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C. Stillman, January 2010

What’s a Pirate’s Favorite Drink?

Vitamin C is an important nutrient for your body. Your body can produce some Vitamin C itself, but in order to get enough to keep you healthy you must also eat and drink foods that contain it. Fruits and vegetables are the best sources of Vitamin C. The recommended amount of Vitamin C you need per day is 60mg.

The disease is caused when someone does not get enough vitamin C is called scurvy. This disease was common among pirates and sailors in the 1400s and 1500s because they were on the sea for longer than perishable fruits and vegetables could be stored.

In this lab you will study how much vitamin C is in a serving of some of your favorite drinks. The scientific procedure you will perform to determine this information is called a titration.

Pre-lab Question:

Predict the amount of Vitamin C each drink contains from least to most. Write your predictions on the arrow below.

THE TITRATION:

Test tube 1: Sunny D

(1)Measure 1 ml of Sunny D using a pipette and add it to a test tube.

(2)Add 1 drop of starch solution to the test tube and swirl gently.

(3)Using a clean pipette, add iodine solution to the test tube 1 drop at a timeuntil the sunny D just turns a gray/black color. Count the number of drops it takes and record this value on your data table below.

Test tube 2: Minute Maid Orange Juice

(1)Follow test tube 1 directions using Minute Maid.

(2)Be sure to record the number of drops it takes for the Minute Maid to turn a gray/black color.

Test tube 3: Milk

(1)Follow test tube 1 directions using milk (be careful to add only 1 drop at a time).

(2)Be sure to record the number of drops it takes for the milk to turn a gray/black color.

Test tube 4: Apple Juice

(1)Follow test tube 1 directions using apple juice.

(2) Be sure to record the number of drops it takes for the apple juice to turn a gray/black color.

DATA:

Sunny D Minute Maid Milk Apple Juice

# Iodine Drops

The Calculations:

Calculate the number of milligrams (mg) of Vitamin C in each 1 milliliter (ml) drink sample using the formula below. Show your work.

# mg Vitamin C = .053 (conversion factor) # drops iodine

(1) Sunny D:

(2) Minute Maid:

(3)Milk:

(4) Apple Juice:

Questions:

  1. Which drink took the most iodine drops before it changed color?
  1. Which drink contained the most Vitamin C? Was your pre-lab prediction correct?
  1. If there are 240ml in a serving of a drink, how much Vitamin C does each drink contain per serving? Show your work below. (Hint: your samples were 1 ml)

4. Imagine you are a pirate preparing for a long sailing adventure in a time before refrigerators and preservatives. Which drink would you pack for you and your crew to prevent them from getting scurvy?

Teacher Kit

Grade level/Subject: 4-6th grade Chemistry

Objective: The goal of this lab is to determine the amount of Vitamin C in various drink samples. Students will perform titrations and perform some basic calculations to determine the amount of Vitamin C in one serving (8 oz) of their favorite drinks.

Materials:

various drinks (I used Sunny D, Minute Maid, Milk, and Apple juice)

test tubes

pipettes

corn starch

iodine crystals (or purchase iodine solution from a drug store)

potassium iodide (KI) (available for purchase online from The Science Shop:

potassium iodate (KIO3 ) (available for purchase online from B & A products:

3M sulfuric acid (available from The Science Shop website)

beakers for solution preparation

distilled water for solution preparation

plastic cups for distributing drinks to stations

Preparing Solutions:

Starch indicator solution

  1. Add 0.5g corn starch to 50ml boiling water in beaker.
  2. Mix well and allow to cool before use.

Iodine Indicator Solution

  1. In a beaker, dissolve 5g of potassium iodide and .268g potassium iodate in 200 ml of distilled water.
  2. Add 30ml of 3M sulfuric acid. (CAUTION: Wear gloves for this step)
  3. Dilute this solution to a final volume of 500ml with distilled water.
  4. Mix the solution and label it as your iodine indicator.

Lead the Activity:

  • Have students read the introduction page (page 1) of their worksheets. Introduce the terms titration, end point and indicator.
  • titration- a scientific procedure that is used to determine the unknown concentration of a substance in a solution.
  • End-point- the point where the titration is complete. This is usually shown by a color change of the indicator.
  • indicator - a chemical that is added to a sample during a titration to detect the presence of some substance. When the titration is complete the indicator will make the sample turn color because there is no more of that substance left in the sample.
  • Have the students fill out the pre-lab question.
  • Next divide the class into 4 groups and send 1 group to each of the four stations.
  • The groups should rotate through the stations and follow the directions in their packet for each station. Be sure to stress the importance of counting the number of drops it takes for the drink sample to reach the end point, or to just turn a gray/black color (indicating that no more vitamin C is left to bind to the starch).
  • Students should count and record the number of drops to reach the end point in their data table.
  • Next, students will calculate the amount (mg) each of their 1ml samples contains. This is done by multiplying the number of iodine drops used for each sample by the conversion factor, or a ratio that converts the counted drops of iodine to a mass of Vitamin C. The conversion factor for this experiment is 1mg Vitamin C/19 drops iodine or .053.
  • Students should then answer the post-lab questions. The last question would bridge nicely to a history lesson.

Safety Information:

  • The sulfuric acid used to make the iodine indicator solution is very corrosive. Wear gloves at all times when handling.
  • Iodine indicator stains. Be sure to have paper towels handy and to reiterate to students to be very careful when using the pipettes.

Expected Results:

Sunny D Minute Maid Milk Apple Juice

# Iodine Drops / 11-12 drops / 18 drops / 1-2 drops / 3-4 drops

How it works:

Vitamin C is a powerful antioxidant and is readily oxidized by iodine. When starch is added it reacts with the Vitamin C in the sample and adds some iodine into the mixture. When the iodine indicator is added, it only reacts with the Vitamin C and ignores the starch. When there is no more Vitamin C left to react with the iodine, the starch reacts with the iodine forming the blue/black precipitate seen at the titration’s end point. The starch acts as the indicator in the titration because it lets us know that all the Vitamin C has reacted with the iodine. By finding out how much iodine it takes to use up the Vitamin C, we can determine the amount of Vitamin C present in the sample.

Answers to Questions:

  1. The Minute Maid took the most drops to reach the end point. This is because it contains the most vitamin C per serving.
  2. Minute Maid contains the most vitamin C (can be concluded qualitatively from observing the endpoint or can be calculated by multiplying the number of drops of iodine soln. used by .053)
  3. Answers may vary depending on student’s results, but amount of Vitamin C per serving should be the number of mg in their 1ml drink sample multiplied by 240ml (the number of ml in 1 serving of drink)

References

Helmenstine, A., M. “Vitamin C Determination by Iodine Titration”. About.com Chemistry.2001. The Chemical Heritage Foundation. Accessed January 7, 2010. <

“Vitamin C Science Project”. Science Project Lab. Accessed January 7, 2010.