Which type of orange juice has the most vitamin C? In this science project, you will learn how to measure the amount of
vitamin C in a solution using an iodine titration method. You will compare the amount of vitamin C in three different types
of orange juice: homemade, premium not-from-concentrate, and orange juice made from frozen concentrate. Which do
you think will have the most vitamin C?
Which Orange Juice Has the Most Vitamin C?
Objective
Kit Contents
To determine which orange juice has the most vitamin C: homemade fresh-squeezed, premium not-from-concentrate, or
orange juice made from frozen concentrate.
QTY
ITEM DESCRIPTION
1
Juicer
1
Cheesecloth, 18" x 18"
1
Vitamin C tablets (250 mg), pack/5
1
Masking tape
1
Permanent marker
1
Goggles, Chemical Splash, ANSI Certified
1
Lab apron, rubberized
1
Lugol's iodine solution, 30 mL
1
Soluble starch, 30 g
1
Funnel, small, plastic
1
50 mL graduated cylinder, poly
1
500 mL graduated cylinder, poly
1
50 mL Ehrlenmeyer flask, glass
1
50 mL burette, acrylic
1
Ring stand, 4x6 base, 18 inch rod
1
Buret clamp, Lincoln style
2
Plastic eyedropper
1
Measuring scoop
2
Glass bottle, 8 oz, amber
1
Beaker, glass, 100 mL
2
Nitrile gloves, standard, pair
1
MSDS Sheets
1
Lab notebook
Summary
Safety
Adult supervision required. Concentrated iodine is poisonous if swallowed. Read and follow all
safety guidelines in the Procedure. More information is available from the iodine Materials
Safety Data Sheet (http://www.hometrainingtools.com/images/art/CH-IODINE.pdf) .
Introduction
In this science project, you will determine the amount of vitamin C in various types of orange juice. You will use a method
called titration, which is a common technique in chemistry. Titration is a way to measure the unknown amount of a
chemical in a solution (the titrant) by adding a measured amount of a chemical with a known concentration (the titrating
solution). The titrating solution reacts with the titrant, and the endpoint of the reaction is monitored in some way. The
concentration of the titrant can now be calculated from the amount of titrating solution added and the ratio of the two
chemicals in the chemical equation for the reaction.
Let us go through the titration process with a specific example: the titration of vitamin C by iodine. The chemical name for
vitamin C is ascorbic acid. When iodine and ascorbic acid are combined in solution, a chemical reaction takes place. In
this chemical reaction, the ascorbic acid molecule loses electrons, which are transferred to the iodine molecule. Chemists
call this type of reaction an oxidation/reduction reaction (or redox reaction for short). The ascorbic acid is oxidized to
dehydroascorbic acid, and the iodine is reduced to iodide ions. Oxidation-reduction reactions always occur in pairs like
this. The molecule that loses electrons is oxidized, and the molecule that accepts the electrons is reduced.
So how can you use the iodine-ascorbic acid reaction to determine the amount of ascorbic acid (vitamin C)? If you start
with a known concentration of iodine, and carefully measure the amount of the iodine solution that you add, you can
calculate how much ascorbic acid was present. How do you know when the iodine-ascorbic acid reaction is complete?
You add an indicator to the solution. In this case, the indicator is soluble starch. When iodine reacts with starch, it turns
the solution a blue-black color. If ascorbic acid is present in the solution, iodine will react with it, and not with the starch,
so the solution will not change color. However, once all of the ascorbic acid has been oxidized, added iodine will be free
to react with the starch, producing a distinct color change.
In this chemistry science project, you will investigate which type of orange juice has more vitamin C (ascorbic acid):
homemade fresh-squeezed, premium not-from-concentrate, or orange juice made from frozen concentrate. Which do you
think it will be? You can find out for yourself with this science project!
Terms and Concepts
Titration
Ascorbic acid
Iodine
Oxidation / reduction reaction
Indicator
Questions
What happens when iodine is added to a starch solution?
What happens when iodine is added to a starch solution that also contains vitamin C?
Frequently Asked
Questions
Bibliography
http://www.sciencebuddies.org/science-fair-projects/project_ideas/Chem_p044.shtml#help
For a good, basic reference on chemistry, see:
Rader, A. (n.d.). Chem4Kids. Andrew Rader Studios. Retrieved July 18, 2007, from http://www.chem4kids.com
(http://www.chem4kids.com)
Abstract
The Materials Safety Data Sheet for Lugol's iodine solution has important chemical safety information:
Home Science Tools. (n.d.). Material Safety Data Sheet: Iodine Potassium Iodide Solution. Home Training Tools,
Chem_p044_20140225.pdf
APE-5208-KIT
Ltd. Retrieved November 3, 2013, from http://www.hometrainingtools.com/images/art/CH-IODINE.pdf
(http://www.hometrainingtools.com/images/art/CH-IODINE.pdf)
This science project is based on:
University of Canterbury. (n.d.). Determination of Vitamin C Concentration by Titration. Outreach, College of
Science. Retrieved July 18, 2007, from
http://www.outreach.canterbury.ac.nz/chemistry/documents/vitaminc_iodine.pdf
(http://www.outreach.canterbury.ac.nz/chemistry/documents/vitaminc_iodine.pdf)
Ganong, B. (n.d.). Determination of Vitamin C in Orange Juice. Mansfield University. Retrieved July 18, 2007, from
http://faculty.mansfield.edu/bganong/biochemistry/vitaminc.htm (http://faculty.mansfield.edu/bganong/biochemistry/vitaminc.htm)
Another useful reference on the vitamin C titration procedure is:
Helmenstine, A.M., 2007. (n.d.). Vitamin C Determination by Iodine Titration. About.com: Chemistry. Retrieved July
18, 2007, from http://chemistry.about.com/od/demonstrationsexperiments/ss/vitctitration.htm
(http://chemistry.about.com/od/demonstrationsexperiments/ss/vitctitration.htm)
More advanced students should do background research on stoichiometry and oxidation-reduction (redox) reactions.
