Abstract

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!

Objective

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

Introduction

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.

Terms and Concepts

• Nutrients
• Micronutrients
• Iodine
• Iodine deficiency
• Goiter
• Iodized salt
• Chemical reaction

Questions

• What medical complications can happen if someone has iodine deficiency?
• Assuming iodized table salt contains 0.006% iodide by mass, how much iodized salt would a person need to consume each day in order to get the recommended 150 micrograms of iodide?
• How can you tell if iodine has chemically reacted with starch?
• Which types of salt do you think will have iodine (in the form of iodide), and which do you think will not? Why? Hint: Look at the labeling on the packaging for the different types of salt.

Materials and Equipment

• Permanent marker
• Disposable plastic cups, 10-oz. or larger (at least 6). You will need one for the positive control iodine solution and one for each type of salt you want to test.
  • Tip: In order to see the iodine-starch reaction, the cups should be clear plastic or colored plastic with white interior.
• 100 mL graduated cylinder. Graduated cylinders are available online through suppliers such as Carolina Biological. Alternatively you could use measuring cups.
• Distilled water (at least 1.5 L)
  • Note: Using tap water can produce erratic results.
• 10 mL graduated cylinder. Graduated cylinders are available online through suppliers such as Carolina Biological. Alternatively you could use measuring spoons.
• Laundry starch solution, also called liquid starch (at least 15 mL). This can be found in the laundry detergent section of the grocery store.
  • If you cannot find laundry starch solution, you can make a starch solution by mixing 5 g (1 to 2 tsp.) cornstarch with 30 mL (2 Tbsp.) cold water, stirring this solution into 500 mL (2 C) of vigorously boiling water, and then allowing it all to cool. Be sure to have an adult help you if you use a stovetop. Alternatively, 1 C of starch-based biodegradable packing peanuts could be dissolved in 500 mL water to make a suitable starch solution.
• Iodine antiseptic solution (5 drops)
  • Use either an iodine tincture or povidone-iodine solution, found in the first aid section of grocery stores and drugstores.
• Medicine dropper. This is in the first aid section of grocery stores and drugstores.
• Disposable plastic spoons (at least 6). You will need one for the positive control and one for each type of salt you want to test.
• At least five different types of salt (4 Tbsp, or about 80 g, of each). For example:
  • Plain (non-iodized) table salt
  • Iodized table salt
  • Pickling salt
  • Rock salt, such as is used for making ice cream. Be sure to filter any dirt from the solution before testing.
  • Kosher salt
  • "Lite" salt
  • Sea salt
  • Note: Some nations permit the use of potassium iodate (KIO3) as an iodine supplement in iodized salt. The procedure used in this science project will not detect iodine added as potassium iodate. The U.S. Food and Drug Administration (FDA) has not approved the use of potassium iodate as a food additive in the U.S.
• 3% hydrogen peroxide solution (at least 75 mL)
• White vinegar (at least 75 mL)
• Optional: Camera
• Lab notebook

Experimental Procedure

Variations

Careers

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

Related Links

• Science Fair Project Guide
• Other Ideas Like This
• Cooking & Food Science Project Ideas
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• Chemistry Safety Guide
• Visualizing Molecules in Three Dimensions

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