Problem 114 - A Complete Resource Book in Chemistry for JEE Main

Question

A substance 'A' is obtained by boiling an aqueous solution of \(\mathrm{NH}_{3}\) with an aqueous solution of sodium hypochlorite in the presence of a little glue. 'A' forms salts with \(\mathrm{HCl}\) and \(\mathrm{H}_{2} \mathrm{SO}_{4} \cdot^{'} \mathrm{~A}^{\prime}\) is a powerful reducing agent and reduces \(\mathrm{FeCl}_{3}\) solution and acidified \(\mathrm{KMnO}_{4}\) solution. This reaction is being accompanied by evolution of inactive gas ' \(\mathrm{B}\) '. Identify 'A' and ' \(\mathrm{B}\) '. (a) \(\mathrm{A}=\mathrm{O}_{3} ; \mathrm{B}=\mathrm{H}_{2} \mathrm{O}_{2}\) (b) \(\mathrm{A}=\mathrm{NH}_{2} \cdot \mathrm{NH}_{2} ; \mathrm{B}=\mathrm{N}_{2}\) (c) \(\mathrm{A}=\mathrm{N}_{2} ; \mathrm{B}=\mathrm{NO}_{2}\) (d) \(\mathrm{A}=\mathrm{N}_{3} \mathrm{H} ; \mathrm{B}=\mathrm{N}_{2}\)

Step-by-Step Solution

Answer

A is hydrazine (NH}_2NH}_2), and B is nitrogen (N}_2). Option (b) is correct.

Step 1: Analyze the chemical reaction

The reaction of boiling ammonia (NH}_3) with sodium hypochlorite (NaOCl) is known to produce hydrazine (NH}_2NH}_2) in the presence of a little adhesive like glue, which serves as a stabilizer to manage the reaction kinetics.

Step 2: Determine properties of 'A'

'A' forms salts with both hydrochloric acid (HCl) and sulfuric acid (H}_2SO}_4), indicating that it has a basic nature, typical of hydrazine (NH}_2NH}_2). Additionally, hydrazine is a powerful reducing agent, which aligns with the characteristic of 'A' being able to reduce FeCl}_3 and acidified KMnO}_4.

Step 3: Analyze the evolution of gas 'B'

The reaction is accompanied by the evolution of an inactive gas 'B'. In this context, 'inactive' implies a gas that does not react easily, such as nitrogen (N}_2), which is commonly generated as a byproduct during the production of hydrazine.

Step 4: Cross-check with given options

Among the given options, hydrazine (NH}_2NH}_2) for 'A' and nitrogen (N}_2) for 'B' match perfectly with option (b), as hydrazine is known to be formed in this reaction and release nitrogen gas.

Key Concepts

Hydrazine Formation

Hydrazine, with the chemical formula \(NH_2NH_2\), is formed through the interaction of ammonia \(NH_3\) and sodium hypochlorite \(NaOCl\). This reaction is notable due to its industrial significance. The presence of glue in the reaction acts as a stabilizer, managing the formation rate of hydrazine by impacting the reaction kinetics. Hydrazine is a colorless, highly reactive substance used in various applications, such as fuel for rockets and a precursor to polymers. It’s crucial to understand that hydrazine is formed by the oxidation of ammonia, where oxygen from sodium hypochlorite interacts with nitrogen in ammonia. The reaction should be carefully controlled, as hydrazine's volatility and reactivity make it a hazardous compound in uncontrolled environments.

Oxidation-Reduction Reactions

The transformation of ammonia into hydrazine involves an oxidation-reduction (redox) reaction. In redox reactions, electrons are transferred from one species to another. Ammonia acts as a reducing agent, donating electrons, while sodium hypochlorite acts as an oxidizing agent, accepting electrons.

• Oxidation: Ammonia loses electrons, undergoing oxidation.
• Reduction: Sodium hypochlorite gains electrons, undergoing reduction.

Understanding these electron transfer processes is crucial for grasping the nature of chemical reactions. In the specific reaction forming hydrazine, ammonia is oxidized to form the \(N-N\) bond characteristic of hydrazine. This bond formation highlights the importance of electron exchange in driving chemical transformations.

Gas Evolution

During the hydrazine formation process, an inactive gas is also produced, which is nitrogen \(N_2\). Gas evolution is an important aspect of many chemical reactions, where gases formed as byproducts can act as indicators of reaction progress. In this case, nitrogen gas doesn't react with other compounds in the system, which is why it's described as 'inactive'. The production of nitrogen gas during the reaction can be explained by the decomposition of intermediate nitrogen compounds that result from the reduction processes. The escape of nitrogen into the atmosphere is an essential part of the reaction’s completion, helping to drive the reaction forward and prevent the accumulation of unwanted or potentially dangerous intermediates.

Reaction with Sodium Hypochlorite

Sodium hypochlorite \(NaOCl\) is a common household chemical often used in bleaching and disinfection. In the context of hydrazine production, it serves as an oxidizing agent, playing a crucial role in the formation of hydrazine from ammonia.

• Functionality: It provides the necessary chlorine for the reaction, which helps to facilitate the oxidation of ammonia.
• Importance in Industry: This makes the reaction not only interesting for laboratory synthesis but also economically viable in larger-scale applications where bleach availability comes into play.

Understanding the role of sodium hypochlorite offers insight into how simple household chemicals can engage in complex industrial chemical reactions, showcasing the versatility of common substances in chemical synthesis.