B16 Beating Heart

Description
This demonstration illustrates the changes in the characteristics of an electrode as a reaction occurs. Iron is oxidized and electrons are transferred to the mercury drop. The mercury drop distorts to maximize the distance between the electrons. A drop of dichromate at the other side of the mercury reacts with the electrons causing the drop to flatten again and come in contact with the iron nail. Several modes of vibration are shown in this sequence.

Equation
Cr₂O₇²^-(yellow) + 14 H⁺ + 6 e^- --> 2 Cr³⁺(blue) + 7 H₂O

Fe --> Fe³⁺+ 3e^-

Reference
L. R. Summerlin and J. L. Ealy,Jr.,"Chemical Demonstrations A Sourcebook for Teachers", American Chemical Society, Washington, DC, (1985) p. 93.