Question

Which is/are correct statement about salt bridge? (a) Ions of salt bridge discharge at electrode (b) Ions of salt bridge do not discharge at electrode (c) Velocity of ions of salt bridge are almost equal (d) Salt bridge complete the electric circuit.

Short answer

The correct statements are (b), (c), and (d).

Step-by-step solution

Understanding Salt Bridge Functionality

A salt bridge is used in an electrochemical cell to maintain electrical neutrality. It allows ions to move between two half-cells, preventing charge buildup that would otherwise stop the cell from functioning.

Examining Ion Discharge

In a functioning salt bridge, ions do not discharge at the electrode. This means the ions from the salt bridge remain in solution and are not consumed in the electrochemical reaction occurring at the electrodes. Therefore, (b) Ions of salt bridge do not discharge at electrode is correct.

Assessing Ion Velocity

The ions in the salt bridge are generally chosen such that they have similar mobility. This helps maintain a neutral charge balance within each half-cell over time. Thus, (c) Velocity of ions of salt bridge are almost equal is generally correct.

Role of Salt Bridge in Circuit Completion

The salt bridge allows the flow of ions, completing the electric circuit in an electrochemical cell. Without it, the circuit would break, and the reaction would stop. Hence, (d) Salt bridge completes the electric circuit is correct.

Finalizing Correct Options

Based on the analysis: (b), (c), and (d) are correct statements about the salt bridge.

Key concepts

Electrochemical Cell

An electrochemical cell is a fascinating device that converts chemical energy into electrical energy through an electrochemical reaction. In simple terms, it is made up of two half-cells, each containing an electrode submerged in an electrolyte solution. Each half-cell involves a different reaction, and these reactions occur at the electrodes.

• The oxidation reaction occurs at the anode, which releases electrons.
• The reduction reaction takes place at the cathode, which gains these electrons.

The electrodes are connected by a wire, allowing the free flow of electrons, creating an electric current. However, without a salt bridge, the electrochemical reaction would soon grind to a halt. This is because the buildup of positive and negative ions in their respective half-cells would bring the process to a stop.

Electrical Neutrality

Electrical neutrality is vital for the continuous operation of an electrochemical cell. Without it, the electrochemical reactions would quickly become unbalanced. The main role of the salt bridge in an electrochemical cell is to maintain this electrical neutrality. As the reactions at the electrodes proceed, one half-cell accumulates excess positive charge, and the other accumulates excess negative charge.
To prevent this imbalance, a salt bridge containing a concentrated solution of inert salt enables the motion of ions between half-cells without participating in the electrode reactions. The ions in the salt bridge migrate to counteract the charge differences in each half-cell. This process restores the charge balance, ensuring the cell's ongoing operation.

Ion Mobility

Ion mobility within the salt bridge is an essential concept for maintaining electrical neutrality in an electrochemical cell. The choice of ions in the salt bridge is important—usually, ions that have similar mobility or speed of movement are selected. This ensures that the charge is balanced as ions move to opposite half-cells, responding to changes in charge distribution.
If the ions move at similar speeds, they effectively prevent the accumulation of charge on either side, maintaining the cell's functional operation. The nearly equal velocities of ions help create a stable environment that supports the ongoing electrochemical reactions, avoiding any disruptions due to uneven ion flow.

Circuit Completion

The function of a salt bridge extends beyond just maintaining electrical neutrality; it also plays a critical role in circuit completion. In an electrochemical cell, the external circuit consists of electron flow across a wire connecting the two electrodes. However, to have a fully closed circuit, an internal pathway for ion exchange between the two solutions is required.
The salt bridge provides this internal pathway, allowing ions to move freely between the half-cells, as they maintain balance. Without the salt bridge, the circuit would be incomplete, causing the electrochemical cell to cease functioning as the reactions would stop due to the rapid buildup of ionic charge.