Uploaded March 2021 | Updated September 2026, 2 weeks ago
Chemists are so punctual – they’ve even designed a chemical clock!
Hydrogen peroxide is a very active compound and can be both an oxidizer and a reducing agent. In this process, it reduces iodic acid to form molecular iodine and a so-called triiodide complex. This process can be simplified to the following chemical reactions:
HIO₃ + 3H₂O₂ → HI + 3O₂↑ + 3H₂O
5HI + HIO₃ → 3I₂ + 3H₂O
HI + I₂ → H[I₃]
Since oxygen is formed during the first reaction, we can observe the emergence of the gas. The iodine and triiodide complex turn the solution amber. But the solution immediately turns blue, since the starch molecules, which are very long and look like spirals, trap iodine molecules like a fishnet, forming a deep blue iodine-starch complex. Under the action of malonic acid, this complex is destroyed, since it reduces iodine molecules, while the solution itself becomes colorless:
C₃H₄O₄ + I₂ → C₃H₃O₄I + HI
The process repeats every few seconds, and the reaction period depends on the concentrations of the initial solutions. What is this if not a chemical clock?
Fun and safe experiments await you in the MEL Chemistry subscription!
Attention! All experiments are performed by professionals. Do not attempt.
Chemists are so punctual – they’ve even designed a chemical clock!
Hydrogen peroxide is a very active compound and can be both an oxidizer and a reducing agent. In this process, it reduces iodic acid to form molecular iodine and a so-called triiodide complex. This process can be simplified to the following chemical reactions:
HIO₃ + 3H₂O₂ → HI + 3O₂↑ + 3H₂O
5HI + HIO₃ → 3I₂ + 3H₂O
HI + I₂ → H[I₃]
Since oxygen is formed during the first reaction, we can observe the emergence of the gas. The iodine and triiodide complex turn the solution amber. But the solution immediately turns blue, since the starch molecules, which are very long and look like spirals, trap iodine molecules like a fishnet, forming a deep blue iodine-starch complex. Under the action of malonic acid, this complex is destroyed, since it reduces iodine molecules, while the solution itself becomes colorless:
C₃H₄O₄ + I₂ → C₃H₃O₄I + HI
The process repeats every few seconds, and the reaction period depends on the concentrations of the initial solutions. What is this if not a chemical clock?
Fun and safe experiments await you in the MEL Chemistry subscription!
Attention! All experiments are performed by professionals. Do not attempt.
