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

Question

. The reddish brown coloured gas formed when nitric oxide is oxidised by air is [1979] (a) \(\mathrm{N}_{2} \mathrm{O}_{5}\) (b) \(\mathrm{N}_{2} \mathrm{O}_{4}\) (c) \(\mathrm{NO}_{2}\) (d) \(\mathrm{N}_{2} \mathrm{O}_{3}\)

Step-by-Step Solution

Answer

The reddish-brown gas is \(\mathrm{NO}_{2}\), so the answer is (c).

Step 1: Recognize the Chemical Reaction

When nitric oxide (NO) reacts with oxygen in the air, it forms nitrogen dioxide (NO_{2}). The balanced equation for its oxidation is: \[ 2 NO + O_2 \rightarrow 2 NO_2 \]This indicates that nitric oxide is oxidized to nitrogen dioxide when exposed to air.

Step 2: Identify the Properties of the Product

Nitrogen dioxide (\(\mathrm{NO}_{2}\)) is known for its characteristic reddish-brown color. Therefore, the gas formed as a result of this reaction is reddish-brown in color.

Step 3: Select the Correct Answer

Based on the given options and the properties of the products formed, the reddish-brown colored gas that forms when \(\mathrm{NO}\) is oxidized in air is nitrogen dioxide (\(\mathrm{NO}_{2}\)). Thus, the correct answer is option (c) \(\mathrm{NO}_{2}\).

Key Concepts

Chemical Reaction

A chemical reaction occurs when two or more substances interact to form new substances. In the case of nitric oxide (NO) reacting with oxygen (O_2) in the air, a chemical transformation occurs. During this process, the molecules of NO and O_2 collide and rearrange to form a new compound — nitrogen dioxide (NO_2).
The balanced chemical equation representing this reaction is:

• \(2 \text{ NO} + \text{O}_2 \rightarrow 2 \text{ NO}_2\)

This equation shows the conversion of two molecules of nitric oxide with one molecule of oxygen, resulting in two molecules of nitrogen dioxide. Balancing chemical equations is crucial as it reflects the conservation of mass principle, ensuring the same number of atoms on both sides of the equation.
Understanding the basic reactions like the oxidation of nitric oxide can help students grasp broader concepts in chemistry, such as reactivity and the formation of different chemical products.

Nitrogen Dioxide

Nitrogen dioxide ( NO_2 ) is a notable compound due to its distinct properties. One of its most noticeable features is its reddish-brown color. This color makes it easy to identify in various chemical reactions, such as when nitric oxide oxidizes in the air.

• Its molecular formula is NO_2 .
• It is a major air pollutant, often associated with environmental and health issues.

As a reactive nitrogen species, NO_2 is part of a group of gases called nitrogen oxides, or NO _x . These gases are significant in atmospheric chemistry due to their role in forming smog and acid rain.
Understanding the properties and implications of nitrogen dioxide is essential not only for solving textbook problems but also for comprehending its role in our environment.

Gas Properties

Gases have unique properties that distinguish them from liquids and solids, some of which play a critical role in chemical reactions and solutions. Understanding these properties can aid in comprehending how reactions like the oxidation of nitric oxide to nitrogen dioxide occur.

Key properties of gases include:

• Diffusion: Gases mix completely with other gases, as demonstrated by the mixing of nitric oxide with oxygen.
• Pressure: Gases exert pressure on their containers, which can affect reaction rates.
• Color: The color of a gas, such as the reddish-brown hue of nitrogen dioxide, can indicate the presence of certain compounds.
• Reactivity: Gases may react differently compared to their liquid or solid forms, as seen in the oxidation of nitric oxide.

By understanding gas properties, students can better predict the behavior of gases in chemical reactions, which is vital for many scientific and industrial processes.