The Nernst equation states:
For a concentration cell that has a potential of 0.089 V and utilizes Ni²⁺ solutions at the anode and the cathode, which of the following statements correctly describes the molar cell concentrations [Ni²⁺]_anode and [Ni²⁺]_cathode and the direction of electron flow within the cell?

Question

The Nernst equation states:

For a concentration cell that has a potential of 0.089 V and utilizes Ni²⁺ solutions at the anode and the cathode, which of the following statements correctly describes the molar cell concentrations [Ni²⁺]_anode and [Ni²⁺]_cathode and the direction of electron flow within the cell?

Quizplus · Accepted Answer

11ecba2d_11c6_5d9d_a3bf_1ba80dac35c0_MD0008_00 A concentration cell employs the same electrode material and ionic solution for both the cathode and the anode, but the ion solutions surrounding the anode and cathode differ in concentration. As a result, the same half-reaction occurs at both electrodes, but it occurs as an oxidation at one and as a reduction (in the reverse direction) at the other. Accordingly, adding the two half-reactions yields a result of E° = 0.00 V. The electrons will migrate from the cell with fewer cations to the cell with more cations until the cation concentration in each cell is equal. Because oxidation occurs at the anode, this is the source of electrons for the cell, which are transferred to the cathode where reduction occurs. Because the measured potential for the cell is positive (E = 0.089 V), the ion concentrations must have a ratio of [X]_anode/[Y]_cathode that is less than one so that the logarithmic term of the Nernst equation will be negative. A negative logarithmic value multiplied by the negative constant in the equation results in a positive value for E. Therefore, [Ni²⁺] is greater at the cathode, and the electrons in this cell will flow from the anode to the cathode. (Choices A and C) If [Ni²⁺] were greater at the anode, the ratio of [X]_anode/[Y]_cathode would be greater than one, and the logarithmic term of the Nernst equation would be positive, causing the final value of E to be negative. The positive value observed for E indicates that [Ni²⁺] is lower at the anode. The electrons will flow from the anode (fewer cations) to the cathode (more cations) to reach concentration equality. (Choice D) The relative concentrations are correct but the electrons will flow from the anode to the cathode, opposite to that stated. Educational objective: Concentration cells use the same electrode material and ionic solution at both the anode and the cathode but operate by a concentration difference between the cells, which produces a difference in potential. Electrons will migrate from the anode (fewer cations) to the cathode (more cations) until the concentrations equalize.

The Nernst Equation States