Problem 10 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The correct order of the oxidation states of nitrogen in \(\mathrm{NO}, \mathrm{N}_{2} \mathrm{O}, \mathrm{NO}_{2}\) and \(\mathrm{N}_{2} \mathrm{O}_{3}\) is: [Main April 9, 2019 (I)] (a) \(\mathrm{NO}_{2}<\mathrm{NO}<\mathrm{N}_{2} \mathrm{O}_{3}<\mathrm{N}_{2} \mathrm{O}\) (b) \(\mathrm{NO}_{2}<\mathrm{N}_{2} \mathrm{O}_{3}<\mathrm{NO}<\mathrm{N}_{2} \mathrm{O}\) (c) \(\mathrm{N}_{2} \mathrm{O}<\mathrm{N}_{2} \mathrm{O}_{3}<\mathrm{NO}<\mathrm{NO}_{2}\) (d) \(\mathrm{N}_{2} \mathrm{O}<\mathrm{NO}<\mathrm{N}_{2} \mathrm{O}_{3}<\mathrm{NO}_{2}\)

Step-by-Step Solution

Answer

The correct order is (d): \(\mathrm{N}_2\mathrm{O}<\mathrm{NO}<\mathrm{N}_2\mathrm{O}_3<\mathrm{NO}_2\).

Step 1: Determine Oxidation State of NO

In NO, nitrogen is bonded to oxygen which has an oxidation number of -2. Let the oxidation number of nitrogen be \( x \). The sum of the oxidation numbers in a neutral molecule is 0: \( x + (-2) = 0 \). Solving for \( x \), we get \( x = +2 \). Thus, the oxidation state of nitrogen in NO is +2.

Step 2: Determine Oxidation State of N2O

In \(\mathrm{N}_2\mathrm{O}\), let the oxidation state of nitrogen be \( x \). Oxygen has an oxidation state of -2. The sum of oxidation states in the molecule is: \( 2x + (-2) = 0 \). Solving for \( x \), we find \( 2x = +2 \) which gives \( x = +1 \). Thus, the oxidation state of nitrogen in \(\mathrm{N}_2\mathrm{O}\) is +1.

Step 3: Determine Oxidation State of NO2

In \(\mathrm{NO}_2\), oxygen has a known oxidation state of -2. Thus, the total contribution of oxygen is \(2 \times (-2) = -4\). Let \( x \) be the oxidation state of nitrogen, then \( x + (-4) = 0 \). Solving for \( x \) gives \( x = +4 \). Therefore, the oxidation state of nitrogen in \(\mathrm{NO}_2\) is +4.

Step 4: Determine Oxidation State of N2O3

In \(\mathrm{N}_2\mathrm{O}_3\), set the oxidation state of nitrogen as \( x \). Oxygen has an oxidation state of -2, so total contribution from oxygen is \(3 \times (-2) = -6\). The equation is \( 2x + (-6) = 0 \). Solving for \( x \) gives \( 2x = +6 \), so \( x = +3 \). Thus, the oxidation state of nitrogen in \(\mathrm{N}_2\mathrm{O}_3\) is +3.

Step 5: Order the Oxidation States

We found the oxidation states as follows: \(\mathrm{N}_2\mathrm{O} = +1\), \(\mathrm{NO} = +2\), \(\mathrm{N}_2\mathrm{O}_3 = +3\), and \(\mathrm{NO}_2 = +4\). Ordering them from lowest to highest, we have \(\mathrm{N}_2\mathrm{O} < \mathrm{NO} < \mathrm{N}_2\mathrm{O}_3 < \mathrm{NO}_2\). Check the options and find this matches (d).

Key Concepts

Nitrogen Compounds

Nitrogen compounds are molecules that contain nitrogen atoms bonded to other elements. These are crucial in many chemical processes and play vital roles in nature and everyday life. Nitrogen has five valence electrons, allowing it to form a variety of compounds.
Here are some common types of nitrogen compounds:

• Nitric oxide (NO) - a free radical compound important in biology and as a signaling molecule.
• Nitrous oxide (N\(_2\)O) - also known as "laughing gas", used in anesthesia and as a propellant in whipped cream dispensers.
• Nitrogen dioxide (NO\(_2\)) - a reddish-brown toxic gas, a significant air pollutant.
• Nitrogen trioxide (N\(_2\)O\(_3\)) - an unstable compound often found in equilibrium with nitrogen dioxide and dinitrogen tetroxide.

Understanding how to calculate the oxidation state of nitrogen in these compounds helps in predicting their reactivity and their behavior in redox reactions.

Redox Reactions

Redox reactions are chemical reactions where the oxidation state of atoms changes due to the transfer of electrons. These reactions are essential to various processes, including metabolism, corrosion, and energy production in batteries.

Every redox reaction consists of two half-reactions:

• Oxidation - involves the loss of electrons, leading to an increase in oxidation state.
• Reduction - involves gaining electrons, resulting in a decrease in oxidation state.

To balance redox reactions, one must ensure that the electrons lost in oxidation are equal to those gained in reduction.
By understanding these principles, one can understand how compounds like nitrogen dioxide and nitric oxide participate in such transformations. Recognizing how nitrogen changes its oxidation state in these reactions helps in controlling pollution and understanding biological processes.

Chemical Bonding

Chemical bonding explains how atoms are held together in molecules and compounds. It accounts for the properties and behavior of substances.

Nitrogen compounds exhibit a variety of bonds:

• Covalent bonds - occur when atoms share pairs of electrons. For instance, in nitric oxide (NO), nitrogen forms a covalent bond with oxygen.
• Coordinate covalent bonds - occur when one atom donates both of the electrons that make up the bond. This is observed in complex nitrogen species.

The type of chemical bonding affects the stability, reactivity, and physical properties of compounds. For example, the stability of nitrogen oxide is critical in how it interacts with the environment, contributing either to atmospheric chemistry or human physiology.
Understanding chemical bonding is fundamental to predicting how nitrogen compounds behave in different conditions.