{2}O_{7} ): Decomposition provides nitrogen gas suitable for use.

Understanding how ammonium compounds react is fundamental in selecting the appropriate starting materials for desired chemical processes.

Purity of Gases in Chemical Processes

The purity of gases produced in chemical processes is a vital consideration, especially for applications requiring high-quality reagents. In chemical reactions, the presence of impurities can lead to inefficiencies or undesirable side reactions.
When it comes to nitrogen gas production, the methods of obtaining this gas can vary significantly in the purity of the end product. For example, heating barium azide ( Ba(N_{3})_{2} ) leads to the production of nitrogen gas with impressive purity. This is because the metallic byproduct, barium, is solid and can be easily separated, leaving behind the gaseous nitrogen.

• Barium azide ( Ba(N_{3})_{2} ): Produces very pure nitrogen, easy to isolate due to solid byproduct.
• Ammonium dichromate ( (NH_{4})_{2}Cr_{2}O_{7} ): Also yields pure nitrogen gas by decomposing into gaseous and solid phases.

Maintaining the purity of gases is critical for processes that demand high precision and quality in the final products. It's important to select methods that ensure minimal contamination during the reaction.