The kids really enjoyed this simple experiment of using iodine to identify starch. I got to thinking about iodine after writing last week’s water post, because I remembered using iodine tablets to purify water when I went hiking on the Inca trail as a thirteen-year-old. It’s hard to visually explain that experiment, but the starch one is quite striking! I pulled out some iodine wipes (warning: iodine STAINS – be careful!), and we set up our experiment. Iodine in liquid form or tablet form can also be used; simply dissolve the tablets with a little bit of water for this experiment. I put flour, salt, and oatmeal on the plate, and then added baking powder on a whim, just to see what would happen.
Iodine and Starch Simple Experiment
Salt doesn’t have any starch, so the iodine stays brown.
Flour has a lot of starch! The iodine turned dark purple! We added a few drops of water with a syringe to help our drop of iodine to mix with the flour.
Oatmeal also has a lot of starch! It turned purple as well, although cooked oatmeal might have allowed the iodine to spread more thoroughly. Or a little more water =)
The baking soda bubbled up and turned purple at the edges. The purple is probably because most baking soda has some starch mixed in, but I’m still not sure why it bubbled. Does anyone know?
Update: It bubbles because baking powder contains baking soda – thanks to Carolyn Wilhelm and my IRL friend Kathy for reminding me of this! As Ann noted in her comment, baking soda reacts to acids, so the iodine must be slightly acidic. Here is Kathy’s explanation, if you would like the chemical details (thanks, Kathy!):
I think you created a chemical reaction with the Iodine (I2) baking soda NaHCO3 and water H20 to form a new chemical compound and also CO2 (gas) is a biproduct… which is what the bubbles would be… this is also what makes muffins, cookies, etc rise when baked is the release of the carbon dioxide gas…
The kids thought this was fascinating – and very strange! Johnny asked us to put it in the fridge for a while to see if that changed anything. It didn’t, but I was thrilled to see him taking our experiment one step further!