Problem 100 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following reactions shows the correct sequence of the Ostwald process in the manufacture of nitric acid? (a) \(4 \mathrm{NH}_{3}+5 \mathrm{O}_{2} \stackrel{750^{\circ} \mathrm{C}-900^{\circ} \mathrm{C} \text {, catalyst }}{\longrightarrow} 4 \mathrm{NO}+6 \mathrm{H}_{2} \mathrm{O}\) \(\mathrm{NO} \stackrel{\text { heat } \mathrm{O}_{2}}{\longrightarrow} \mathrm{NO}_{2} \stackrel{\mathrm{H}_{2} \mathrm{O}}{\longrightarrow} \mathrm{HNO}_{3}\) (b) \(\mathrm{S}+\mathrm{O}_{2} \longrightarrow \mathrm{SO}_{2} \stackrel{\mathrm{O}_{2}}{\longrightarrow} \mathrm{SO}_{3} \stackrel{3}{\stackrel{\mathrm{H}}_{2} \mathrm{O}}{+\mathrm{HNO}_{3}}\) \(\longrightarrow \mathrm{NaNO}_{3}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{NaHSO}_{4}\) (c) \(\mathrm{N}_{2}+\mathrm{O}_{2} \stackrel{\text { Low temp, high pressure }}{\longrightarrow} 2 \mathrm{NO}+\) heat \(\stackrel{\mathrm{O}_{2}, \text { catalyst }}{\longrightarrow} \mathrm{NO}_{2} \stackrel{\mathrm{H}_{2} \mathrm{O}}{\longrightarrow} \mathrm{HNO}_{3}\) (d) both (b) (a) and

Step-by-Step Solution

Answer

Option (a) is correct.

Step 1: Identify the Ostwald Process

The Ostwald process is an industrial process for the production of nitric acid (HNO3), starting from ammonia (NH3). The main stages involved are: (1) oxidation of ammonia to nitric oxide (NO), (2) oxidation of nitric oxide to nitrogen dioxide (NO2), and (3) absorption of nitrogen dioxide in water to produce nitric acid.

Step 2: Analyze Reaction Sequence in Option (a)

In option (a), the provided reactions are:1. \(4 \mathrm{NH}_{3} + 5 \mathrm{O}_{2} \rightarrow 4 \mathrm{NO} + 6 \mathrm{H}_{2} \mathrm{O}\)2. \(\mathrm{NO} \rightarrow \mathrm{NO}_{2} \rightarrow \mathrm{HNO}_{3}\)This sequence follows the Ostwald steps: ammonia is oxidized to nitric oxide, nitric oxide is oxidized to nitrogen dioxide, and nitrogen dioxide is absorbed by water to produce nitric acid.

Step 3: Analyze Reaction Sequence in Option (b)

In option (b), sulfur is used instead of ammonia:1. \( \mathrm{S} + \mathrm{O}_{2} \rightarrow \mathrm{SO}_{2} \rightarrow \mathrm{SO}_{3} \rightarrow \mathrm{HNO}_{3}\)2. \(\mathrm{NaNO}_{3} + \mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{NaHSO}_{4}\)This does not follow the Ostwald process, as it involves sulfur reactions and mentions \(\mathrm{NaNO}_{3}\), which is unrelated to the Ostwald process for nitric acid production.

Step 4: Determine Correct Option

Only option (a) correctly follows the Ostwald process for the manufacture of nitric acid. Option (b) includes reactions not relevant to the Ostwald process.

Key Concepts

Nitric Acid Production

The production of nitric acid is a fundamental industrial process essential for manufacturing fertilizers, explosives, and other chemicals. The principal method for nitric acid production is the Ostwald process. This entails a series of chemical reactions that convert ammonia into nitric acid. The process starts with ammonia oxidation and is further extended through carefully controlled reaction sequences to ensure maximum yield and efficiency of nitric acid.
In industrial settings, ammonia derived from the Haber process is used as a primary precursor. The key to efficient nitric acid production lies in maintaining optimum temperature and pressure conditions, especially while ensuring the presence of specific catalysts to accelerate the necessary reactions. The end product, nitric acid, is then concentrated and purified for various applications. The chemical reaction must follow an efficient pathway that starts with ammonia, making the Ostwald process distinct from other methods.

Ammonia Oxidation

Ammonia oxidation is the first crucial step in the Ostwald process, a well-known method for nitric acid production. This step involves the conversion of ammonia gas ( "), typically obtained from the Haber-Bosch process, into nitric oxide ( "). This is achieved by reacting ammonia with oxygen at high temperatures, typically between 750°C and 900°C, in the presence of a platinum-rhodium catalyst. The reaction can be represented by: 4 NH₃ + 5 O₂ → 4 NO + 6 H₂O This highly exothermic reaction is not only crucial for the production of nitric oxide but also releases a significant amount of heat energy, which can be harnessed and recycled within the plant. The generated nitric oxide is rapid, enabling continuous throughput in industrial production.
Ammonia oxidation is vital as it sets the foundation for subsequent steps in nitric acid production. Efficient control of reaction conditions, such as temperature and catalyst usage, is necessary to optimize yield and prevent the formation of unwanted by-products.

Chemical Reaction Sequences

Understanding the sequence of chemical reactions is key to mastering industrial chemical processes like the Ostwald process. The sequence begins with ammonia being oxidized to nitric oxide, followed by the conversion to nitrogen dioxide, and ultimately the absorption of nitrogen dioxide in water to form nitric acid. Additionally, this sequence ensures safety, economics, and efficiency.
The chain reaction follows a well-coordinated flow, specifically: - Ammonia is oxidized into nitric oxide: 4 NH₃ + 5 O₂ → 4 NO + 6 H₂O - Nitric oxide is further oxidized to nitrogen dioxide: 2 NO + O₂ → 2 NO₂ - Nitrogen dioxide reacts with water: 3 NO₂ + H₂O → 2 HNO₃ + NO Each stage is vital for the full transformation of reactants into the desired product. In industrial settings, any deviation from this sequence could result in inefficiencies or incomplete reactions, affecting the overall economic feasibility of the process.
Therefore, understanding and meticulously following these reaction sequences is fundamental for chemical engineers to design, operate, and troubleshoot nitric acid production plants effectively.