Ozone - preparation and detection

The violent release of ozone and darkening of iodine-starch paper

Scientific name: The disproportionation of oxygen from barium peroxide


Получение озона и его определение

by ФизматФильм


Wear eye protection goggles. Ozone is a poisonous gas! Work outdoors or in a 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

3 BaO2 + 3 H2SO4 → O3 + 3 BaSO4 + 3 H2O

2 KI + O3 + H2O → I2 + 2 KOH + O2

I2 + starch → I2*starch

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. Pour a few milliliters of concentrated sulfuric acid into a beaker.
  2. Place the beaker in a bowl with ice.
  3. While the sulfuric acid cools, prepare iodine-starch paper. For this, mix the solution of potassium iodide and the solution of starch. Moisten filter paper with the resulting solution.
  4. Add 1 spatula with barium peroxide in the cooled concentrated sulfuric acid.
  5. Observe the violent smoke emission. Insert the iodine-starch paper into the smoke. Observe its darkening.

Scientific background

Barium peroxide contains oxygen in an unusual oxidation state which is capable of disproportionate and leads to the formation of ozone. By itself, ozone is unstable, so the reaction should be performed at a low temperature.

Ozone is a strong oxidant which is capable of oxidizing the iodide-anions to free iodine. Reacting with starch iodine forms an iodine-starch associate which has a blue color.


Published on 30 June 2015

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