Salty Science: Is There Iodine In Your Salt?
Have you ever noticed that the salt you’re using says it’s “iodized”? Iodine is a micronutrient, which means we need it in small quantities to be healthy. Because iodine is relatively rare in many people’s normal diets, it’s added to table salt. Then when people salt their food, like tasty turkey, stuffing and mashed potatoes, they’re also getting some iodine. In this science activity, you’ll use some kitchen-friendly chemistry to investigate which types of salt have iodine and which don’t. Then when you sit down to your Thanksgiving dinner, you can know whether to also give thanks that you’re helping combat iodine deficiency.
This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.
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 doesn’t eat enough iodine, 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 (a visible swelling of the thyroid), serious birth defects like cretinism and brain damage. In fact, iodine deficiency is the most common cause of mental retardation that could be prevented.
Iodine deficiency is 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. Since the 1980s, there’ve been efforts to have universal salt iodization. This has been an affordable and effective way to combat iodine deficiency around the world, but not all salt contains iodine. You’ll investigate whether different salts have iodine by mixing them with laundry starch, which forms a blue-purple-colored chemical with iodine. (Vinegar and hydrogen peroxide are added to the salt solution to help this chemical reaction take place.)
Extra: Try this activity with even more different types of salts. For some ideas, see the Materials list, above. Which types of salt contain iodine and which do not? Do your results agree with their labeling?
Extra: In this activity, you added vinegar because it is an acid and helps the chemical reaction take place. Try testing the iodized salt solution again but this time leave out the vinegar. Does the reaction still take place, turning the solution a blue-purple color? Does the reaction take a longer amount of time to happen?
Extra: Temperature often affects chemical reactions. You could try this activity again, but test an iodized salt solution at different temperatures (by heating or cooling the distilled water). How does changing the temperature of the solution change how the color-changing reaction takes place?
Observations and Results
Did the iodized table salt solution change to a blue-purple color when you mixed in the starch? Did the “lite” table salt similarly change color, while most of the other salt types did not?
In this activity you should have seen that the iodized table salt and the “lite” table salt solutions both changed color to a blue-purple color (as did the iodine antiseptic solution, if you used it). This indicates that iodide is present in these types of salts. You likely saw no color change for the solutions made using the non-iodized salt, rock salt, kosher salt or sea salt because these types of salt do not typically contain iodide.
The starch solution was used in this activity because it forms a blue-purple-colored chemical with iodine. Because the original pH of the solution needs to be changed for this chemical reaction to effectively take place, vinegar (an acid) is also added. Hydrogen peroxide is used to turn the salt’s iodide into iodine, which the starch reacts with.
More to Explore
Teisha Rowland, PhD, Science Buddies
Science Buddies |
Nutrients, diet, food, health, chemical reactions
Explore Our Science Videos
Build an Infinity Mirror
How to Build a Brushbot
Colorful Melting Ice Ball Patterns - STEM Activity