"Mercury beating heart" experiment
How to make a mercury drop pulsate
In this experiment, a mercury drop starts pulsating quickly from the touch of an iron nail.
Reagents and equipment:
- 6M of sulfuric acid;
- potassium bichromate;
- iron needle (nail).
Place a small drop of mercury carefully on a watch glass. Pour the 6M solution of sulfuric acid so that the mercury drop is completely covered with the liquid. Add a small amount of potassium bichromate. Carefully touch the surface of the mercury drop with an iron nail, needle or wire. The iron should be dipped in the sulfuric acid. The end of the iron object should barely touch the surface of the mercury drop. Observe the mercury drop start to pulsate.
The mercury drop pulsates as a result of a change in surface tension. In the acid which acts as an electrolyte, in the presence of the oxidizer potassium bichromate, the mercury on the surface of the drop oxidizes, which causes a reduction in surface tension compared with the unoxidized metal. When the mercury makes contact with the metal item, the iron reduces the mercury on the surface, as a sufficiently negative electrochemical potential arises between these metals. When it is reduced, the surface tension of the mercury drop increases, and the drop contracts. This causes contact between the mercury and the iron to break, the mercury is oxidized again, the surface tension decreases, and the drop spreads out once more. As a result, the drop touches the metal again, and the cycle repeats.
Mercury is a very toxic substance! Its fumes are poisonous! Don’t conduct the experiment at home! Make sure the acid does not come into contact with the skin, and don’t let the substances in the experiment near your eyes or mouth. Wear protective glasses and gloves. Follow general safety recommendations. Chemical experiments must be carried out in full compliance with the legislation of your country, more safe experiments for kids you can fing through our chemical sets for kids monthly subscription.
Warning! Substances of this experiment are toxic and highly dangerous for your health. Do not try this at home. Only under professional supervision.