Question

The function of a salt bridge is to : (a) maintain electrical neutrality of both half cells (b) increase the cell potential at the positive electrode (c) decrease the cell potential at the negative electrode (d) eliminate the impurities present in the electrolyte

Short answer

The function of a salt bridge is to maintain electrical neutrality of both half cells (Option a).

Step-by-step solution

Understanding a Salt Bridge

A salt bridge is a component in an electrochemical cell that connects the oxidation and reduction half-cells and maintains the electrical neutrality by allowing the flow of ions.

Option Analysis - A

Option (a) states that a salt bridge maintains electrical neutrality of both half cells, which is accurate because it completes the circuit by allowing ions to flow and balance charge changes in the half-cells.

Option Analysis - B

Option (b) suggests that a salt bridge increases the cell potential at the positive electrode. This is not the function of the salt bridge; it doesn't directly affect the electrode potentials but rather allows the cell to function properly by balancing charges.

Option Analysis - C

Option (c) is incorrect because the salt bridge does not decrease cell potential at the negative electrode. Its role is to maintain charge balance, not to change the potentials of electrodes.

Option Analysis - D

Option (d) is incorrect as the purpose of a salt bridge is not to eliminate impurities present in the electrolyte but to balance the ionic charges during the redox reaction.

Selecting the Correct Option

By analyzing the functions of a salt bridge, it is evident that the correct option is (a) which describes its key role in maintaining electrical neutrality of the half-cells in an electrochemical cell.

Key concepts

Electrochemical Cell

An electrochemical cell is a device capable of generating electrical energy through chemical reactions or facilitating chemical reactions through the introduction of electrical energy. These cells consist of two half-cells, each with its own electrode and electrolyte. The electrodes, typically made of different metals, are where redox reactions occur.

Electrochemical cells function through the movement of electrons from the anode to the cathode. This is usually set up in a way that the oxidation reaction, losing electrons, occurs at the anode, while the reduction reaction, gaining electrons, happens at the cathode. A wire connecting the two electrodes allows the electrons to flow, creating an electrical current. To maintain the flow and prevent charge buildup, a salt bridge is often used to balance the ionic charge between the two half-cells.

Understanding the design and function of an electrochemical cell is essential for comprehending how batteries work, how electrolysis is conducted, and the principles behind corrosion and electroplating.

Electrical Neutrality

The principle of electrical neutrality dictates that in an electrochemical cell, the total charge in each half-cell must remain balanced. This balance is crucial for the ongoing flow of electrons and the continuation of the redox reactions. As electrons move through the external circuit from the anode to the cathode during the cell operation, positive and negative ions are produced at each electrode. If not balanced, this would lead to a charge imbalance, which would eventually stop the flow of electrons.

To maintain electrical neutrality, a component known as a salt bridge is essential. The salt bridge contains a salt solution, which allows ions to flow between the two half-cells, neutralizing the charge buildup. Without the salt bridge or a similar mechanism, the electrochemical cell would quickly cease to function due to the interruption in the flow of electricity caused by an imbalance of charge.

Redox Reaction

A redox reaction is a chemical process involving the transfer of electrons between two substances. It consists of two half-reactions: oxidation, where a substance loses electrons, and reduction, where another substance gains electrons. This electron transfer is what enables an electrochemical cell to produce electricity. In the context of a cell, the substance that loses electrons at the anode is oxidized, while the substance that gains electrons at the cathode is reduced.

The balance of these two processes is fundamental to maintaining a steady flow of electrons. The salt bridge plays a critical role in ensuring that the redox reactions continue to occur by allowing ions to flow and by maintaining the concentration of electrolytes, preventing the cell from becoming polarized and disrupting the redox processes.

Electrode Potential

The electrode potential is the ability of an electrode to drive an electrical current through a circuit. It's measured in volts and depends on the metal's propensity to lose or gain electrons—the greater the tendency, the higher the potential. Each half-cell in an electrochemical cell has its own electrode potential. When connected, the difference between their potentials gives rise to the cell potential.

The electrode potential is affected by several factors, including the type of metal, concentration of ions in the electrolyte, and temperature. The role of the salt bridge is not to alter these potentials directly but to ensure that the conditions necessary for the redox reactions to proceed effectively are maintained, thereby influencing the overall cell potential indirectly by avoiding the interruption of current flow due to charge accumulation.