Chemistry 221

INSTRUMENTAL ANALYSIS
Problem Set #2: Electrochemistry

Problems in Skoog, Holler and Nieman

Additional Problems

It is said that many polarograms can be run on a single solution without causing significant depletion of the analyte. Consider an experiment in which the limiting current is monitored for 30 minutes in 50 mL of a 0.50 mM Cd²⁺ sample. What fraction of the Cd²⁺ is electrolyzed if the average current during the period is 4.0 microampere?
A DC polarogram of an organic compound had a limiting current of 5.00 microamperes. The following data were obtained from the rising portion of the wave:
- -0.475 volts --> 0.62 microamps
- -0.490 volts --> 1.57 microamps
- -0.510 volts --> 3.43 microamps
- -0.525 volts --> 4.38 microamps
From these data, describe how you would determine whether the reduction is electrochemically-reversible and, if reversible, how you would determine n and E_1/2. For the overachievers in the class: determine whether the reduction is reversible and, if it is reversible, determine n and E_1/2.