Chemical substances in foods

Step 2 Activity:
Iodide in table salt

Description and purpose of the activity

In this activity at first we use starch solution and iodine antiseptic solution in order to see the blue color which appears when these two materials react. After that we use the same procedure to analyze commercial products of table salt so that we can conclude if they contain iodine or not. The purpose of this activity is to simulate the procedure of a food analysis, like the procedures used by analytical chemistry labs, to determine the presence or not of an ingredient, by using materials which are common household items and not chemical reagents.

Apparatus

• 1 teaspoon
• 1 tablespoon
• Plastic spoons
• Plastic cups

Ingredients - Materials

• Distilled water
• Iodine antiseptic solution
• Hydrogen peroxide solution 3%
• White vinegar
• Corn starch
• Table salt (different types)

Procedure

1. Make a starch solution: Place ½ cup of water in a plastic cup and add 1/2 tablespoon of corn starch. Stir well.
2. Place ½ cup of water in a plastic cup and add ½ teaspoon of the starch solution we prepared in Step 1.
3. Add several drops of iodine antiseptic solution and stir well. You will notice that the solution becomes blue which confirms the presence of iodine in the antiseptic solution.
4. Put 4 tablespoons of iodized table salt in a plastic cup and add 1 cup of water. Stir well. The salt won’t dissolve completely.
5. Add in the solution 1 tablespoon of white vinegar, 1 tablespoon of hydrogen peroxide solution and ½ teaspoon of starch solution. Stir well and after a while the solution becomes blue which confirms the presence of iodine in the iodized table salt.
6. Repeat the procedure (Steps 4 and 5) using different types of salts.