Question

Why is 1M of the electrode metal's metal salt added to half cells when measuring their standard potential? Wouldn't we still achieve a potential difference between the electrode and the electrolyte even without such an addition?

Answer 1

When measuring the standard potential of an electrode, the addition of a 1M metal salt solution to the half-cell serves a specific purpose. The primary reason for adding the metal salt solution is to maintain a constant concentration of metal ions in the solution, which helps establish a well-defined equilibrium state for the half-cell.

Here are a few key reasons why this addition is necessary:

1. Nernst Equation: The standard potential of an electrode is determined by the Nernst equation, which takes into account the activities or concentrations of reactants and products in the electrochemical cell. By adding a 1M metal salt solution, the concentration of metal ions remains relatively constant, which allows for accurate determination of the standard potential using the Nernst equation.

2. Equilibrium Condition: The addition of the metal salt solution helps establish an equilibrium state in the half-cell. This is important because the standard potential is measured under conditions where the half-cell is at equilibrium. By maintaining a constant concentration of metal ions, the electrode reaction can reach equilibrium, ensuring that the measured potential reflects the true standard potential.

3. Ion Conductivity: The metal salt solution enhances the ionic conductivity in the half-cell, allowing for efficient electron flow during the electrode reaction. This ensures that the measured potential accurately represents the electrode's behavior under equilibrium conditions.

Without the addition of a metal salt solution, the concentration of metal ions in the half-cell might vary over time due to electrochemical reactions or other processes, leading to an inconsistent potential measurement. Additionally, the 1M concentration is chosen because it provides a sufficiently high concentration to maintain a stable ionic environment without significantly affecting the thermodynamics of the half-cell reaction.

In summary, the addition of a 1M metal salt solution to the half-cell when measuring standard potential helps maintain a constant metal ion concentration, establishes an equilibrium state, and ensures accurate determination of the electrode's standard potential using the Nernst equation.