Knowledgebase

Background:

This experiment introduces the student to electrochemical cells. An H-cell is used with a Zn/Zn²⁺ (aq) half-cell on the right side as a reference. The student can deliver four different solutions into the left half-cell, which contains a Pt electrode. The voltmeter records the potential difference and also the temperature of the cell. For each solution, the student records a series of readings, averaging the fluctuations in voltage and temperature due to noise. In two cases, the solution's composition is known, so the student can calculate the reduction potential of the half-cell and compare it with a literature value. In one case, the composition is due to one of several possible unknowns assigned randomly, and the student must identify the ion. In the fourth case, the identity of the ion is known, but the concentration must be calculated using the Nernst Equation. Activity considerations are not discussed in this experiment.

Learning Objectives:

1. Study the design and function of an electrochemical cell.
2. Be able to perform a series of measurements, averaging noise fluctuations, and determine half-cell reduction potentials.
3. Be able to identify an unknown ion from its measured reduction potential using literature values.
4. Be able to calculate the concentration of an ion from its measured half-reaction potential at a given temperature using the Nernst Equation.
5. Be able to answer questions involving possible sources of error.