Problem 13 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The unbalanced chemical reactions given in List I show missing reagent or condition (?) which are provided in List II. Match List I with List II and select the correct answer using the code given below the lists [Adv. 2013-II] List I List II P. \(\mathrm{PbO}_{2}+\mathrm{H}_{2} \mathrm{SO}_{4} \stackrel{?}{\longrightarrow}\) 1\. \(\mathrm{NO}\) \(\mathrm{PbSO}_{4}+\mathrm{O}_{2}+\) other product Q. \(\quad \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}+\mathrm{H}_{2} \mathrm{O} \stackrel{?}{\longrightarrow}\) 2\. \(\quad I_{2}\) \(\mathrm{NaHSO}_{4}+\) other product R. \(\quad \mathrm{N}_{2} \mathrm{H}_{4} \stackrel{?}{\longrightarrow} \mathrm{N}_{2}+\) other product 3\. Warm S. \(\quad \mathrm{XeF}_{2} \stackrel{?}{\longrightarrow} \mathrm{Xe}+\) other product 4\. \(\mathrm{Cl}_{2}\)Codes : \(\mathrm{P} \mathrm{Q} \mathrm{R} \mathrm{S}\) (a) \(\quad 4231\) (b) 3214 (c) 1423 (d) \(\quad 34421\)

Step-by-Step Solution

Answer

The correct code is (a) 4231.

Step 1: Analyzing Reaction P

The given reaction is \( \mathrm{PbO}_2 + \mathrm{H}_2\mathrm{SO}_4 \rightarrow \ \mathrm{PbSO_4} + \mathrm{O}_2 + \ \text{other product} \). The missing condition or reagent is needed to release \( \mathrm{O}_2 \) from \( \mathrm{PbO}_2 \). In this reaction, the presence of \( \mathrm{Cl}_2 \) is necessary to oxidize and split \( \mathrm{PbO}_2 \), hence the missing reagent is \( \mathrm{Cl}_2 \). So, the match is 4.

Step 2: Analyzing Reaction Q

For the reaction \( \mathrm{Na}_2 \mathrm{~S}_2 \mathrm{O}_3 + \mathrm{H}_2 \mathrm{O} \rightarrow \ \mathrm{NaHSO}_4 + \ \text{other product} \), the presence of \( \mathrm{I}_2 \) is needed because \( \mathrm{Na}_2\mathrm{S}_2\mathrm{O}_3 \) reacts with \( \mathrm{I}_2 \) in aqueous solution to form \( \mathrm{NaHSO}_4 \) and other products. Therefore, the answer is 2.

Step 3: Analyzing Reaction R

The reaction \( \mathrm{N}_2\mathrm{H}_4 \rightarrow \ \mathrm{N}_2 + \ \text{other product} \) involves the decomposition of hydrazine. This reaction typically requires heat, so the correct condition is 'warm.' The match for this reaction is 3.

Step 4: Analyzing Reaction S

The reaction \( \mathrm{XeF}_2 \rightarrow \ \mathrm{Xe} + \ \text{other product} \) involves the decomposition of xenon difluoride. This decomposition can occur naturally, typically requiring a warm environment. Therefore, the right condition is 'warm', which corresponds to 3.

Step 5: Matching List I with List II

From the analysis:- P: 4 (\( \mathrm{Cl}_2 \))- Q: 2 (\( \mathrm{I}_2 \))- R: 3 (warm)- S: 3 (warm)The correct sequence of matches is \(4231\).

Key Concepts

Chemical Reactions

Chemical reactions are processes where substances called reactants transform into different substances known as products. During a chemical reaction, the atoms in the reactants rearrange to form new products. This change is often accompanied by observable macroscopic events such as color changes, temperature fluctuations, or gas production.

In the problem provided, several chemical reactions were presented with missing reagents or conditions needed to complete them. Each reaction involved has its specific stoichiometry and requirements for the reaction to proceed. Balancing these reactions is key, as it ensures the conservation of mass, meaning the total mass of reactants equals the total mass of products.

Reaction Conditions

Reaction conditions refer to the environment and specific criteria required for a chemical reaction to occur efficiently. These conditions can include temperature, pressure, the presence of catalysts or specific reagents, or even the physical state of the reactants.

In the exercise, identifying the reaction conditions was crucial. For example, in Reaction P, the presence of chlorine (\( \mathrm{Cl}_2\)) is needed as an additional reactant to facilitate the transformation and release of oxygen from \( \mathrm{PbO}_2\). Similarly, in Reaction R and S, the mention of 'warm' indicates that heat is necessary to drive the decomposition reactions forward.

Oxidation and Reduction

Oxidation and reduction are complementary chemical processes often called redox reactions. During oxidation, a substance loses electrons, while in reduction, a substance gains electrons. These processes are critical in chemical reactions as they allow the formation of new substances.

In Reaction P, oxidation plays a key role where \( \mathrm{PbO}_2\) is oxidized with the help of \( \mathrm{Cl}_2\), enabling the release of oxygen gas. Such processes are vital in industrial and laboratory settings for the synthesis of new materials and the understanding of chemical behavior.

Decomposition Reactions

Decomposition reactions involve the breakdown of a single compound into two or more simpler substances. These reactions often require energy input like heat, light, or electricity to overcome the energy barrier for the decomposition to occur.

In the provided exercise, Reaction R and Reaction S are classic examples of decomposition reactions. In Reaction R, hydrazine (\( \mathrm{N}_2 ext{H}_4\)) decomposes into nitrogen gas and other products, typically triggered by warmth. Likewise, in Reaction S, xenon difluoride (\( \mathrm{XeF}_2\)) decomposes into xenon and other products under warm conditions. These reactions emphasize the application of energy in breaking down compounds.