Problem 92 - A Complete Resource Book in Chemistry for JEE Main

Question

The chemical reaction, \(2 \mathrm{AgCl}(\mathrm{s})+\mathrm{H}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{HCl}(\mathrm{aq})+2 \mathrm{Ag}(\mathrm{s})\) taking place in a galvanic cell is represented by the notation (a) \(\mathrm{Pt}(\mathrm{s}) \mid \mathrm{H}_{2}(\mathrm{~g}), 1\) bar \(\mid 1 \mathrm{M} \mathrm{KCl}\) (aq) \(|\mathrm{AgCl}(\mathrm{s})| \mathrm{Ag}\) (s) (b) \(\mathrm{Pt}(\mathrm{s})\left|\mathrm{H}_{2}(\mathrm{~g}), 1 \mathrm{bar}\right| 1 \mathrm{M} \mathrm{KCl}(\mathrm{aq})\left|1 \mathrm{M} \mathrm{Ag}^{+}(\mathrm{aq})\right|\) \(\mathrm{Ag}(\mathrm{s})\) (c) \(\mathrm{Pt}(\mathrm{s}) \mid \mathrm{H}_{2}(\mathrm{~g}), 1\) bar \(\mid 1 \mathrm{M} \mathrm{KCl}\) (aq) \(|\mathrm{AgCl}(\mathrm{s})| \mathrm{Ag}\) (s) (d) \(\mathrm{Pt}(\mathrm{s})\left|\mathrm{H}_{2}(\mathrm{~g}), 1 \mathrm{bar}\right| 1 \mathrm{M} \mathrm{KCl}\) (aq) \(|\mathrm{Ag}(\mathrm{s})| \mathrm{AgCl}\)

Step-by-Step Solution

Answer

The correct notation is (a) and (c).

Step 1: Identify the oxidation and reduction processes

In this galvanic cell reaction, AgCl is reduced to Ag, and H2 is oxidized to form HCl. This indicates the cathode involves the reduction of AgCl to Ag, and the anode involves the oxidation of H2 into H+ as part of HCl.

Step 2: Structure the cell notation

Galvanic cell notation is represented as \( ext{Anode} \ ext{Electrolyte} \ ext{Cathode}\). Therefore, we start the notation with hydrogen which is at the anode, then move to the electrolyte, and finally, to silver chloride reduction at the cathode.

Step 3: Use the provided notations to identify the correct one

Analyze each option: - (a) It correctly shows the structure of the cell with hydrogen at the anode and AgCl to Ag conversion at the cathode. - (b) Incorrect, this notation doesn't show the AgCl solid properly in the reaction. - (c) This is a repeat of option (a) and is formatted correctly showing the anode and cathode. - (d) This shows the electrode-agitation inconsistent with our reaction, indicating an incorrect anode/cathode layout.

Step 4: Choose the correct notation

Both options (a) and (c) are formatted correctly with the notation structure and reflect the galvanic cell reaction accurately.

Key Concepts

Oxidation and Reduction Process

Understanding the oxidation and reduction process is vital in grasping the concept of a galvanic cell. In the given chemical reaction, AgCl (silver chloride) is reduced to Ag (silver). This signifies that silver chloride gains electrons to become metallic silver, representing a reduction process because reduction involves gaining electrons. On the flip side, hydrogen gas (H\(_2\)) is oxidized to form hydrochloric acid (HCl), where it loses electrons to form hydrogen ions (H\(^+\)). Hence, oxidation is characterized by the loss of electrons. The term 'redox reaction' arises from this electron transfer process, combining both reduction and oxidation.

• Reduction: Occurs at the cathode. Electrons are gained.
• Oxidation: Takes place at the anode. Electrons are lost.

These processes are essential as they drive the flow of electrons, which is a hallmark of electricity generation in a galvanic cell. They are the very foundation of what powers the electrochemical processes.

Electrochemical Cell Structure

The structure of an electrochemical cell, specifically a galvanic cell, is crucial for its operation. A galvanic cell consists of two half-cells, each containing a conductor and an electrolyte. These are connected by a salt bridge or a porous disk to allow ion flow. The anode is where oxidation happens, while the cathode is the site of reduction. In our reaction, the anode is where hydrogen gas (H\(_2\)) gets oxidized, and the cathode is where silver chloride (AgCl) gets reduced.

• Anode: The site of oxidation, producing electrons.
• Cathode: The location of reduction, consuming electrons.
• Salt Bridge: Maintains charge balance by permitting ion flow.

Proper structure ensures electrons travel through the external circuit, creating a usable electric current. The pathways and processes within each segment of the galvanic cell are designed to facilitate electron flow and sustain the chemical reactions.

Half-cell Reactions

In any galvanic cell, the cell is split into two half-cells, each featuring its own unique half-reaction. These reactions occur in separate compartments and contribute to overall cell function. For our particular exercise:At the **anode**, we have the half-reaction:\[ H_2(g) \rightarrow 2H^+(aq) + 2e^- \]Here, hydrogen gas is oxidized to produce protons and electrons.At the **cathode**, the half-reaction is:\[ AgCl(s) + e^- \rightarrow Ag(s) + Cl^-(aq) \]This shows silver chloride being reduced to silver, gaining electrons in the process.The flow of electrons from anode to cathode is what generates electrical energy in a galvanic cell.

• Anode Half-Reaction: Oxidation, electron release, hydrogen as a reactant.
• Cathode Half-Reaction: Reduction, electron gain, involving silver chloride.

By understanding half-cell reactions, one can predict the flow and balance of electrons, allowing for accurate prediction of the direction and functionality of the entire cell.