100 Days of Science #51-- Color Changing Iodine Experiments

I had purchased this tincture of Iodine off of Amazon to go along with an experiment in our science book. 

 However, when it came time to do the actual experiment the boys and I were not interested in it at all.  The experiment had to do with how our bodies break down food and called for chewing up pieces of food and spitting it back out on paper.... ugh! No thank you!

So I searched around Pinterest looking for a few experiments we could do using the iodine.  We found this fun one that dealt with color changes and chemical reactions and decided to give it a try.  

It was just perfect for a continuation on our chemistry unit! 

For the experiment we needed:
Clear cups
100 mg Vitamin C tablets 
Hydrogen Peroxide (3% household variety)
liquid starch
warm water
measuring spoons and cups

First we crushed up a vitamin c tablet until it was pretty fine. 

We added the vitamin c with 2 ounces of warm water until it was mostly dissolved.

We set aside cup #1 and turned to cup # 2.  In cup two we added 2 ounces warm water and 1 TEASPOON of our first solution.  The first time we tried the experiment we accidentally used 1 Tablespoon of the watered down vitamin c and our experiment failed.

Our third cup we mixed together 2 ounces warm water, 1 Tablespoon hydrogen peroxide, and 1/2 teaspoon of the liquid starch.

With our three cups all ready and mixed we set to work to watch the color changes.  First we mixed one teaspoon of iodine into our second mixture (the doubly watered down vitamin c).  We  barely had time to register the iodine going into the cup before it disappeared!

The iodine and the vitamin c molecules mix together and create Iodide which is colorless!

We then took this very same solution and added all of cup number 3 (the one with the peroxide and starch).  After mixing for a bit we had a deep purple solution.  It took quite awhile to see the color change and we actually thought the experiment had failed and we started over a second time.  We may have gotten a bit impatient and added more starch than was necessary...

Then boom like magic it turned a really dark purple! (You might get more of a blue color we added a bit more starch to our solution and so we ended up with a very dark purple).

The iodine is reacting with the starch which creates the dark blue/ purple color.  It takes so long for the color change to take place because the iodide has to be broken down.

If you add cup #1 (or more vitamin C) to the purple solution it will begin to turn clear again.  We could see how enough vitamin c would reabsorb the iodine and create another clear solution but none of the boys felt like crushing another tablet to turn it completely clear.

We had lots of fun with our magical color changing solutions.

Others in this series:
2.  Field Trip to the Ecotarium 
3.  Learning About Air Molecules
JENerally Informed


  1. I remember doing this in Science class growing up. I would love to show this to my girls.

    1. I had never seen this done before but it was really neat to see it just magically change color right before our eyes.

  2. What an interesting science experiment. I will have to try this with my grandsons--thanks!

  3. To add to this and learn about diffusion, put the starch mix in a Ziploc bag and the iodine in a bowl. Put bag in bowl and let it set a spell. See the colour change.

  4. Cool! my son did similar experiments recently with his biology co op class. Always amazing to SEE science right before your very eyes!


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