How To: Make an Iodine Clock Reaction at Home

In this video, I'll be demonstrating how anyone can make their own iodine clock reaction with simple over-the-counter chemicals.

Household Materials Needed

• Hydrochloric acid (for cleaning purposes)
• Hydrogen peroxide (3%)
• Sodium hydroxide (drain cleaner)
• Povidone-iodine (antiseptic)
• Cornstarch
• Sodium thiosulphate (used as water conditioner for fish bowls, but I got mine from a children's chemistry game)

The Reactions

In the first, slow reaction seen in the video above, triiodide ion is produced:

• H2O2 + 3 I- + 2 H+ -> I3- + 2 H2O

In the second, fast reaction, triiodide is reconverted to iodide by the thiosulfate:

• I3- + 2 S2O32- -> 3 I- + S4O62-

The color of the solution after the reaction is a result of the complex formed between iodine and starch that has dark blue color.