🧪 Science with Sarah: Iodine & starch tincture ⚗️

This color-changing experiment is a great example of chemistry

👉 Watch the video of Sarah’s school science experiment here!

Hello parents, teachers and students! If you’re looking for fun way to explore chemistry with you middle-school aged kiddos, this experiment is for you!

Be sure to check out GMSA@9 on Wednesdays when Meteorologist Sarah Spivey does the demonstrations and explains the science behind it.

Science with Sarah: Invite KSAT to your school for live science experiments. (KSAT)

HERE’S WHAT YOU’LL NEED

Iodine/Starch experiment materials. (Copyright KSAT 2023 - All rights reserved)
  • Eye protection
  • Apron (Optional)
  • Gloves (Optional)
  • Aluminum foil
  • 2 clear plastic cups
  • Water
  • Cornstarch
  • A spoon
  • Pipettes (Amazon link)
  • Iodine (Amazon link)
  • Potatoes (sliced), Bread slices, bananas (sliced), lettuce, apples (sliced)

DO THE EXPERIMENT

  • STEP 1: Wear eye protection! You don’t want to get iodine splashed in your eyes. Also, iodine can stain, so wear an apron or gloves if you want to avoid stains
  • STEP 2: Lay out some aluminum foil as your workplace
  • STEP 3: Fill the two cups about 3/4 full of water
  • STEP 4: Using the spoon, add a scoop of cornstarch to one of the cups and stir.
  • STEP 5: Take a pipette’s worth of iodine and put it in the cup of water without the cornstarch. Notice that the iodine turns the water a pale yellow color.
  • STEP 6: Take a pipette of iodine and squeeze it into the cup with cornstarch. The water should turn a deep purple, blackish color as the iodine reacts to the starch. See picture below
Two cups contain iodine, only one contains starch (Copyright KSAT 2023 - All rights reserved)
  • STEP 7: Now, test the various food items for starch by placing a few drops of iodine on each food item. If the food contains starch, the drops of iodine should turn a very dark color.

HOW IT WORKS

This experiment explores the chemistry of electrically charged iodine molecules. In the first-aid mixture of iodine, like the one used for the experiment, the iodine breaks down electrically when introduced to starch.

We see the deep purple color as a result of the higher energy level emitted by the iodine-starch mixture. See the example of iodine on starchy bread below.

Iodine on bread (Copyright KSAT 2023 - All rights reserved)

SCIENCE WITH SARAH

If you’d like Sarah and David to come to your school and conduct a science experiment live on KSAT, email sciencewithsarah@ksat.com.

Parents and guardians: upload a video of your child performing the activity by clicking here. Send it in and you might see it on GMSA @ 9 a.m.!


About the Authors:

Sarah Spivey is a San Antonio native who grew up watching KSAT. She has been a proud member of the KSAT Weather Authority Team since 2017. Sarah is a Clark High School and Texas A&M University graduate. She previously worked at KTEN News. When Sarah is not busy forecasting, she enjoys hanging out with her husband and cat, and playing music.

Ben Spicer is a digital journalist who works the early morning shift for KSAT.