The bizarre oscillating redox reaction between mercury and iron

Redox chemistry, electrode potentials and electrochemical cells are interesting, but can be hard work for sixth form students to understand. This fascinating little demonstration, whilst not the easiest to explain, will always impress your audience.

When an iron nail is placed close the mercury oscillates, 'beats', as if it has a life of its own and you will observe considerable movement or 'beating' if the oscillations are similar to the natural resonant frequency of the droplet. Look more closely and bubbles of gas, relatively rapid oxidation of the nail and fluctuating surface layers of mercury compounds can be seen.