Testing for Vitamin C with Iodine – Free Lesson Printables

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In this experiment, we will be testing for vitamin C with iodine. We have conducted this test several times, repeated some liquids, and added new ones with each test.

Some of the juices we used included fresh lemon juice, Emergen-C® vitamin drink mix, store-bought orange juice, homemade pumpkin, acorn squash, and cranberry “juices” in our experiments.testing for vitamin c with idodine

Does pumpkin contain Vitamin C?  Let’s find out!

Note: A wide range of ages can complete this activity. We have added more advanced vocabulary and concepts for older students. The process and chemical reactions are interesting for all ages.

As you test for vitamin C, use the worksheets we have prepared as they apply to your children and their comprehension level. In other words, please don’t NOT do this experiment because of the more advanced explanations used in this intro and the “what happened” section of this post.

Why Test for Vitamin C with Iodine?

Vitamin C is ascorbic acid. A molecule of ascorbic acid is depicted below. Understanding how vitamins, proteins, and other important organic compounds are vital to our bodies will help our children make wise, health-conscious decisions. If you are doing a human body, nutrition, health, or animal science study, this experiment will relate well to any discussions on vitamins, minerals, and dietary choices.

Testing for vitamin c with iodine vitamin c molecule Ascorbic Acid Molecule

What are Vitamins?

Vitamins are small organic compounds that all living organisms need to survive – even microbes. Vitamins are typically broken into two categories: fat-soluble and water-soluble. These classifications can tell us a lot about the chemical composition of these vitamins (such as whether they are polar or nonpolar), along with indicating how quickly the vitamins are used in the body. Fat-soluble vitamins (A, D, E, and K) are stored in the fat of organisms to last longer, and the body releases them as needed. Water soluble vitamins (C and all B-complex vitamins) are quickly used in the body and released with the passing of urine.

But what makes Vitamin C so important?

While humans have robust systems capable of generating many nutrients and vitamins, we cannot create ascorbic acid for our own use, so we must take vitamin C supplements or ingest vitamin C through food and drink.

Testing for vitamin C with iodine photo of cells

In the human body, vitamin C is important for the repair of tissues, strengthening of bones, immune system support, and the absorption of iron by the body. Vitamin C acts as an antioxidant, which aids in the prevention of cancer by neutralizing free radicals.

What are free radicals?

Atoms have three main components: protons, electrons, and neutrons. The protons and neutrons make up the nucleus of the atom. The electrons orbit around the nucleus in what is called energy shells. Each energy shell has a certain number of electrons it needs to be full. The first shell can only hold 2 electrons, and each subsequent shell can hold up to 8. The number of electrons naturally found in each atom is called their valence electrons. For example, the first shell of carbon is complete with 2 electrons. Carbon only has four electrons in its secondary shell. This means carbon has a valence of 4 and can make four bonds with other atoms.

Free radicals are atoms, ions, or molecules that have become unstable due to having one or more unpaired valence electrons in their outer energy shell. Because of their unstable nature, they will begin to try and bond with stable electrons, which in turn causes them to become unstable. The instability causes a cascade of adverse effects. At the end of this post, we link to resources explaining the effects of free radicals on our bodies.

How do antioxidants help fight free radicals?

Antioxidants, like vitamin C, have an extra electron. As such, they are able to bond to those free radicals, causing them to become stable once again. Sometimes, antioxidants will completely undo the free radical molecules.

However, having too many antioxidants can be detrimental. If you are curious about the science behind this, follow the links at the end of this post.

In this activity, your student will use a laboratory technique called titration. When performing a titration, students will carefully add one drop at a time of one solution into another solution, stir, and observe for a color change. The drops required to reach the color change are recorded.

We are going to use a starch-iodine solution as our indicator. We will then add our different juices, one drop at a time, and observe the color change.

In our experiment, we will add juice drops into the starch-iodine indicator until the mixture is colorless.

There is highly accurate testing equipment in professional labs. But, we will go through the process as accurately as possible in our home laboratories!

Important: Iodine use comes with safety warnings. You can read and share this with your student. Here is a lab safety sheet on iodine. Please have safety glasses and gloves available before your children start testing for vitamin C with iodine.

