Problem 23 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

\text { (d) } \mathrm{NO}, \mathrm{HNO}_{3}, \mathrm{NH}_{4} \mathrm{Cl}, \mathrm{N}_{2}Which ordering of compounds is according to the decreasing order of the oxidation state of nitrogen? [2012] (a) \(\mathrm{HNO}_{3}, \mathrm{NO}, \mathrm{NH}_{4} \mathrm{Cl}, \mathrm{N}_{2}\) (b) \(\mathrm{HNO}_{3}, \mathrm{NO}, \mathrm{N}_{2}, \mathrm{NH}_{4} \mathrm{Cl}\) (c) \(\mathrm{HNO}_{3}, \mathrm{NH}_{4} \mathrm{Cl}, \mathrm{NO}, \mathrm{N}_{2}\)

Step-by-Step Solution

Answer

Option (b) is correct.

Step 1: Determine Oxidation States for Each Compound

First, we need to determine the oxidation state of nitrogen in each compound. 1. **In \( \mathrm{HNO}_{3} \)**: The oxidation state of nitrogen can be calculated as follows: We know hydrogen is +1, oxygen is -2. Let the oxidation state of nitrogen be \( x \). The equation becomes: \( 1 + x + 3(-2) = 0 \). Solving the equation gives \( x = +5 \).2. **In \( \mathrm{NO} \)**: Let the oxidation state of nitrogen be \( x \). The equation will be: \( x + (-2) = 0 \). Solving gives \( x = +2 \).3. **In \( \mathrm{NH}_{4} \mathrm{Cl} \)**: Here, nitrogen's oxidation state can be calculated by assuming \( x \) for nitrogen. In \( \mathrm{NH}_{4}^+ \), we have: \( 4(+1) + x = +1 \) leading to \( x = -3 \).4. **In \( \mathrm{N}_{2} \)**: Nitrogen in its diatomic form has an oxidation state of 0.

Step 2: Arrange Nitrogen Compounds by Decreasing Oxidation State

Now, order the compounds by the decreasing oxidation states of nitrogen:1. **\( \mathrm{HNO}_{3} \)**: +52. **\( \mathrm{NO} \)**: +23. **\( \mathrm{N}_{2} \)**: 04. **\( \mathrm{NH}_{4} \mathrm{Cl} \)**: -3

Step 3: Select the Correct Option

Now compare the order we've found: \( \mathrm{HNO}_{3} \), \( \mathrm{NO} \), \( \mathrm{N}_{2} \), \( \mathrm{NH}_{4} \mathrm{Cl} \) with the options given:(a)\( \mathrm{HNO}_{3}, \mathrm{NO}, \mathrm{NH}_{4} \mathrm{Cl}, \mathrm{N}_{2}\) (b) \( \mathrm{HNO}_{3}, \mathrm{NO}, \mathrm{N}_{2}, \mathrm{NH}_{4}\mathrm{Cl}\) (c) \( \mathrm{HNO}_{3}, \mathrm{NH}_{4} \mathrm{Cl}, \mathrm{NO}, \mathrm{N}_{2}\)The correct answer is (b) because it matches our calculated order: \( \mathrm{HNO}_{3}, \mathrm{NO}, \mathrm{N}_{2}, \mathrm{NH}_{4} \mathrm{Cl} \).

Key Concepts

Nitrogen Compounds

Nitrogen can form a wide variety of compounds due to its ability to exhibit different oxidation states. This allows nitrogen to participate in a range of chemical structures and interactions. These compounds include nitric acid \(\text{(HNO}_3)\), nitric oxide \(\text{(NO)}\), ammonium chloride \(\text{(NH}_4\text{Cl)}\), and molecular nitrogen \(\text{(N}_2)\).

• **Nitric acid (\(\text{HNO}_3\))** is a strong acid commonly used in the manufacture of fertilizers and explosives. In this compound, nitrogen exhibits its highest common oxidation state of +5.
• **Nitric oxide (\(\text{NO}\))** is a gas composed of one nitrogen atom and one oxygen atom. In this molecule, nitrogen has an oxidation state of +2 and it plays a critical role as a signaling molecule in biological processes.
• **Ammonium chloride (\(\text{NH}_4\text{Cl)}\)** is a salt consisting of ammonia and hydrogen chloride. In this compound, nitrogen holds an oxidation state of -3, which is common in ammonia-like structures.
• **Molecular nitrogen (\(\text{N}_2\))** is a diatomic gas that makes up a significant portion of Earth's atmosphere. It has an oxidation state of 0, due to the equal sharing of electrons between the two nitrogen atoms.

Overall, these compounds demonstrate the versatility of nitrogen in forming bonds and its importance in both industrial and natural processes.

Redox Reactions

Redox reactions, or reduction-oxidation reactions, are a type of chemical process where the oxidation states of atoms are changed. This involves the transfer of electrons between chemical species: one species gets oxidized (loses electrons) and the other gets reduced (gains electrons).

To grasp these reactions well, understanding the concepts of **oxidation** and **reduction** and how to identify the changes in oxidation states is key:

• **Oxidation** refers to the loss of electrons by a molecule, atom, or ion. This results in an increase in the oxidation state.
• **Reduction** involves the gain of electrons, leading to a decrease in the oxidation state.

Oxidation states, also known as oxidation numbers, help us keep track of electron transfer in these reactions. In the context of nitrogen compounds, when a nitrogen atom in \(\text{HNO}_3\) with an oxidation state of +5 goes to \(\text{NO}\) with +2, it shows that nitrogen is being reduced (gains electrons), while the opposite process would indicate oxidation.

Redox reactions are crucial in many natural and industrial processes such as respiration, combustion, and corrosion. Identifying oxidation and reduction in chemical formulas helps us understand and predict the outcomes of chemical reactions.

Chemical Equations

Chemical equations represent chemical reactions where reactants convert into products. A well-balanced chemical equation illustrates the conservation of mass and charge, where the mass and total charge are equal on both sides of the equation.

Understanding how to balance these equations is essential in chemistry:

• **Identify all reactants and products**: Write down the chemical formulas for all substances involved.
• **Determine oxidation states**: Knowing the oxidation states helps in identifying the substances undergoing oxidation or reduction in redox reactions.
• **Balance the atoms and charges**: Adjust the coefficients in front of molecules so that the number of atoms and the charges are equal on both sides.

In redox reactions like those involving nitrogen compounds, balance must be achieved not only for the atoms but also for the charges. This ensures that electrons lost by one species (oxidation) are equal to those gained by another (reduction). For example, balancing the charges in the reaction converting \(\text{HNO}_3\) to \(\text{NO}\) ensures proper depiction of the electron transfer between nitrogen oxidation states.

Properly balanced chemical equations are vital for accurate calculations and understanding chemical processes in both laboratories and real-world applications.