Vitamin C Lab – Color Change

homeschool science vitamin c lab experiment

This is a fun homeschool science lab to do with plenty of wow factor. In it, two colorless solutions are combined, and after a few minutes, there’s a vibrant color change.
The best part is that all of the materials from this lab can be easily found at your local grocery store or pharmacy. Even better, the homeschool science lab can be scaled up to make it more of a challenge for older kids. See notes below if you want to scale this lab up for higher grades.

In this experiment, two colorless odorless liquids are combined in different amounts to create a chemical change. It is a fairly safe lab and young, well-supervised kids can be left on their own to play around with the materials.

You’ll be using tincture of iodine. Iodine is poisonous, so kids should be reminded of the basic chemistry lab rules:
1. Do not eat or drink any materials.
2. Wear safety protection including goggles.
3. Waft with your hands to smell, don’t just stick your nose into the cup to smell.
4. No playing around!

For a more in-depth list of chemistry safety rules, check here.

Safety: Goggles are a must, long hair should be tied up, and while the materials are non-staining, lab coats are always a good idea.

Materials:

Sharpie or another permanent marker
Water
4 small plastic cups
Measuring cups and spoons from your chemistry supply kit
1000 mg Vitamin C tablets, or two 500 mg tablets (uncoated work best)
Tincture of iodine
Hydrogen peroxide 3%
Liquid laundry starch (you can use cornstarch in a pinch but the reaction will happen more slowly and will be less dramatic because the liquid will be cloudy)
Mortar and pestle (or something to grind the Vitamin C tablet)

Procedure:

  1. Use the mortar and pestle to crush a 1000 mg vitamin C tablet and dissolve it in about 60 mL (1/4 cup) of warm water. Stir for about 30 seconds and then let it sit to become more clear.
  2. Lable this cup “vitamin C solution”. Don’t worry if it is still a bit cloudy.
  3. Put 5 mL (1 tsp) of the vitamin C solution into a clean cup. Add 5 mL tincture of iodine and swirl to combine. Ask the kids to make observations.
  4. Lable this combination “liquid A”.
  5. In a third cup, combine 15 mL (1 tbsp) of hydrogen peroxide, 60 mL of water, and 10 mL (2 tsp) of liquid starch. Swirl gently to combine.
  6. Lable this cup “liquid B”.
  7. Now on to the fun part. Slowly pour ALL of the contents of the cup labeled “liquid A” into the cup marked “liquid B”. Slowly pour the liquids back into the liquid A cup, repeating this process a few times (2-3 times should do it), then set the cup down and observe.
  8. After a few seconds, the liquid should turn suddenly blue!

The Science:

Color change is evidence of a chemical change, but in this homeschool science experiment, there are actually two different chemical reactions going on when you combine the solutions. First, you should know that there are two forms of iodine created in this reaction: iodine, and the ion form of it, iodide.

Iodide (ion) + Starch —————-> Colorless

Iodine (element) + Starch ———-> Dark Blue

It is the iodide ions inside the tincture of iodine that react with hydrogen peroxide, producing the iodine element which turns blue in the presence of starch.

However, the vitamin C reacts with the iodine preventing the solution from turning blue. That is, until, all the vitamin C is used up during the reaction. Once that happens, it no longer breaks apart the new iodine molecules being created, so the solution turns blue.

This is a classic chemistry reaction called the Iodine Clock Reaction. And, it’s a nifty way to get the kids to play with different variables. they can add less water (adding fewer molecules to get in the way of iodide and hydrogen peroxide reaction forming iodine) allowing for a faster reaction, or they can adjust the amount of vitamin C, starch, and even hydrogen peroxide to try to speed up the reaction.

Further Exploration:

Ask your kids if the temperature of the water changes the speed at which the reaction changes color? Try it!
Would a different amount of the vitamin C solution affect the reaction? Try it!
Does stirring more or less vigorously change the time it takes the liquids to try?

Notes:

To see this reaction in action, this Wiki page has a brief video and plenty more about the science behind this homeschool science experiment.

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