Note: We did this experiment twice. The first time we tested for vitamin C, we used EmergenC®, fresh lemon juice, acorn squash “juice,” and cranberry “juice.” The second time we used pumpkin “juice”, fresh-squeezed lemon juice, and EmergenC®.

Preparing to do Some Testing for Vitamin C with Iodine

We talked about the experiment ahead of time and discussed what liquids we wanted to test. We selected Emergen-C®

, freshly-squeezed lemon juice (as opposed to bottled lemon juice), acorn squash juice, pumpkin juice, and cranberry juice.

Discuss with your children what liquids they want to test for vitamin C. Then, have them research the amount of vitamin C in a juice sample. Use the data sheet in our printable packet created for this experiment.

Download the free printable for this experiment. You will be added to our email community. We promise not to spam you! If the box below does not allow you to type in the boxes, please check for pop-up blockers on your browser. Also, do not include empty spaces at the beginning and end.

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As you proceed through the experiment, your children can then fill in the remainder of the data sheet and compare the results with the amount of vitamin C in a serving of the juice.

Testing for Vitamin C with Iodine – Step 1: Making “Juice”

Since we were testing liquids, we had to make our juice for the acorn squash, fresh cranberries, and fresh pumpkin. It’s important to note that you do not want to prepare the vitamin C samples too far in advance (as in several hours) as ascorbic acid can oxidize over time, given the exposure to oxygen in the air around us.

Testing for vitamin c with iodine supplies

To do this we:

  1. Cut up the pumpkin and ground it until we had about ½ cup of chopped pumpkin. We did the same for the acorn squash and the cranberries. The pulp from each was in its bowl.

Testing for Vitamin C with Iodine Extracting Juice from a Pumpkin

  1. To each bowl of ground-up material, we added 1/2 cup of distilled water. If we didn’t have some water at the bottom of the bowl, we added ¼ cup more. Stir each mixture well.
  2. Set aside for about 15 minutes.
  3. Use either coffee filters or cheesecloth to strain each mixture. Strain each juice into its flask or bowl. Be sure to keep everything separate. Use separate pieces of cheesecloth or coffee filters. If stirring or scraping a mixture out of a bowl, use different utensils between mixtures.

  1. You will end up with multiple containers of juice. It may be helpful to label each, if some of the liquids have a very similar color.

testing vitamin c with iodine - liquids to test

Testing for Vitamin C with Iodine – Making the Starch-Iodine Indicator

 For this portion of the experiment, you will need:

  • Distilled water
  • Measuring cup or beaker
  • Glass stir sticks or several clean spoons for stirring
  • Cornstarch
  • The liquids you are testing
  • Distilled water
  • Saucepan
  • Heat source
  • Test tubes and test tube rack. You could do this using glass bowls or beakers too. Adapt for what you have. Since we do chemistry activities with young children too, we use these plastic test tubes, but measure into these in this experiment using glass lab beakers for better accuracy.


  • Put on safety glasses and gloves. Iodine use comes with safety warnings. You can read and share this with your student. Here is a lab safety sheet on iodine.
  • In a glass container that will hold 12 ounces, add 2 tablespoons of cornstarch with just enough distilled water to make a paste. (If you have to add more water and cornstarch to get the paste eventually, that’s ok. We had to do that too.)

  • Measure 8 ounces or 250 mL of distilled water and mix it into the cornstarch paste.

testing for vitamin c mix cornstarch and distilled water

  • Stir well, then pour into a pan and bring to a boil. Stir constantly.
  • While waiting for the indicator to boil, have another person set up the test tubes or mixing containers you plan to use. Set up the liquids/juices you’ll be testing. Have the glass stir sticks or spoons ready too. If you have test tubes but don’t have the glass stirrers, you can swirl the test tube after each addition of drops.

testing for vitamin c with iodine set up test tubes

  • When the starch and water mixture reaches boiling, remove it from the heat.
  • Next, pour 4 ounces of this indicator solution into a glass bowl, flask, or measuring cup. (Be careful because it’s still very hot!)
  • Add enough drops of the iodine to turn the 4 ounces of indicator a dark blue, almost black. Stir well. This solution is the final starch and iodine indicator.

Testing for Vitamin C with Iodine – The Big Test!

