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) \(4 \mathrm{NH}_{3}+5 \mathrm{O}_{2} \stackrel{750^{\circ} \mathrm{C}-900^{\circ} \mathrm{C}, \text { catalyst }}{\longrightarrow} 4 \mathrm{NO}+6 \mathrm{H}_{2} \mathrm{O}\) \(\mathrm{NO} \stackrel{\text { heat } \mathrm{O}_{2}}{\longrightarrow} \mathrm{NO}_{2} \stackrel{\mathrm{H}_{2} \mathrm{O}}{\mathrm{O}} \mathrm{HNO}_{3}\) (b) \(\mathrm{S}+\mathrm{O}_{2} \longrightarrow \mathrm{SO}_{2} \stackrel{\mathrm{O}_{2}}{\longrightarrow} \mathrm{SO}_{3} \frac{3}{+\mathrm{HNO}_{3}}\) \(\longrightarrow \mathrm{NaNO}_{3}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{NaHSO}_{4}\) (d) both (a) and (b)

Step-by-Step Solution

Answer

The correct sequence is option (a).

Step 1: Understand the Ostwald Process

The Ostwald process is an industrial chemical process used to manufacture nitric acid. The process primarily involves the catalytic oxidation of ammonia (NH₃) to nitrogen dioxide (NO₂), followed by the absorption of NO₂ in water to produce nitric acid (HNO₃). The key reactions include NH₃ oxidation to form NO, and NO oxidation to NO₂, followed by the absorption of NO₂ in water.

Step 2: Analyze Each Given Reaction

Look at reaction (a): 1. Ammonia (NH₃) reacts with oxygen (O₂) to form nitric oxide (NO) and water (H₂O) (Step 1 of Ostwald Process). 2. Nitric oxide (NO) is further oxidized to nitrogen dioxide (NO₂) (Step 2 of Ostwald Process). 3. Nitrogen dioxide reacts with water to form nitric acid (HNO₃) (Step 3 of Ostwald Process). Reaction (b) does not involve ammonia oxidation and is related to sulfuric acid production, not nitric acid.

Step 3: Identify the Correct Sequence

Compare the described Ostwald process (step-by-step oxidation of NH₃ to NO and NO to NO₂, followed by NO₂'s transformation to HNO₃) with the reactions provided in options (a) and (b). Option (a) follows the Ostwald process exactly, whereas (b) involves sulfur reactions not related to nitric acid manufacture.

Step 4: Select the Correct Answer

Based on the analysis, option (a) represents the correct sequence for the Ostwald process. It correctly describes the reactions starting from the oxidation of ammonia to the production of nitric acid.

Key Concepts

Industrial Chemical Processes

Industrial chemical processes play a major role in modern manufacturing and production. These processes involve chemical reactions on a large scale, efficiently converting raw materials into valuable products. In industry, speed, efficiency, and cost are pivotal factors, making established chemical processes vital for producing products we rely on daily.

One hallmark of successful industrial chemical processes is their ability to operate continuously and safely under controlled conditions. They usually require specific temperatures, pressures, and catalysts to proceed optimally. For instance, ammonia oxidation in the Ostwald process is operated under high temperatures and involves specific catalysts to ensure that ammonia is efficiently oxidized into the desired products.

Common examples include:

• The Haber process for ammonia production.
• Hall-Héroult process for aluminum extraction.
• The Ostwald process for nitric acid production.

These processes not only contribute to the bulk chemical production but also significantly impact fields such as agriculture with fertilizers and various industries with extracts and reagents.

Nitric Acid Manufacture

Nitric acid is an essential chemical, widely used in fertilizers, explosives, and many industrial applications. The primary industrial method for its production is the Ostwald process, which efficiently converts ammonia into nitric acid.

The Ostwald process involves three main steps:

• Oxidation of ammonia (\( \text{NH}_3 + \text{O}_2 \rightarrow \text{NO} + \text{H}_2\text{O} \))
  This step is conducted at high temperatures, usually between 750°C and 900°C, and uses a platinum-based catalyst to speed up the reaction.
• Further oxidation of nitric oxide (\( \text{NO} + \text{O}_2 \rightarrow \text{NO}_2 \))
  This is a spontaneous reaction where nitric oxide reacts with available oxygen in the air to form nitrogen dioxide.
• Absorption of nitrogen dioxide in water (\( \text{NO}_2 + \text{H}_2\text{O} \rightarrow \text{HNO}_3 \))
  Finally, nitrogen dioxide is absorbed in water to generate nitric acid.

Each of these steps must be carefully controlled to maximize efficiency and yield. Any deviations can impact the production volume and purity of the nitric acid produced.

Catalytic Oxidation of Ammonia

Catalytic oxidation of ammonia is a critical reaction within the Ostwald process for nitric acid manufacture. Here, the goal is to convert ammonia into nitric oxide, a precursor for further reactions leading to nitric acid.

Several factors make this reaction unique:

• High temperature operation:
  The reaction is conducted at temperatures ranging from 750°C to 900°C. High temperatures are necessary to achieve the desired reaction speed and efficiency.
• Use of a catalyst:
  A platinum catalyst is crucial for the oxidation of ammonia to nitric oxide. Catalysts are substances that increase the reaction rate without being consumed in the process, making the reaction economically viable.
• Exothermic nature:
  This reaction releases heat, which can be harnessed to power other parts of the process or to maintain reaction conditions.

Without catalysis, the oxidation of ammonia would be too slow and inefficient for industrial purposes. The catalyst lowers the activation energy required, allowing the reaction to proceed rapidly even under stringent economic conditions. This step is fundamental in creating a seamless, efficient manufacturing process for nitric acid.