Back to Hands-on Science Lessons | BOAST Home

Testing Vitamin C

1. Overview
2. Introduction
3. Materials
4. Instructions
5. Activity Questions
6. Assessment
7. Suggestions for Expanding the Activity
8. Learning Standards
   • Early Elementary
   • Late Elementary
   • National Standards

Overview

During this hands-on activity, students will test different juices for their vitamin C content. This activity demonstrates how to perform a titration. This activity is simple and inexpensive, yet it provides endless possibilities for lesson expansion and fullfillment of learning standards. You can incorporate a lesson on pH, acids, and bases into this lesson.

Introduction

Related Concepts

The concept that will be focused on for this lesson is performing a titration. In this activity, participants will determine how much Vitamin C is in a variety of juices and beverages.

Background Information

Participants are going to be performing a titration, a simple procedure for finding the concentrations or amounts of substances in solutions. In this test we will be using Vitamin C.

Before the activity can begin, starch solution must be added to the beverages that are to be tested. Iodine will then be added dropwise to each of the beverages. As iodine is added, it will first react with the ascorbic acid in the beverage, producing a colorless product (dehydroascorbic acid). When the ascorbic acid runs out, the iodine will react with the starch in the beverage. At this point, participants will be able to recognize a highly visible color change. This color change is the endpoint of the reaction. Therefore, the more iodine added, the more Vitamin C the beverage contained.

Getting the Lesson Started!

Here are some potential discussion questions

1. What vitamin is found in orange and lemon juice?
2. What other beverages do you think contain Vitamin C?
3. Of those you listed, which do you think contain the most?
4. Do you think there is a way that we can determine the amount of Vitamin C in each of the beverages?

Materials

• various juice drinks (we used orange juice, lemon juice, lemonade, orange HI-C, apple juice, and fruit flavored carbonated beverages, such as Sprite)
• a pipette for each beverage
• a plastic cup for each beverage
• iodine solution
• starch solution (consisting of 1 part baking soda to 5 parts water)
• toothpicks or stirring rods

Instructions

1. Pour about 1 ounce of each beverage into a separate plastic or paper cup.
   
2. With a pipette, add about 10 drops of the starch solution to each cup. Stir each solution with a toothpick or stirring rod.
   
3. Begin adding the iodine to one of the solutions a drop at a time. Make sure you count the number of drops you are adding. Stir the solution after the addition of each drop.
   
4. As drops are continually added, the solution will change color. When the solution first changes color, stir for at least 20 seconds. If the original color reappears, more iodine must be added. If the color change persists, you have reached the endpoint. (The right picture below shows an example of a beverage after it has reached the endpoint.)
   
5. Record the number of drops needed to reach the endpoint.
6. Repeat the above procedure for each of the solutions you are testing.

Activity Questions

Observations

Data Chart for Titrations

Directions: For each beverage, write the amount of drops used to change the color of the solution. Then rank the beverages in order from most Vitamin C to least.

Titration Graph

For each beverage, color in the amount of drops used to turn the beverage to a different color. If more than twenty drops are used, fill in the entire column and write the number of drops at the top of the column.

Questions

1. Which beverage had the least amount of Vitamin C in it? How do you know?
2. Which beverage had the greatest amount of Vitamin C in it? How do you know?
3. Were you surprised by any of the results? Explain.

Assessment

Assessment Background

Our assessment methods were the same for Illinois and National Standards.

Our assessment methods were the same and for Early and Late Elementary School students. What changed was the level of the questions asked and the discussion.

During the Lesson

The participants used inquiry strategies to successfully determine how to perform a titration. Throughout the lesson, the participants discussed the inter-relationships between science, technology, and society by discussing the importance of Vitamin C in our diet.

At the End of the Lesson

At the conclusion of the lesson, a discussion was held to determine the level of participant understanding of how and why a titration is performed. The discussion also encouraged students to think critically about the role of Vitamin C to our health.

Here is a sample of questions from that discussion:

• How is a titration performed?
• What does a titration tell us?
• Could a titration be done to determine other things besides Vitamin C content?
• Which tested beverages were high in Vitamin C?
• Were you surprosed by any of the results? Explain.

Each of the children who participated in the lesson was able to answer these questions at his/her own level.

Suggestions for Expanding the Activity

Testing the pH.

This lesson can be greatly expanded by adding the concepts of pH and acids and bases. While performing this lesson, it would be appropriate to measure the pH of each of the beverages as well. The pH can easily be determined with a pH indicator strip. Once the pH has been determined, students can decide if the beverage is a acid or a base. Since all of the beverages in the Vitamin C test are acids, you may want to add solutions that are bases such as Laundry detergent, antacid solution, cleaning products, etc.

Here is a sample chart for this information:

Directions: For each sample, write the pH. The write whether the sample was an acid or a base.

Illinois State and National Learning Standards that Apply to this Lesson

The following standards are from the Illinois Learning Standards, adopted by the Illinois State Board of Education on July 25, 1997. Take a look at the complete Illinois Learning Standards for Science, and for English/Language Arts.

Early Elementary

Late Elementary

National Learning Standards that Apply to this Lesson