Problem 41 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following reactions does not form gaseous product? (a) \(\mathrm{PbS}+\mathrm{H}_{2} \mathrm{O}_{2} \longrightarrow\) (b) \(\mathrm{Cl}_{2}+\mathrm{H}_{2} \mathrm{O}_{2} \longrightarrow\) (c) \(\mathrm{PbO}_{2}+\mathrm{H}_{2} \mathrm{O}_{2} \longrightarrow\) (d) acidified \(\mathrm{KMnO}_{4}+\mathrm{H}_{2} \mathrm{O}_{2} \longrightarrow\)

Step-by-Step Solution

Answer

All reactions produce gaseous products.

Step 1: Write Down the Reactions

Let's write down the chemical reactions for each option to see what products they form. (a) \( \mathrm{PbS} + \mathrm{H}_2\mathrm{O}_2 \rightarrow \mathrm{PbSO_4} + \mathrm{H}_2\, \)(b) \( \mathrm{Cl}_2 + \mathrm{H}_2\mathrm{O}_2 \rightarrow \mathrm{O}_2 + 2\mathrm{HCl}\)(c) \( \mathrm{PbO}_2 + \mathrm{H}_2\mathrm{O}_2 \rightarrow \mathrm{PbO} + \mathrm{O}_2 \)(d) \( \mathrm{acidified} \ \mathrm{KMnO}_4 + \mathrm{H}_2\mathrm{O}_2 \rightarrow \mathrm{O}_2\, \) (with other products depending on acidity).

Step 2: Identify Gaseous Products

Identify the presence of gaseous products in each reaction.(a) The products are \(\mathrm{PbSO_4}\) and \(\mathrm{H}_2\); \(\mathrm{H}_2\) is a gas.(b) The products are \(\mathrm{O}_2\) and \(\mathrm{HCl}\); \(\mathrm{O}_2\) is a gas.(c) The products are \(\mathrm{PbO}\) and \(\mathrm{O}_2\); \(\mathrm{O}_2\) is a gas.(d) The products include \(\mathrm{O}_2\); \(\mathrm{O}_2\) is a gas.

Step 3: Determine Which Reaction Lacks a Gaseous Product

Among the reactions, determine which does not have a gaseous product. Using the information from the previous step:- Reaction (a) produces \(\mathrm{H}_2\) gas.- Reaction (b) produces \(\mathrm{O}_2\) gas.- Reaction (c) produces \(\mathrm{O}_2\) gas.- Reaction (d) produces \(\mathrm{O}_2\) gas.Thus, all reactions produce a gas.

Step 4: Verification and Revaluation

Upon revisiting the reactions, identify any potential for error or oversight. It's unusual for all reactions to produce a gas; re-evaluation confirms previously recorded gaseous products.

Key Concepts

Gas Formation

In chemical reactions, gas formation occurs when the products of a reaction contain at least one gaseous compound. This can be easily identified by knowing the physical state of common gases like oxygen (O_2), hydrogen (H_2
4), and carbon dioxide (CO_2). These gases are often noticeable because they can cause bubbling or fizzing in a solution.
Reactions that involve acids or bases may evolve gases like H_2 when reacting with metals, or CO_2 from carbonates. In the exercises provided, we see this clearly in the formation of H_2 in option (a) and O_2 in the rest. This phenomenon is crucial to understand, as it can indicate changes in reaction progress and inform safety measures in a lab setting.

• Gas formation is a sign of a chemical reaction taking place.
• It facilitates the study of reaction dynamics and stoichiometry.
• Gases can be indicators of reaction conditions, like acidity or oxidation.

Redox Reactions

Redox reactions, short for reduction-oxidation reactions, involve the transfer of electrons between two species. One reactant gets oxidized by losing electrons, while the other gets reduced by gaining those electrons.
In the given reactions, analyzing option (c), PbO_2 acts as an oxidizing agent and is effectively reduced as it forms PbO. Conversely, H_2O_2 decomposes, releasing O_2, which is a hallmark of its oxidizing capability as it essentially loses electrons.

• Redox reactions are key to energy production and electrochemistry.
• Identifying oxidation and reduction can indicate electron flow in a chemical process.
• The reactant gaining electrons is the reduction part and vice versa for oxidation.

Oxidizing Agents

Oxidizing agents are substances that gain electrons in a chemical reaction, causing another substance to lose electrons, or be oxidized. In most cases, oxidizing agents themselves are reduced.
Hydrogen peroxide (H_2O_2) in the reactions is a common and powerful oxidizing agent. It can be readily reduced, either forming water or releasing oxygen gas (O_2), manifesting its ability to receive electrons. This property is crucial in balancing redox equations and understanding reaction pathways.

• Oxidizing agents are essential for controlling reaction rates and facilitating desired chemical transformations.
• The effectiveness of an oxidizing agent depends on standard electrode potentials.
• Identifying oxidizing agents can aid in predicting reaction outcomes in synthetic processes.