Problem 33 - A Complete Resource Book in Chemistry for JEE Main

Question

By removing a salt bridge between the two half cells, the voltage (a) increase gradually (b) increase rapidly (c) does not change (d) drops to zero

Step-by-Step Solution

Answer

(d) drops to zero.

Step 1: Understanding the Role of a Salt Bridge

A salt bridge is a vital component of a galvanic cell that is used to maintain electrical neutrality within the internal circuit. It allows the flow of ions and completes the circuit, which is crucial for the cell to function properly.

Step 2: Predicting the Effect of Removing the Salt Bridge

If the salt bridge is removed, the flow of ions between the half-cells is disrupted. This imbalance prevents the continuation of the redox reactions necessary for generating an electromotive force (EMF). Without ion flow, charge buildup occurs, halting electron flow through the circuit.

Step 3: Conclusion on Effect on Voltage

When the salt bridge is removed, the circuit is effectively broken, and electron flow stops. As a result, the voltage of the cell drops to zero since no electrical current can pass through the circuit.

Key Concepts

galvanic cell

A galvanic cell, also known as a voltaic cell, forms the foundation of understanding basic electrochemical reactions. It is a device that converts chemical energy into electrical energy through a spontaneous redox reaction. Imagine a galvanic cell as a simple battery consisting of two different metal electrodes submerged in respective electrolyte solutions. Each of these setups is called a half-cell.

In a galvanic cell, you'll typically find:

• Two electrodes (often a metal rod or strip) — one acts as the anode (where oxidation happens), and the other as the cathode (where reduction occurs).
• Electrolyte solutions that allow ions to move and participate in the reactions.
• A salt bridge that connects the two half-cells, maintaining charge balance.

These elements work together to ensure the flow of electrons, completing the circuit and enabling the galvanic cell to function as a source of power.

salt bridge

The salt bridge is an essential part of a galvanic cell, playing a crucial role in maintaining electrical neutrality. Consider it as the glue that holds the system together, allowing the cell to continue functioning smoothly. It is typically a tube containing a gel saturated with an inert electrolyte, like potassium nitrate or potassium chloride.

The primary role of a salt bridge is:

• To allow the movement of ions between the half-cells to balance out charges.
• To prevent the direct mixing of different electrolytes, which could interfere with the reactions.

When the salt bridge is removed or disrupted, the circuit breaks, halting the energy conversion process. This leads to a stoppage in electron flow, causing the voltage to plummet to zero, as seen in the step-by-step solution provided in the exercise.

electromotive force (EMF)

Electromotive force (EMF) is a fundamental concept in electrochemistry, representing the potential difference across the terminals of a galvanic cell. Though referred to as a "force," it is actually a measure of energy provided by the cell, driving the movement of electrons through the circuit.

Key points about EMF include:

• It is measured in volts, indicating the electric potential work done per unit charge.
• EMF is determined by the specific materials and reactions taking place within the electrodes and electrolytes.
• A higher EMF suggests a greater ability for the cell to drive electrons, and hence, provide electricity.

In the context of the exercise, the removal of the salt bridge interrupts the redox reactions that produce EMF, leading to an immediate drop to zero voltage due to the stoppage of electron flow. Understanding EMF helps explain why maintaining a fully intact circuit is crucial for the operation of galvanic cells.