Beating mercury heart

The beating mercury heart (also: pulsating mercury heart ) is an oscillating electrochemical redox reaction between the elements mercury , iron and chromium or manganese . The reaction causes a drop of mercury to vibrate. The beating mercury heart in the shape we know today was first described by Friedlieb Ferdinand Runge in 1829.

experiment

For the experiment, a drop of mercury is placed in a watch glass and covered with an electrolyte such as sulfuric acid , which contains an oxidizing agent such as hydrogen peroxide , potassium permanganate or potassium dichromate . When the mercury drop touches the tip of an iron nail from the side, it begins to pulsate.

mechanism

When the mercury touches the nail, the less noble metal, iron, releases electrons. The mercury droplet becomes negatively charged. As the electrons repel each other, the droplet takes on a spherical shape. This means that contact with the iron is lost.

${\displaystyle \mathrm {Fe} \longrightarrow \mathrm {Fe} ^{2+}+2\ e^{-}}$

In the next step, the charged mercury droplet reduces the permanganate ions or dichromate ions present in the electrolyte solution according to:

${\displaystyle \mathrm {2\ MnO_{4}^{-}+16\ H_{3}O^{+}+10\ e^{-}\longrightarrow } }$ ${\displaystyle \mathrm {2\ Mn^{2+}+24\ H_{2}O} }$

or

${\displaystyle \mathrm {Cr_{2}O_{7}^{2-}+14\ H_{3}O^{+}+6\ e^{-}\longrightarrow } }$ ${\displaystyle \mathrm {2\ Cr^{3+}+21\ H_{2}O} }$

By reducing the permangate or dichromate, the mercury droplets emit electrons. This reduces the surface tension and the droplet comes into contact with the iron nail again. This causes the droplet to pulsate and act like a beating heart.

Although this response is mediated by changes in surface tension, other oscillatory responses, such as B. the Belousov-Zhabotinsky reaction , very similar.

literature

• HW Roesky : Chemical Cabinet Pieces : Spectacular experiments and witty quotations , 331 pages, Verlag Wiley-VCH Verlag GmbH & Co. KGaA, ISBN 3527294260 , ISBN 978-3527294268 .

Web links

• Beating Mercury Heart on YouTube , accessed February 8, 2019.
• Another video on the beating mercury heart with the kind permission of YouTube user xofunkox-scientific experiments on YouTube, accessed on February 10, 2019

Individual evidence

1. ↑ Hartwig Möllencamp, Bolko Flintjer, Walter Jansen: 200 years "Pulsating Mercury Heart " On the history and theory of a fascinating electrochemical experiment. In: CHEMKON. 1, 1994, pp. 117-125, doi : 10.1002 / ckon.19940010303 .