Problem 44 - A Complete Resource Book in Chemistry for JEE Main

Question

The reaction of \(\mathrm{H}_{2} \mathrm{O}\) with \(\mathrm{X}\) does not liberate gaseous product. Which of the following is \(\mathrm{X}\) ? (a) \(\mathrm{PbO}_{2}\) (b) \(\mathrm{KMnO}_{4} / \mathrm{H}^{+}\) (c) \(\mathrm{PbS}\) (d) \(\mathrm{Cl}_{2}\)

Step-by-Step Solution

Answer

The correct answer is (c) \( \mathrm{PbS} \).

Step 1: Analyze the Options

First, consider each compound in the options to determine the type of reaction they might undergo with water (\( \mathrm{H}_2\mathrm{O} \)). Evaluating their stability and the types of substances they produce is essential.

Step 2: Evaluate Lead Dioxide (PbO2)

Lead dioxide \( \mathrm{PbO}_2 \) can react with water but typically does not liberate gaseous products. It often functions as an oxidizer in acidic solutions rather than releasing a gas.

Step 3: Evaluate Potassium Permanganate (KMnO4 / H+)

\( \mathrm{KMnO}_4 \) in the presence of acid \( \mathrm{H}^+ \) acts as a strong oxidizing agent and may decompose water to produce oxygen gas \( \mathrm{O}_2 \), especially in acidic conditions.

Step 4: Evaluate Lead(II) Sulfide (PbS)

Lead(II) sulfide \( \mathrm{PbS} \) is a relatively inert compound that does not react readily with water to produce gases. Instead, it is typically involved in reactions producing solid products.

Step 5: Evaluate Chlorine (Cl2)

Chlorine gas \( \mathrm{Cl}_2 \) can dissolve in water to form hypochlorous acid and hydrochloric acid, and does not release any additional gases from this reaction.

Step 6: Determine the Correct Answer

Reviewing each substance, \( \mathrm{PbS} \) is the only one that reacts minimally with water and does not produce a gaseous product, making it the correct choice.

Key Concepts

Lead Dioxide

Lead dioxide, with the chemical formula \(\mathrm{PbO}_2\), is an interesting compound commonly used as an oxidizing agent. It has the characteristic of being less reactive with water, meaning it will not typically liberate gaseous products during reactions with water. This property makes lead dioxide unique compared to other compounds that might easily release gases when reacting with water. Instead, \(\mathrm{PbO}_2\) is more likely to participate in reactions in acidic environments, acting as an oxidizer. This means it can accept electrons from other substances, enabling various chemical processes without forming gases. While it's often part of complex reactions, understanding this property helps in predicting its behavior in different chemical environments.

Potassium Permanganate

Potassium permanganate \((\mathrm{KMnO}_4)\) is known for its vibrant purple color and its role as a powerful oxidizing agent. When combined with acidic solutions, such as with the presence of \(\mathrm{H}^+\), it can cause the decomposition of water, which leads to the production of oxygen gas \((\mathrm{O}_2)\).

• Potassium permanganate's strong oxidizing nature makes it highly reactive, especially under acidic conditions.
• In chemical reactions, it often results in the oxidation of other substances while itself gets reduced to manganese dioxide \((\mathrm{MnO}_2)\).

Understanding the behavior of potassium permanganate in reactions is crucial, particularly for processes like disinfection or oxidation treatments.

Lead(II) Sulfide

Lead(II) sulfide \((\mathrm{PbS})\) is a mineral with a remarkably stable nature, commonly found in its mineral form as galena. It is considered quite inert, especially in reactions with water. This means \(\mathrm{PbS}\) does not easily react with water to produce gases, making it distinct compared to more reactive compounds.

• The stability of lead(II) sulfide contributes to its use in various extraction processes, like obtaining lead metal from its ore.
• When it does react, \(\mathrm{PbS}\) typically results in the formation of solid products instead of gaseous ones.

Due to its inert nature, \(\mathrm{PbS}\) plays a vital role in industrial applications where minimal reaction with ambient conditions is desired.

Chlorine Reaction with Water

Chlorine gas \((\mathrm{Cl}_2)\) possesses a distinct role in reactions with water due to its ability to form acids without releasing additional gases. When dissolved in water, chlorine forms a mixture of hypochlorous acid (HOCl) and hydrochloric acid (HCl).

• This reaction highlights chlorine's utility in water treatment, where the formation of these acids acts as a disinfectant to kill harmful microorganisms.
• Importantly, no gas is liberated from this interaction, maintaining chlorine's role as a critical compound in environmental and public health applications.

Understanding how chlorine functions in aqueous environments emphasizes its significance in sanitation processes, providing insights into its widespread use beyond industrial applications.