Make a clear liquid turn black in midair with this bizarre science experiment

This "iodine clock" experiment is so cool, we feel cheated that we never got to do it in high school chemistry lab.

But it turns out the popular experiment is so simple to do— involving only a bit of water, liquid iodine, potato starch, and a few other common reagents — that it can be done at home or even at work.

That is, if your bosses don't mind having their minds blown in the company kitchenette.

First, observe how magical this looks. In this IncredibleScience YouTube video, inky black liquid is poured into a cup, where it instantly turns clear:

The same chemistry can make the liquid clear one minute, then just go "poof!" into darkness the next.

This happens because different forms of iodine reflect light in different colors.

Iodine dissolved in a liquid becomes iodide (I^-) and is clear, for example, while gaseous iodine (I₂) looks purple.

When iodine and starch are dissolved together in water, gooey starch molecules instantly trap iodine ions close together to create a dark, blueish-black color. (Dripping liquid iodine onto a potato will turn it the same color, due to all of the spud's starch.)

But you can slow down or reverse the reaction by adding a bit of sulfite (SO₃) — common in most vinegar— which is used up at a very consistent rate. The moment it runs out, it's every iodide ion for itself; the starch immediately nabs the ions, complexes them, and goes dark.

The coolest part, though, is that increasing the concentration of sulfite can lengthen "clock," making science look more like magic in the hands of a practiced chemist.

Sir Martyn Poliakoff, a world-renowned chemist at the University of Nottingham, explains in more detail how the reaction works in this Periodic Videos clip.

Sir Poliakoff and his video crew show the set of reactions that use up the sulfite:

And they also recorded the reaction with a high-speed video camera, which reveals the moment the sulfite runs out in slow-motion:

To try this at home, you can buy a $10 kit that's made for doing this experiment from Incredible Science. The instructions are included.

Or, you can go the DIY route using materials found at the grocery store or pharmacy. Here's what you need, according to Curiosity.TV:

Materials

• liquid iodine
• potato flour
• water
• vinegar
• Vitamin C tablet
• hydrogen peroxide
• 3 glasses

Steps

1. Add 1 tsp. of potato flour to a glass of water.
2. Crush up the Vitamin C tablet and dissolve it in a second glass of water.
3. Add a few drops of iodine to the third glass of water. It should be organgeish-brown.
4. Add 2 tsp. of vinegar to the glass of iodine. It should still be brown.
5. Pour the Vitamin C glass into the iodine glass. It should turn clear!
6. Pour the potato flour glass into the iodine glass.
7. Finally, add about 4 tsp. of hydrogen peroxide to the iodine glass.
8. Wait about 1 minute. It should turn blueish-black!

You can play with adding the ingredients at different times and in varying concentrations to control when the solution changes color.

No matter what, you'll look like a magician — but you'll know it's just cool chemistry.

Here's the full video from Curiosity.TV showing how you can do the experiment using materials you could find at the store:

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