“Mercury heart” experiment
How to make a mercury drop throb like a heart
Can you bring metal to life? In this experiment, you’ll see how one touch to a drop of mercury makes it throb like a heart.
Mercury is a very toxic substance, and its fumes are poisonous! Don’t conduct this experiment at home! Avoid exposing skin to acid and keep the substances in the experiment away from the eyes and mouth. Wear protective glasses and gloves. Follow general safety rules. Conducting chemical experiments should fully comply with the legislation of your country.
Warning! Don’t try to repeat this experiment without a professional supervision!
Reagents and equipment
- drop of mercury;
- 5mL diluted sulfuric acid;
- 5mL potassium dichromate solution;
- iron nail;
- Petri dish.
Carefully place a small drop of mercury in a Petri dish. Pour the sulfuric acid solution over it. Add a little potassium dichromate. Carefully touch the surface of the mercury drop with an iron nail, needle, or wire. The iron object should be in the sulfuric acid and barely touching the metal drop. The mercury drop will start to throb like a heart.
The throbbing is connected to a change in the surface tension of the drop. In the solution of potassium dichromate, the mercury oxidizes, and a film of mercury(I) sulfate Hg₂SO₄ forms on its surface. As a result, the surface tension of the mercury is reduced and the drop expands.
2Hg + SO₄²⁻ → Hg₂SO₄ + 2e⁻
Cr₂O₇²⁻ + 14H⁺ + 2e⁻ → 2Cr³⁺ + 7H₂O
When the iron nail touches the drop, an oxidation-reduction reaction occurs. The iron dissolves and the mercury(I) sulfate reduces to metallic mercury. As a result, the surface tension of the drop increases again, it contracts, and the contact with the iron is lost.
Hg₂SO₄ + 2e⁻ → 2Hg + SO₄²⁻
Fe → Fe²⁺ + 2e⁻
hen the surface of the mercury is oxidized again, the drop is once again covered with a layer of sulfate, it expands and touches the nail again. The process repeats, and the drop throbs like a heart!