Mercury beating heart

Mercury drop pulsates when it is touched with an iron nail

Scientific name: Mercury surface tension changes in the mercury oxidation reaction

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Safety

Wear lab goggles and gloves. Mercury vapours are very toxic! This experiment must be performed in a fume hood.

Always follow general safety recommendations. Please note that conducting chemistry experiments you must comply with the relevant legal procedures in your country.

Reaction formula

2 Hg + SO42- → Hg2SO4 + 2 e-

Cr2O72- + 14 H+ + 2 e- → 2 Cr3+ + 7 H2O

Hg2SO4 + 2 e- → 2 Hg + SO42-

Fe → Fe2+ + 2 e-

Step-by-step instruction

  1. Carefully put a drop of mercury into a watch glass.
  2. Pour 6M sulfuric acid to just cover the mercury drop.
  3. Add small amount of potassium dichromate.
  4. Touch to mercury surface with an iron nail. The nail should be immersed in the sulfuric acid. The tip of the nail should just touch the mercury surface. The mercury drop begins to pulsate.

Scientific background

Pulsation of the mercury drop is due a change of the surface tension. In the acid solution mercury is oxidized, and surface tension decreases. Mercury drop contacts with iron nail, and iron reduces the mercury ions to mercury metal because it has a sufficiently negative electrochemical potential. Surface tension of mercury increases, and the drop shrinks. Thus the contact of mercury and iron is broken and this oscillation cycle repeats.

Danger:
Coolness:
Difficulty:

Published on 22 September 2015

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst