Problem 101 - A Complete Resource Book in Chemistry for JEE Main

Question

Identify the compound \((\mathrm{X})\) and the condition (Y) here \(\mathrm{PbS} \stackrel{\text { Heat }}{\longrightarrow}(\mathrm{X})+\mathrm{PbS} \stackrel{(\mathrm{Y})}{\longrightarrow} \mathrm{Pb}+\mathrm{SO}_{2}\) (a) \(\mathrm{X}=\mathrm{PbSO}_{3}, \mathrm{Y}=\) low temperature (b) \(\mathrm{X}=\mathrm{PbO}\) or \(\mathrm{PbSO}_{4}, \mathrm{Y}=\) high temperature (air supply is cut off) (c) \(\mathrm{X}=\mathrm{Pb}_{3} \mathrm{O}_{4}, \mathrm{Y}=\) high temperature (d) \(\mathrm{X}=\mathrm{PbSO}_{4}, \mathrm{Y}=\mathrm{N}_{2}\)

Step-by-Step Solution

Answer

(b) \(\mathrm{X}=\mathrm{PbO}\) or \(\mathrm{PbSO}_{4}\), \(\mathrm{Y}=\) high temperature (air supply is cut off)

Step 1: Analyze Initial Reaction

First, consider the initial reaction \(\mathrm{PbS} \stackrel{\text {Heat}}{\longrightarrow}(\mathrm{X})+\mathrm{PbS}\). Heating lead sulfide (PbS) in air will typically produce lead oxide (PbO) or lead sulfate (\(\mathrm{PbSO}_4\)) as one of the products alongside unreacted PbS.

Step 2: Analyze Subsequent Reaction

Next, analyze the second part of the sequence: \( (\mathrm{X})+\mathrm{PbS} \stackrel{(\mathrm{Y})}{\longrightarrow} \mathrm{Pb}+\mathrm{SO}_{2} \). This reaction indicates the reduction of \( (\mathrm{X}) \) with PbS leading to the formation of metallic lead and sulfer dioxide. This is consistent with the presence of lead oxide or lead sulfate as \( (\mathrm{X}) \), which are commonly reduced to elemental lead under certain conditions.

Step 3: Determine Suitable Conditions

Given the second reaction produces \(\mathrm{Pb}\) and \(\mathrm{SO}_{2}\), a high temperature without air (or limited air supply) promotes reduction and the formation of \(\mathrm{PbO}\) from the sulfide oxidation process can further be reduced by the remaining PbS to liberate Pb and \(\mathrm{SO}_{2}\).

Step 4: Verify Options

Option (b) states: \(\mathrm{X}=\mathrm{PbO}\) or \(\mathrm{PbSO}_{4}\), \(\mathrm{Y}=\) high temperature (air supply is cut off). This matches both the types of products formed during heating of PbS and the conditions under which they convert to lead and SO2.

Key Concepts

Lead Sulfide Reactions

Lead sulfide, or PbS, is a compound that reacts under thermal conditions to form different products. When PbS is heated, it can oxidize and form lead oxide (PbO) or lead sulfate (PbSO₄), depending on the availability of oxygen in the environment. These reactions are fundamental in understanding how sulfide ores are processed in inorganic chemistry.

• In the presence of an excess of oxygen, PbS will likely oxidize to PbSO₄.
• When oxygen is limited, PbO is more commonly produced.

Understanding these reactions is crucial, as they dictate the type of lead compound formed, which further dictates the subsequent chemical reactions they undergo in industrial and laboratory settings.

Reduction Reaction Conditions

Reduction reactions often require specific conditions to proceed effectively. In the case of reducing compounds such as lead oxide or lead sulfate using lead sulfide, understanding these conditions is vital.
For the reduction of lead compounds, typically:

• High temperatures are necessary. The thermal energy supplied helps the reaction to overcome any activation energy barriers.
• Absence of air, or limited oxygen supply, prevents re-oxidation of products or reactants, which can be counterproductive.

These conditions facilitate the conversion of lead oxide or sulfate back to metallic lead and sulfur dioxide, the desired products of such reductions. Thus, the oxidation environment from the first step is reversed to focus on extracting the pure metal.

Inorganic Chemistry Reactions

Inorganic chemistry deals with the reactions and properties of inorganic compounds. Lead and its compounds serve as a classic example to illustrate important concepts in this field.
Reactions involving inorganic compounds such as PbS exemplify several key principles:

• Redox reactions, where oxidation and reduction occur, changing the oxidation states of the substances involved.
• Formation and decomposition of compounds under varying thermal and respiratory conditions.

The reactions of lead sulfide not only reinforce redox chemistry concepts but also underscore the importance of reaction conditions in determining product yield and composition. Each step involves fundamental inorganic chemistry principles, valuable for understanding broader chemical processes in terms of both theoretical and practical applications.