Aluminum Metal Digestion as a Demonstration of an Oscillating Voltage Reaction: An Application Beyond the Textbook

Abstract

The oscillating open-circuit voltage generated by the digestion of aluminum rods, catalyzed by copper(II) chloride in 3 M nitric acid at 90 °C, is presented as a demonstration appropriate for a general chemistry or advanced laboratory. This demonstration encourages discussion of the possible kinetic mechanism as well as the general electrochemical halfreactions involved and the limited conditions under which oscillations occur. The objective is to provide general chemistry students with an interesting reaction beyond typical kinetics or electrochemistry. Apart from 1100-alloy aluminum rods and a recording voltmeter, the demonstration uses standard lab equipment, and the materials for the solutions are those typically found in a general lab setting.

A Simple Chemical Oscillator: The “Educator”

“…Teachers, students, and observers of chemistry are captivated by oscillating chemical reactions. Consequently, it is no wonder that reports on chemical oscillators are found in the chemical education literature in every decade since the 1970s. − Such reports have described experimental setups, − computer modeling, − and theoretical discussions − of oscillating reactions. While these reactions are fascinating, an understanding of how such systems operate can be difficult to achieve.…”

“…Oscillations in potential and current have been observed on a variety of metal electrodes immersed in electrolyte or acidic solutions. ,− For example, oscillations in current have been observed on iron electrodes placed in solutions of sulfuric acid (Figure , for example) …”