For the electrochemical cell Ag|AgCl|MCl(0.01 M)|MCl(0.02 M)|AgCl∣Ag, the junction potential is the highest when M⁺ is

Concept:

→ The electrochemical cell given has a reference electrode (Ag|AgCl) and a working electrode (Ag|AgCl|MCl(0.01 M)|MCl(0.02 M)|AgCl).

→ In order for the cell to function properly, an ion-conducting bridge or a salt bridge is used to connect the two compartments of the cell.

→ The junction potential arises due to the difference in the composition of the two electrolyte solutions on either side of the bridge.

→ The junction potential (E_j) can be calculated using the following equation:

E_j =\( \frac{RT}{zF}ln\frac{[M+2]}{[M+1]}\)

where R is the gas constant, T is the temperature, z is the charge on the ion, F is the Faraday constant, [M+2] is the concentration of the electrolyte solution on the electrode side of the bridge, and [M+1] is the concentration of the electrolyte solution on the reference electrode side of the bridge.

Explanation:

→ For the given electrochemical cell, we can see that the concentration of MCl on one side of the bridge is 0.01 M, while on the other side it is 0.02 M.

→  Therefore, the concentration of M+2 is higher on the electrode side of the bridge, and the concentration of M+1 is higher on the reference electrode side of the bridge.

→ Now, when M⁺ is H⁺, the charge on the ion is +1. Therefore, z = +1 in the above equation. Since the concentration of M+2 is higher on the electrode side of the bridge and the concentration of M+1 is higher on the reference electrode side of the bridge, ln([M+2]/[M+1]) will be positive.

Conclusion:
Thus, we can conclude that the junction potential will be highest when M⁺ is H⁺ in the given electrochemical cell.