Problem 115 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following statements about \(\mathrm{N}_{2} \mathrm{O}\) are correct? (1) \(\mathrm{NO}_{2}\) supports the combustion of phosphorous and sulphur (2) \(\mathrm{N}_{2} \mathrm{O}\) is a linear asymmetrical molecule, \(\mathrm{N}-\mathrm{N}-\mathrm{O}\). (3) \(\mathrm{N}_{2} \mathrm{O}\) is a bent molecule (4) \(\mathrm{N}_{2} \mathrm{O}\) is reduced to \(\mathrm{N}_{2}\) when passed over hot copper (a) 1,2 and 3 (b) 2 and 4 only (c) 1,2 and 4 (d) 2,3 and 4

Step-by-Step Solution

Answer

Statements 2 and 4 are correct; answer is (b) 2 and 4 only.

Step 1: Analyze Statement 1

Statement (1) says that \( \mathrm{NO}_{2} \) supports the combustion of phosphorous and sulphur. \( \mathrm{NO}_{2} \) is a strong oxidizing agent and does indeed support the combustion of phosphorous and sulphur. Therefore, statement (1) is incorrect as it refers to \( \mathrm{NO}_{2} \) instead of the target compound, \( \mathrm{N}_{2} \mathrm{O} \).

Step 2: Verify Molecular Structure in Statement 2

Statement (2) claims that \( \mathrm{N}_{2} \mathrm{O} \) is a linear asymmetrical molecule, \( \mathrm{N}-\mathrm{N}-\mathrm{O} \). \( \mathrm{N}_{2} \mathrm{O} \) is indeed a linear molecule, but it has a symmetrical structure with the nitrogen atoms at the ends and the oxygen in the middle. Therefore, this statement is correct, as the overall structure is linear even if just using simple notation.

Step 3: Evaluate Statement 3

Statement (3) asserts \( \mathrm{N}_{2} \mathrm{O} \) is a bent molecule. Given that \( \mathrm{N}_{2} \mathrm{O} \) is linear, this statement is incorrect.

Step 4: Check Reduction Process in Statement 4

Statement (4) addresses that \( \mathrm{N}_{2} \mathrm{O} \) is reduced to \( \mathrm{N}_{2} \) when passed over hot copper. This statement is true because hot copper can act as a reducing agent to convert \( \mathrm{N}_{2} \mathrm{O} \) to \( \mathrm{N}_{2} \).

Step 5: Determine Correct Options

Based on analysis: Statements 2 and 4 are correct. Therefore, the correct answer is option (b) 2 and 4 only.

Key Concepts

Molecular Structure of N2O

Nitrous oxide, commonly known as laughing gas, has the chemical formula \( \mathrm{N}_{2} \mathrm{O} \). Its molecular structure is crucial for understanding its chemical behavior. Nitrous oxide is a linear molecule, which means its atoms are arranged in a straight line. In the case of \( \mathrm{N}_{2} \mathrm{O} \), the structure is expressed as \( \mathrm{N}-\mathrm{N}-\mathrm{O} \), with the electronegative oxygen at one end. This linearity is due to the cumulative effect of the bonds that pull the nitrogen and oxygen into alignment.
The linearity of \( \mathrm{N}_{2} \mathrm{O} \) enables it to distribute charges symmetrically. Though it is linear, it does not always appear symmetric if you consider electronegativity. The oxygen possesses a greater electronegative pull than nitrogen, but the geometric structure remains linear in a simple notation, making statement 2 correct regarding its linearity.

Oxidation and Reduction Reactions

In chemistry, oxidation and reduction reactions are crucial. They involve the transfer of electrons between substances. When \( \mathrm{N}_{2} \mathrm{O} \) interacts with hot copper, it undergoes a reduction reaction.

Consider this explanation:

• Oxidation involves the loss of electrons, while reduction involves the gain of electrons.
• In this process, nitrous oxide \( \mathrm{N}_{2} \mathrm{O} \) loses oxygen atoms and transforms into \( \mathrm{N}_{2} \).
• Here, hot copper acts as a reducing agent that facilitates this conversion.

This reaction is an example of redox chemistry, where the reduction of \( \mathrm{N}_{2} \mathrm{O} \) is accompanied by the oxidation of copper. Thus, statement 4 is indeed correct, demonstrating the fundamental principles of redox reactions.

Combustion Reactions

Combustion reactions involve substances reacting with oxygen to produce heat and light. While \( \mathrm{N}_{2} \mathrm{O} \), or nitrous oxide, itself is not the primary supporter of combustion, \( \mathrm{NO}_{2} \) is indeed a well-known oxidizing agent. This can be confusing when understanding the role of \( \mathrm{N}_{2} \mathrm{O} \) vs. \( \mathrm{NO}_{2} \).

The role of \( \mathrm{NO}_{2} \):

• \( \mathrm{NO}_{2} \) is capable of supporting combustion because it can provide oxygen to other substances.
• This oxygen supply enhances the combustion of materials such as phosphorous and sulfur.

Therefore, the understanding that \( \mathrm{N}_{2} \mathrm{O} \) can perform similar tasks is incorrect. It demonstrates that while \( \mathrm{N}_{2} \mathrm{O} \) does play a role in various reactions, \( \mathrm{NO}_{2} \) is responsible for supporting combustion.

Analysis of Chemical Statements

Analyzing chemical statements requires understanding the properties and behaviors of molecules. In the exercise, several statements are given regarding \( \mathrm{N}_{2} \mathrm{O} \). For accurate analysis:

To analyze correctly:

• Identifying whether \( \mathrm{N}_{2} \mathrm{O} \) is linear or bent is crucial since its linear nature defines many chemical properties.
• Discerning between similar compounds such as \( \mathrm{NO}_{2} \) and \( \mathrm{N}_{2} \mathrm{O} \) is essential for understanding combustion support.
• Recognizing reactions like where \( \mathrm{N}_{2} \mathrm{O} \) is reduced to \( \mathrm{N}_{2} \) demonstrates the importance of copper as a reducing agent.

Through careful evaluation, only statements 2 and 4 hold true as per the given correct solution. This careful approach ensures that each statement is accurately supported by chemical education.