Flag in a test tube

The two-layer liquid divides into three layers and changes its color.

Scientific name: Potassium dichromate reacts with hydrogen peroxide on the border of two immiscible liquids.

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Safety

Wear eye protection goggles and gloves. This is a violent reaction. Be very careful.

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

Reaction formula

K2Cr2O7 + H2SO4 + H2O2 → 2CrO5 + K2SO4 + 5H2O

2CrO5 + 7H2O2 + 3H2SO4 → Cr2(SO4)3 + 10H2O + 7O2

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. Fill one third of the test tube or breaker with potassium dichromate solution.
  2. Add some sulfuric acid to the potassium dichromate solution.
  3. Pour some diethyl ether on the top of the mixture. If you have added it carefully it should float on the top of the mixture since it is immiscible with water.
  4. Finally put a few drops of hydrogen peroxide to the vessel.
  5. A violent reaction between the components takes place. The organic layer turns blue. The appearance of the third dark layer on a border between organic and inorganic phases is observed. A large amount of gas is released.

Scientific background

In this experiment a two-layer liquid divides into three layers and changes its color because of the chemical reaction between the components. At the beginning of the experiment one has two immiscible layers. The first one is the water solution of potassium dichromate (K2Cr2O7) on the bottom of the test tube. The second one is diethyl ether. It is immiscible with water and floats on the top. When hydrogen peroxide (H2O2) is added to the test tube, it reacts with potassium dichromate as follows:

K2Cr2O7 + H2SO4 + H2O2 → 2CrO5 + K2SO4 + 5H2O

Chromium(VI) peroxide(CrO5) is soluble in diethyl ether and turns the organic phase blue. It is also a very unstable substance and reacts again giving the middle dark layer.

2CrO5 + 7H2O2 + 3H2SO4 → Cr2(SO4)3 + 10H2O + 7O2

A large amount of oxygen is released in this reaction. It rapidly comes up to the top of the vessel. In a breaker or test tube mixing conditions are not very good, so one can observe the front of the reaction proceeding.

Danger:
Coolness:
Difficulty:

Published on 04 March 2015

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