Problem 45 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Among the following, the number of compounds than can react with \(\mathrm{PCl}_{5}\) to give \(\mathrm{POCl}_{3}\) is [2011]\mathrm{O}_{2}, \mathrm{CO}_{2}, \mathrm{SO}_{2}, \mathrm{H}_{2} \mathrm{O}, \mathrm{H}_{2} \mathrm{SO}_{4}, \mathrm{P}_{4} \mathrm{O}_{10}

Step-by-Step Solution

Answer

3 compounds: \( \mathrm{H}_2 \mathrm{O} \), \( \mathrm{H}_2 \mathrm{SO}_4 \), \( \mathrm{P}_4 \mathrm{O}_{10} \) can react with \( \mathrm{PCl}_5 \) to form \( \mathrm{POCl}_3 \).

Step 1: Understanding the Reaction

The task is to identify which compounds react with phosphorus pentachloride, \( \mathrm{PCl}_5 \), to form phosphorus oxychloride, \( \mathrm{POCl}_3 \). This typically involves compounds that can act as oxidizing agents or accept electrons to interact with \( \mathrm{PCl}_5 \).

Step 2: Reviewing Each Compound

Let's consider each compound:1. \( \mathrm{O}_2 \) - Oxygen gas doesn't react directly with \( \mathrm{PCl}_5 \) to form \( \mathrm{POCl}_3 \).2. \( \mathrm{CO}_2 \) - Carbon dioxide also does not directly interact with \( \mathrm{PCl}_5 \) to produce \( \mathrm{POCl}_3 \).3. \( \mathrm{SO}_2 \) - Sulfur dioxide does not react to form \( \mathrm{POCl}_3 \).4. \( \mathrm{H}_2 \mathrm{O} \) - Water reacts with \( \mathrm{PCl}_5 \) and is known to form \( \mathrm{POCl}_3 \) in a side reaction as \( \mathrm{PCl}_5 \) hydrolyzes.5. \( \mathrm{H}_2 \mathrm{SO}_4 \) - Sulfuric acid can react with \( \mathrm{PCl}_5 \) to form \( \mathrm{POCl}_3 \).6. \( \mathrm{P}_4 \mathrm{O}_{10} \) - Phosphorus pentoxide does react with \( \mathrm{PCl}_5 \) to form \( \mathrm{POCl}_3 \).

Step 3: Evaluating Possible Reactions

After analyzing, the compounds \( \mathrm{H}_2 \mathrm{O} \), \( \mathrm{H}_2 \mathrm{SO}_4 \), and \( \mathrm{P}_4 \mathrm{O}_{10} \) react with \( \mathrm{PCl}_5 \) to form \( \mathrm{POCl}_3 \). Meanwhile, \( \mathrm{O}_2 \), \( \mathrm{CO}_2 \), and \( \mathrm{SO}_2 \) do not participate in such a reaction.

Key Concepts

Chemical Reactions

Chemical reactions are the processes where substances, called reactants, transform into different substances known as products. In the case of reactions involving phosphorus compounds, especially with phosphorus pentachloride (\( \mathrm{PCl}_5 \)), these reactions often result in the formation of new compounds like phosphorus oxychloride (\( \mathrm{POCl}_3 \)). Several types of reactions can occur, including

• Oxidation-reduction reactions, where electrons are transferred between reactants.
• Hydrolysis reactions, where water is involved in breaking bonds in the reactant.
• Combination reactions, where two or more substances combine to form a single product.

When analyzing a reaction involving \( \mathrm{PCl}_5 \), it's essential to consider the nature of the participating compounds and the possible pathways to form the intended product.

Oxidizing Agents

An oxidizing agent is a substance that gains electrons in a chemical reaction, causing another substance to lose electrons or be oxidized. In the context of phosphorus compounds, compounds that react with \( \mathrm{PCl}_5 \) to form \( \mathrm{POCl}_3 \) often can accept electrons provided in certain situations. For example,

• \( \mathrm{H}_2\mathrm{SO}_4 \) can act as an oxidizing agent when reacting with \( \mathrm{PCl}_5 \).
• Phosphorus pentoxide (\( \mathrm{P}_4\mathrm{O}_{10} \)) also facilitates the conversion of \( \mathrm{PCl}_5 \) into \( \mathrm{POCl}_3 \) by acting as an electron acceptor.

Understanding the role of oxidizing agents helps predict the outcomes of various chemical reactions involving phosphorus pentachloride.

Hydrolysis Reaction

Hydrolysis is a chemical reaction where water breaks down bonds in a molecule. This type of reaction is significant when considering \( \mathrm{PCl}_5 \) because it forms \( \mathrm{POCl}_3 \) in the presence of water:
\[ \mathrm{PCl}_5 + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{POCl}_3 + 2\mathrm{HCl} \]
This process involves the addition of water molecules, which split and rearrange the original compound's structure. Hydrolysis is essential because it reveals how chemical properties change in the presence of water and forms the basis for understanding the interactions and conversions of phosphorus compounds where \( \mathrm{PCl}_5 \) is harnessed to synthesize different products.