Using a process known as titration, you can test for the vitamin C content in foods by measuring the amount of acid that's present. Vitamin C is an acid known as ascorbic acid and the titration method uses iodine to register the presence of this acid in your food. When ascorbic acid is present, the iodine will cause the solution to change color. Vitamin C is only present in fruits and vegetables. Most of the tools you need to perform this test are available at the drug store or at your grocery store. The only exception may be the iodine. If you cannot get it from your pharmacy, try an online retailer that specializes in supplies for science fair projects.
Step 1
Combine 3 tbsp. corn starch with 1 cup of distilled water in a 2-cup measuring cup.
Step 2
Extract juice from the fruit or vegetable that you want to test with a juicer. If you are testing more than one fruit or vegetable, juice them individually and wash the juicer between uses to avoid cross-contamination.
Step 3
Pulverize the fruits of vegetables in a blender and strain the liquid through a coffee filter if you do not have a juicer. If you are testing more than one food, pulverize them individually and wash the blender between uses.
Step 4
Leave premade liquid items, such as store bought juices, as is.
Step 5
Put the tester liquids in a 1-cup glass or plastic measuring cup. The number of measuring cups you need depends on the number of items you are testing.
Step 6
Pour 1 oz. of the tester liquid into a clear glass or plastic drinking cup.
Step 7
Use the eye dropper to drop 10 drops of the corn starch solution into the tester liquid. Stir the mixture with the Popsicle stick. The starch acts as an indicator, and will turn blue when it reacts with iodine.
Step 8
Add one drop of iodine to the tester liquid. Swirl the liquid for 20 seconds and observe whether the color changes. If the color does not change, add another drop and swirl. Continue adding one drop at a time and swirling for 20 seconds until the liquid changes color. When the liquid changes color and stays that way, stop adding iodine.
Tips and Warnings
- Iodine reacts immediately with vitamin C and the two substances cancel each other out. In the tester solution, the iodine will react with the vitamin C first. When there is more iodine than vitamin C in the solution, the iodine will then interact with the starch and turn the starch blue. The blue starch will make the liquid blue, greenish or a muddy brown depending on the original color of the fruit or vegetable. The more drops of iodine you have to add to make the color change, the higher the amount of vitamin C in that food.
Things You'll Need
- Corn starch
- Distilled water
- Glass or plastic 2-cup measuring cup
- Glass or plastic 1-cup measuring cups
- Juicer, optional
- Blender, optional
- Clear glass or plastic drinking cups
- Eye dropper
- Popsicle stick
- Iodine
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