Problem 75 - A Complete Resource Book in Chemistry for JEE Main

Question

The industrial preparation of nitric acid by Ostwald's process involves (a) hydrolysis of \(\mathrm{NH}_{3}\) (b) reduction of \(\mathrm{NH}_{3}\) (c) hydrogenation of \(\mathrm{NH}_{3}\) (d) oxidation of \(\mathrm{NH}_{3}\)

Step-by-Step Solution

Answer

The Ostwald process involves the oxidation of ammonia (d).

Step 1: Understanding the Ostwald Process

The Ostwald process is a key method for producing nitric acid, which involves several chemical reactions. The primary reaction in this process is the oxidation of ammonia (\( \mathrm{NH}_3 \)). This is typically done in the presence of a platinum-rhodium catalyst at high temperatures.

Step 2: Identifying the Key Reaction

In the Ostwald process, ammonia is first oxidized to form nitric oxide (\( \mathrm{NO} \)) and water. This reaction can be written as:\[\mathrm{4NH}_3 + \mathrm{5O}_2 \rightarrow \mathrm{4NO} + \mathrm{6H}_2\mathrm{O}\]This step is crucial and confirms that ammonia undergoes oxidation.

Step 3: Eliminate Incorrect Options

Given that the Ostwald process involves the oxidation of ammonia, we can eliminate the other options:- (a) Hydrolysis of \( \mathrm{NH}_3 \): Not involved in this process.- (b) Reduction of \( \mathrm{NH}_3 \): Not applicable as \( \mathrm{NH}_3 \) is oxidized, not reduced.- (c) Hydrogenation of \( \mathrm{NH}_3 \): Not relevant here, as this would involve adding hydrogen, not a feature of this process.

Step 4: Confirm the Correct Answer

The correct process involved in the industrial preparation of nitric acid by the Ostwald process is (d) oxidation of \( \mathrm{NH}_3 \). This aligns with the identified chemical reaction of ammonia oxidation in the Ostwald process.

Key Concepts

Oxidation of Ammonia

In the Ostwald process, the oxidation of ammonia marks the initiation of nitric acid production. Ammonia (\( \text{NH}_3 \)) acts as the primary reactant. When it reacts with oxygen (\( \text{O}_2 \)), the molecules rearrange to form nitric oxide (\( \text{NO} \)) and water (\( \text{H}_2\text{O} \)). This reaction is depicted by the equation:\[\mathrm{4NH}_3 + \mathrm{5O}_2 \rightarrow \mathrm{4NO} + \mathrm{6H}_2\mathrm{O}\]The following step leads to the critical formation of nitric oxide, a precursor to nitric acid. The oxidation reaction requires high temperatures, approximately 900°C. It is conducted in a special reaction chamber to maintain optimal efficiency.

• Ammonia oxidizes while oxygen acts as the oxidizing agent.
• This part of the reaction lays the groundwork for further conversion steps towards nitric acid.

Industrial Preparation of Nitric Acid

The Ostwald process is pivotal for nitric acid production on an industrial level. After ammonia is oxidized to nitric oxide, the next steps involve further oxidation and absorption processes to yield the end product. Once nitric oxide (\( \text{NO} \)) is obtained, it undergoes further reactions:1. **Oxidation of Nitric Oxide:** The nitric oxide reacts with additional oxygen to form nitrogen dioxide (\( \text{NO}_2 \)). \[\mathrm{2NO} + \mathrm{O}_2 \rightarrow \mathrm{2NO}_2\] 2. **Absorption in Water:** Nitrogen dioxide is absorbed in water, resulting in the formation of nitric acid (\( \text{HNO}_3 \)) alongside nitrous acid (\( \text{HNO}_2 \)). \[\mathrm{3NO}_2 + \mathrm{H}_2 ext{O} \rightarrow \mathrm{2HNO}_3 + \mathrm{NO}\]Each step systematically increases the concentration of nitric oxide and retains efficiency. Together, these reactions outline the full procedure for industrial nitric acid production, providing a stable output for various applications.

Platinum-Rhodium Catalyst

The use of a platinum-rhodium catalyst is a defining feature of the Ostwald process. Catalysts are substances that increase the rate of chemical reactions without being consumed. In this case, the platinum-rhodium alloy plays a crucial role in speeding up the oxidation of ammonia. Its characteristics include:

• **Durability:** Able to withstand very high temperatures required for the reaction.
• **Efficiency:** Promotes rapid oxidation of ammonia, making the process economically viable.
• **Chemical Stability:** Does not react with the reactants or products, ensuring continual operation over multiple cycles.

The presence of this catalyst significantly reduces the required energy input and helps maintain the purity and yield of nitric oxide. Thus, its use is not just beneficial but essential in the large-scale operations of nitric acid production.