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Think Ink

From colorless to black and back again, this twist on the classic clock reaction is a must-do for any science enthusiast.

Two clear liquids are mixed together and the audience is told to watch closely… “Don't take your eyes off the liquid or you'll miss it!” Then, in a flash, the clear water changes to ink (or so they think!). Think Ink! illustrates the amazing chemistry behind the classic clock reaction where molecules meet up and change over time to create this startling effect.

Experiment Materials

Experiment

  1. Fill each test tube half-full with water.
  2. Tear a styrofoam pellet in half and place one-half into the first test tube. Tighten the lid and shake it up until the pellet fully dissolves.
  3. Place two level scoops of Timing Mixture into the first test tube. Use one mixing straw to stir it up.
  4. Add one level scoop of Trigger Powder into the second test tube. Use the second mixing straw to stir this test tube until the powder is completely dissolved.
  5. Mix the two test tubes together, back and forth, until the solution turns black.
  6. Add 1/4-scoop of recycling powder to the empty test tube. MIx the solution with the Recycling Powder and observe the instant reaction.

How Does it Work?

The Think Ink! reaction is based on the fact that iodine and starch molecules present in solutions A and B can combine to form a dark, blue-black color. But wait – why does it take 10-20 seconds for this to suddenly happen? Well, to understand how the Think Ink! reaction works we need to talk about a little chemistry.

Iodine has two different “oxidation states” – one where the iodine molecules have a negative charge (I-) and the other where they have no electric charge (I0) Only the iodine with no electric charge can combine with starch to make the blue-black color. Certain chemical reactions (called oxidation and reduction reactions) can make iodine shift back and forth between these two states…

When Solutions A and B are first mixed, all the iodine has a negative charge, and two separate reactions begin. Reaction #1 (oxidation) changes all of the I- to I0, but Reaction #2 (reduction) is faster and changes the I0 right back to I- again, so it has no chance to combine with the starch. The iodine zooms back and forth between these two states thousands of times a second (of course you can’t see this) until all of a sudden the chemicals that make Reaction #2 happen are all used up. Then it’s time for Reaction #1 to change all of the I- to I0 one last time, it combines with the starch, and – you have “INK!”