Here are the procedures for testing for the presence of vitamin C with iodine:

You will need:

  • Pipettes or droppers – 1 for each liquid you are testing
  • Test tubes and rack or small glass bowls
  • Pencil and our handy recording sheet (Request it below.)
  • The cornstarch-iodine indicator
  • Glass stir stick or spoons
  • Optional: You might want to prep a small label with the name of each liquid and place it by the appropriate test tube or container where you will be conducting the titrations.
  • Measure 5 mL of the starch-iodine indicator and pour it into each test tube.

  • Have the recording sheet and pencil handy. You can request our measuring sheet below.
  • Using a clean pipette, begin dropping the first juice to be tested into the first test tube or whatever mixing container you are using. Dispense one drop at a time. Stir in between drops. If you do not have glass stir sticks, shake the test tube. When the liquid is colorless, record the number of drops dispensed to that point. This is the end of the titration.

  • Note: When we tested the EmergenC™, the indicator went colorless after six drops. The lemon juice took 21 drops, and the pumpkin, cranberries, and acorn squash took anywhere from 64 to 170 drops! Your results will vary, so no worries if it takes much more juice than expected to turn the indicator colorless.
  • Move on to the next liquid to be titrated. Repeat until finished.

  • Use the discussion questions to help your child communicate their findings.

Testing for Vitamin C with Iodine:  What Happened and Discussion Questions

When iodine is introduced into a mixture high in vitamin C, the ascorbic acid becomes oxidized. The hydrogen atoms found in ascorbic acid will combine with iodine to form iodide ions. This chemical reaction creates a colorless effect in liquids high in vitamin C.

When we tested our cranberry “juice,” it was difficult to tell when the titration ended because of the red color of the extracted juice. In your prep for this experiment, you may want to include a darker juice and ask your student what they think will happen. 

So, what exactly is happening in this experiment?

During titration, a chemical reaction takes place, and a process called an oxidation-reduction reaction occurs. The oxidation-reduction reaction is also referred to as redox.

 In an oxidation-reduction reaction, one substance in the reaction loses electrons (oxidation), and the other substance gains electrons (reduction). Reduction may sound counterintuitive, but reduction refers to the reduction of the receiving atom’s positive charge by gaining an extra negatively charged electron.

In this experiment, the vitamin C in the juices tested is oxidized (because it loses electrons), and the iodine is reduced (because it gains electrons.)

More About Titration

The titration process ends in this chemical reaction when the indicator is colorless. To determine the endpoint of the titration as accurately as possible, add one drop at a time, and stir or swirl the test tube after each addition. The titration is complete when the indicator is colorless (or reaches the desired color or lacks color).

In this experiment, the iodine solution is the titrant, the substance which is added to during titration. The liquids (lemon juice, acorn juice, cranberry juice) used are referred to as the analyte, the substance whose chemical makeup is analyzed and determined via titration.

Remind your student that atoms are never destroyed or created in a chemical reaction. In a chemical reaction, atoms are rearranged. The vitamin c molecule lost electrons in this experiment, and the iodine gained electrons.


Testing for Vitamin C with Iodine – Discussion

Please note the following is included in our printable. Request the printable using the sign-up box below.

  • Which liquid turned the indicator colorless with the least number of drops? What does this mean?
  • Which liquid took the most drops to turn the iodine colorless? Did all of the indicators turn colorless?
  • Looking at the amount of vitamin C per serving that you recorded on your lab worksheets, did the results of this experiment match the per serving information?

Download the free printable for this experiment. You will be added to our email community. We promise not to spam you! If the box below does not allow you to type in the boxes, please check for pop-up blockers on your browser. Also, do not include empty spaces at the beginning and end.

testing for vitamin c with iodine downlad the printables
Other Helpful Resources

Extract DNA from a Pumpkin

Big list of chemistry activities

Pumpkin STEM & Science Activities

The Benefits of Vitamin C and Why Your Child Needs it – The Cleveland Clinic

Vitamin C: Food, Functions, How Much Do You Need, and More – from the European Union Food Information Council

Free Radicals Information from the National Library of Medicine – The Abstract section of this study provides a concise explanation.

Understanding Anti-oxidants from Harvard Health

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