How to Do a Science Project Trying to Find the Amount Vitamin C Concentration in Citrus Fruit

Titration can be used to estimate the concentration of vitamin C in citrus fruit.

Vitamin C is a water soluble vitamin and is essential for growth and development. Fruits and vegetables contain vitamin C, and some have more than others. Titration is a simple method of using color to indicate how much vitamin C is in a fresh fruit. In this procedure, iodine is used as the indicator solution and is added drop by drop to juice and mixed. Since iodine reacts quickly with vitamin C, a color change will be seen after iodine has oxidized the entire vitamin C content. A color change is noted by a final reaction with starch. The number of drops can then be calculated into an estimated concentration of the amount of vitamin C.

Things You'll Need

• Teaspoon
• Cornstarch
• Water
• Small pot
• Eyedropper
• 1/2 cup measuring cup
• Iodine
• Jars
• 2 cup measuring cup
• 1 tablet of 500 milligrams Vitamin C tablet, or two 250 milligram tablets (crushed)
• Paper
• Pen
• Citrus fruit
• Blender

Instructions

Indicator Solution

1. Add 1 teaspoon of cornstarch to cool water. The purpose is to make a paste, thus add more cornstarch or water, if need be.

2. Put the paste into a small pot and add 1 cup of water to the paste. Boil for five minutes.

3. Remove from heat, and let the cornstarch solution stand until cool.

4. Fill the eyedropper with the cornstarch solution. Add 20 drops of solution to half a cup of water.

5. Add iodine to half-cup solution until it produces a dark purple-blue color. This is the indicator solution.

Vitamin C Standard Reference

1. Fill a jar with two cups, or 500 milliliters, of distilled water.

2. Add the crushed 500 milligram, or two 250 milligram, tablets of vitamin C powder to the distilled water, and mix well. This solution makes 1 milligram per milliliter (mg/ml) of vitamin C

3. Add one tablespoon, or 20 milliliters, of the powder solution to 4 ounces, or half glass, of water.

4. Fill an eyedropper with indicator solution and slowly add one drop at a time to the half glass of water. Mix well after every drop.

5. Record how many drops it takes to change the vitamin C solution to a dark blue color. This is also known as a standard reference, meaning it took "x" amount of solution to change the color of a known amount of vitamin C. By using this reference, one can estimate the amount of vitamin C concentration fruit juices.

Experiment

1. Put citrus fruit in blender and blend well. Strain out the blended fruit to separate the pulp from the juice.

2. Add one tablespoon, or 20 milliliters, of the juice to 4 ounces, or half glass, of water.

3. Fill an eyedropper with indicator solution and slowly add one drop at a time to the half glass of water. Mix well after every drop.

4. Record how many drops it took to change the color of the juice.

5. Use the standard reference above to figure out concentration of vitamin C.

   Number drops in juice/ number of drops in vitamin C solution= concentration in milligram per milliliter (mg/ml)

6. Use this as an example:

   It took 44 drops of iodine solution to change the color of vitamin C solution

   It took 12 drops of iodine solution to change the color of the juice.

   Vitamin C in juice= 12/44

   Vitamin C in juice= .272 mg/mL

Tips & Warnings

• Peel fruits that have a tough rind, such as oranges and lemons, before blending.

• Always rinse eye dropper after each use.

• Adult supervision is needed if a child will be using a stove.

References

• Medline Plus: Vitamin C
• Science Project Lab: Vitamin C Science Project
• Nutrition Science Projects: Do different varieties of the same fruit have the same level of vitamin C?
• Onlin Digital Education Connection: Vitamin C

Resources

• Science Project Lab: Vitamin C Science Project