Jump to main content

Determining Iodide Content of Salt

361 reviews


Have you ever noticed that the salt you are using says it is "iodized"? Iodine is an important micronutrient, which means we need it in small quantities to be healthy. Because iodine is rare in many people's normal diets, it is added to table salt. Then when people salt their food, they are also adding this important micronutrient. In this food science project, you will use some kitchen-friendly chemistry to investigate which types of salt have iodine added (in the form of iodide) and which do not. Get ready to shake out some salt!


Areas of Science
Time Required
Average (6-10 days)
Material Availability
Readily available
Low ($20 - $50)
No issues

Teisha Rowland, PhD, Science Buddies

This science project idea is based on the following classroom activity by Stephen W. Wright of Pfizer Global Research and Development:


Test different types of salt to see if they contain iodine, a micronutrient.


Did you know that the number one thing people can do, world wide, to prevent mental retardation is to cook and season food with iodized salt? Here is why. Nutrients are chemicals that people need for their bodies to run normally and be healthy. Micronutrients, like iodine, are types of nutrients that people need in small amounts. Iodine is specifically very important for a person's thyroid to function normally. (The thyroid is a gland in the neck that makes key hormones.) If a person does not eat enough iodine in their diet, they can become iodine deficient. Iodine deficiency can cause different medical problems (usually due to hypothyroidism, or having a thyroid that does not make enough hormones). This includes goiter, which is a visible swelling of the thyroid, serious birth defects like cretinism, and brain damage. In fact, iodine deficiency is the most common cause of preventable mental retardation.

Iodine deficiency is completely preventable by making sure people get enough iodine in their diets, which is why iodine (in the form of iodide) is added to table salt. Iodine is rare in many people's normal diets, but if they use iodized salt, then when they salt their food they are also getting a small dose of this important micronutrient. Since the 1980s, efforts have been made to have universal salt iodization. This has been an affordable and effective way to combat iodine deficiency around the world. However, not all types of salt contain iodine.

In this food science project, you will use some kitchen-friendly chemistry to investigate which types of salt have iodine added to them. Which do you think will have iodine, and which do you think will not? To do this test you will use laundry starch, vinegar, and hydrogen peroxide. Iodine undergoes a chemical reaction with starch to make a blue-purple-colored chemical, as shown in Figure 1, below. This is how you can visibly see if there is iodine. Vinegar and hydrogen peroxide are added to the salt solution to help the iodine reaction with starch take place. Specifically, vinegar is an acid, and so when you add it you are changing the pH of the solution so that the reaction can take place. (You do not need to understand acids and pH to do this science project, but if you would like to find out more about them, you can check out the Science Buddies' resource Acids, Bases, & the pH Scale). Lastly, since salt has iodine in the form of iodide, you will add hydrogen peroxide to turn the iodide into iodine, which the starch will react with.

A violet colored solution and plastic spoon sit in a plastic cup labeled iodine

Figure 1. Within the correct pH range, starch undergoes a chemical reaction with iodine to turn it a blue-purple color, as shown here.

Terms and Concepts



This science project idea is based on the following classroom activity by Stephen W. Wright of Pfizer Global Research and Development:

Materials and Equipment

Disclaimer: Science Buddies participates in affiliate programs with Home Science Tools, Amazon.com, Carolina Biological, and Jameco Electronics. Proceeds from the affiliate programs help support Science Buddies, a 501(c)(3) public charity, and keep our resources free for everyone. Our top priority is student learning. If you have any comments (positive or negative) related to purchases you've made for science projects from recommendations on our site, please let us know. Write to us at scibuddy@sciencebuddies.org.

Experimental Procedure

Positive Control: Iodine-Starch Reaction

  1. Do your background research so that you are knowledgeable about the terms, concepts, and questions, in the Background section.
  2. Using a permanent marker, label one of the 10 ounce (or larger) plastic cups "Iodine."
  3. Pour 120 milliters (mL) (1/2 cup [C.]) of distilled water into the labeled cup.
  4. Add 2.5 mL (1/2 teaspoon [tsp.]) of laundry starch solution.
  5. Add five drops of iodine antiseptic solution and stir well with a clean, disposable plastic spoon. What do you observe? You should see the iodine turn a blue-purple color as it interacts with the starch solution, as shown in Figure 1, below.
    1. Record your results in your lab notebook.
    2. You could also take a picture of the cup to include on your Science Fair Display Board.
Liquid from an eye dropper reacts with clear liquid in a plastic cup turning the clear liquid blue

Figure 2. You should see the iodine turn a blue-purple color as it interacts with the starch solution.

Testing Various Types of Salt for the Presence of Iodide

  1. In your lab notebook, you could create a data table to record your results in. You will want to have a row for each type of salt you test (and the positive control iodine solution) and a column where you can record the color of each solution at the end of their test.
  2. Pick one of the types of salt to test. Using the permanent marker, label a clean, plastic cup with the type of salt that you are testing. Place 4 tablespoons (Tbsp.) (about 80 grams [g]) of the salt into the labeled cup, as shown in Figure 3, below.
A tablespoon of salt is poured into a plastic cup

Figure 3. For each type of salt you test, you will need to measure out 4 Tbsp. into a clean, disposable plastic cup.

