Orange tornado

The vortex formed under stirring is coloured in bright orange.

Scientific name: Mercury(II) iodide dissolves in excess of iodide ions.


Orange tornado

by ChemToddler

orange tornado

by thejackjones1


Wear goggles and disposable gloves. Due to toxicity of mercury(II) salts this experiment is hazardous.

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

Reaction formula

HgCl2 + NaI = HgI2 (orange precipitate) + 2NaCl HgI2 + 2NaI = Na2(HI4)

Step-by-step instruction

WARNING! This experiment is dangerous! You should NOT perform this at home. ONLY carry out this experiment, if you are a trained chemist, and you understand local safety and legal requirements, which are required to perform such experiments

  1. Prepare solutions of NaI and HgCl2.
  2. Put the flask with the solution of NaJ on a magnetic stirrer.
  3. Stir it to form a vortex.
  4. Add a small amount (about 1-2 ml) of HgCl2 to the central part of the vortex. The orange tornado will be observed.

Scientific background

When HgCl2 is added to the NaI solution a reaction between the components takes place: HgCl2 + NaI = HhI2 (precipitate) + 2NaCl HgI2 is highly insoluble in water. Yellow-orange particles of the precipitate formed during reaction color the solution. In the vortex the HgI2 concentration is higher than in other parts of the solution. At a distance from the central part of the flask it reacts with the excess of NaI as follows: HgI2 + 2NaI = Na 2(HI4) The product of this reaction is colorless and soluble. The equilibrium between soluble and insoluble products of the reactions is the reason why on a macroscopic level something resembling a tornado is observed.


Published on 28 January 2015

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