Lie Detection with the Classic Iodine Clock Reaction

Clay and Nick from Lenski Elementary joined me on 9News this week to test the honesty of 9News anchor Mark Koebrich.

Two clear liquids are mixed together and a question is asked. A truthful answer, and the liquid will remain clear. An untruthful answer will cause the liquid to change color. Mr. Koebrich told a lie, and BAM! the liquid turned to black ink.

Okay, maybe a lie detector is going a little too far. It’s really a chemical reaction that is causing the clear liquid to change to black. The Iodine Clock Reaction is one of the most startling chemical demonstrations you’ll ever see.

This reaction is referred to as the Landolt Clock Reaction. There are three steps in the process that cause this amazing reaction. When you prepare the Solutions A, B, and C, the chemicals begin to mix and form new chemical compounds. This is a very slow reaction, so you don’t see any outward changes. When you begin to pour the solutions together a much faster reaction occurs, which leads to the third reaction which is instant. Suddenly, and immeasurably quickly, the clear liquids turn into a jet black iodine-starch complex. These reactions happen at different intervals because different chemicals react at different speeds.

For more on this experiment, read the Clock Reaction experiment. For a kid-friendly all-in-one kit, check out our Think Ink Kit.