  1. Add 240 mL (1 C.) of distilled water and stir well for about a minute with a clean, disposable plastic spoon. Not all of the salt will dissolve, but any iodide present in the salt will dissolve.
  2. Add 15 mL (1 Tbsp.) of white vinegar, as shown in Figure 4, below.
  3. Add 15 mL of 3% hydrogen peroxide.
A tablespoon of vinegar is added to a plastic cup

Figure 4. After mixing distilled water with the salt, add 1 Tbsp. of the vinegar and 1 Tbsp. of the hydrogen peroxide to help the chemical reaction between iodine and starch take place.

  1. Add 2.5 mL (1/2 tsp.) of the starch solution.
  2. Stir the salt solution well with the disposable plastic spoon (using the same spoon you already used with this solution), and then let it stand for a few minutes. Does the solution become a blue-purple color, indicating that it has iodine? Record your results in your lab notebook.
    1. You could also take a picture of your results to include on your Science Fair Display Board.
  3. Repeat steps 2-7 using different types of salt. Be sure to use a different, clean disposable cup and spoon for each different type of salt you test so you do not contaminate your results. Also record all of your results in your lab notebook and, if possible, take pictures.
  4. Analyze your results. Which types of salt have detectable amounts of iodine? Are you surprised by any of your results?
    1. Some types of salt say whether or not they contain iodine (in the form of iodide) on their packaging. Take a look at the containers for the different types of salt that you tested. Do your tests confirm, or disprove, the containers' labeling?
icon scientific method

Ask an Expert

Do you have specific questions about your science project? Our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.


  • In this science project, you added vinegar because it is an acid that helps the chemical reaction take place between the starch and the iodine. You could investigate the effect of pH on this chemical reaction by repeating the experiment but not using vinegar. Do you still get a blue-purple color when mixing an iodized salt solution with the hydrogen peroxide and starch, or do you get no color change at all? Or does the chemical reaction just take more time to happen? Hint: You may need to be patient to see the results of this experiment! To find out more about acids and pH, check out the Science Buddies' resource Acids, Bases, & the pH Scale.
  • The rate of the chemical reaction you explore in this science project can be affected by chemicals known as reducing agents. Corn syrup (which is primarily a solution of sugars with water) is a reducing agent you could experiment with. Try adding 1-2 tsp. of corn syrup to the iodized salt solution. How does adding the corn syrup affect how quickly the iodine changes color when it is mixed with the starch? You may need to do some research on the chemical reaction used in this science project, and reducing agents, to explain your results. You could start by looking at the Wright, S. W. (2007) resource listed in the Bibliography.
  • Temperature often affects chemical reactions. You could try this experiment again, but this time pick one salt solution that changed color and test it at different temperatures by using distilled water that has been cooled or heated to different temperatures. (You can measure and record the temperatures using a thermometer.) How does changing the temperature of the solution change how the color-changing reaction takes place?
  • For another Science Buddies project involving the exciting color-forming interactions of iodine and starch, see Investigate the Kinetics of the Color Changing Iodine Clock Reaction.


If you like this project, you might enjoy exploring these related careers:

Career Profile
There is a fraction of the world's population that doesn't have enough to eat or doesn't have access to food that is nutritionally rich. Food scientists or technologists work to find new sources of food that have the right nutrition levels and that are safe for human consumption. In fact, our nation's food supply depends on food scientists and technologists that test and develop foods that meet and exceed government food safety standards. If you are interested in combining biology, chemistry,… Read more
Career Profile
Everything in the environment, whether naturally occurring or of human design, is composed of chemicals. Chemists search for and use new knowledge about chemicals to develop new processes or products. Read more
Career Profile
Good taste, texture, quality, and safety are all very important in the food industry. Food science technicians test and catalog the physical and chemical properties of food to help ensure these aspects. Read more
Career Profile
The role that the chemical technician plays is the backbone of every chemical, semiconductor, and pharmaceutical manufacturing operation. Chemical technicians conduct experiments, record data, and help to implement new processes and procedures in the laboratory. If you enjoy hands-on work, then you might be interested in the career of a chemical technician. Read more

News Feed on This Topic

, ,

Cite This Page

General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

Science Buddies Staff. "Determining Iodide Content of Salt." Science Buddies, 8 July 2020, https://www.sciencebuddies.org/science-fair-projects/project-ideas/FoodSci_p011/cooking-food-science/determining-iodide-content-of-salt. Accessed 7 June 2023.

APA Style

Science Buddies Staff. (2020, July 8). Determining Iodide Content of Salt. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/FoodSci_p011/cooking-food-science/determining-iodide-content-of-salt

Last edit date: 2020-07-08
Free science fair projects.