Clock Reaction – Fun with Frederick and Fleming

Welcome to this week’s fun with Frederick and Fleming. Today we are going to do what is often referred to as a clock reaction. This reaction is one that has been done for hundreds if not thousands of years. Magicians or sorcerers would often use this “trick” to amaze people and also to try to fool people by saying that the color change determines if they are telling a lie or not.

Before the newscast, we mixed up two test tubes ahead of time. The first is corn starch and water with an unnamed chemical that delays the reaction. The other is iodine. Now normally you think of iodine as being dark, but that is only the case when the iodine is electrically neutral. Since in this case it is neutral, it is clear.

When we mix the two chemicals, the iodine reacts with the starch to become the black color. It doesn’t happen right away though as we also have a chemical that reverses the reaction. This back and forth happens about a thousand times a second until the chemical that switches it back gets used up and the iodine becomes neutrally charged and turns black/blue/purple.

When the iodine is again switched back to a negative charge, it becomes clear again and that can be seen when poured into the flask.

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