Here is a helpful review of high school chemistry that can be a good starting point:
Shodor Education Foundation, Inc. (October 6, 2002). Stoichiometry. The University of North Carolina at Chapel
Hill. Department of Chemistry. Retrieved July 18, 2007, from http://www.shodor.org/unchem/basic/stoic/index.html
(http://www.shodor.org/unchem/basic/stoic/index.html)
Shodor Education Foundation, Inc. (n.d.). Redox Reactions. The University of North Carolina at Chapel Hill.
Department of Chemistry. Retrieved July 18, 2007, from http://www.shodor.org/unchem/advanced/redox/index.html
(http://www.shodor.org/unchem/advanced/redox/index.html)
Experimental Procedure
Caution: Iodine solution is poisonous. Avoid skin and eye contact. See the Materials Safety Data Sheet
(http://www.hometrainingtools.com/images/art/CH-IODINE.pdf) for complete information. Wear chemical safety goggles and rubber
gloves when handling the concentrated solution. Iodine solution will stain clothing; a lab coat or apron is also
recommended. For more information on how to properly use a balance and different titration techniques see
Chemistry Lab Techniques (http://www.sciencebuddies.org/science-fair-projects/project_ideas/Chem_Lab_Techniques.shtml) .
1. Do your background research so that you are knowledgeable about the terms, concepts, and questions, in the
Background (http://www.sciencebuddies.org/science-fair-projects/project_ideas/Chem_p044.shtml#background) section. For information about
doing a titration, visit the Science Buddies webpage Titration Tutorial: Tips & Tricks for Titrating
(http://www.sciencebuddies.org/science-fair-projects/titration_tutorial.shtml) .
2. Wear gloves, chemical safety goggles, and a lab coat or apron when using the iodine solutions in this experiment.
Also, if you are not working on a surface that can be stained, you should completely cover the surface with
newspaper to protect it.
3. Dilute the Lugol's iodine solution 1:10 in distilled water to make your iodine titration solution.
a. Carefully pour 30 milliliters (mL) of Lugol's solution into the 500 mL graduated cylinder. This amount should
be the entire bottle that comes with the Science Buddies kit.
b. Add enough distilled water to bring the total fluid volume to 300 mL and mix, as shown in Figure 1, below.
Chem_p044_20140225.pdf
Figure 1. After adding the 30 mL of Lugol's iodine solution to the 500 mL graduated cylinder, add enough
distilled water to bring the total fluid volume up to 300 mL.
c. Slowly and carefully pour the diluted solution into an amber glass bottle. You should use a funnel to do this.
i. Caution: The amber glass bottles that come with the Science Buddies kit hold about 230 mL each.
This means you will need to use both bottles to store the 300 mL of solution. Be careful when filling
the first bottle so that it does not overflow!
d. Label the bottle(s), such as by using a permanent marker and masking tape.
e. You can store the solution in its tightly sealed bottle(s) for now.
i. Note: Iodine is light-sensitive. Storing the solution in an amber glass bottle (or an aluminum foilcovered bottle), or in a dark location, protects it from light.
f. Rinse and dry the 500 mL graduated cylinder.
4. Make a starch indicator solution. This can be anywhere from 0.5 to 1.0%. The exact amount of starch is not critical.
a. Heat 200 mL of distilled water in a pot on the stove.
b. When it is near boiling, for a 0.5% solution, add 1 gram (g) (which is equivalent to 1/4 teaspoon) of soluble
starch to the pot.
c. Stir to dissolve the starch, while keeping the water near boiling.
i. Because even "soluble" starch is not very soluble, it may take about 15 minutes or more of stirring
the starch to dissolve it in the near-boiling water.
d. After the starch is dissolved in the water, remove the pot from the burner and allow the solution to cool.
e. When cool, store the starch solution (at room temperature) in a clean, tightly covered glass jar that is clearly
labeled.
f. Rinse and dry the 500 mL graduated cylinder.
5. Make a fresh vitamin C standard solution (at a concentration of 1 milligram [mg] per milliliter, or 1 mg/mL). Do this
on each day that you measure the vitamin C in your orange juice samples.
a. You will use this solution to "standardize" your iodine titration solution. You will measure how much of your
iodine solution it takes to oxidize a known amount of vitamin C. You can then use your iodine titration
solution to determine the amount of vitamin C from test samples of different orange juices.
b. Using a cutting board and a knife, crush a 250 mg vitamin C tablet into powder and carefully transfer all of
the powder to a bowl, as shown in Figure 2, below.
APE-5208-KIT
Figure 2. Crush the vitamin C tablet into powder and then transfer all of it to a bowl.
Figure 4. Carefully transfer the 100 mL of dissolved vitamin C into the 500 mL graduated cylinder and fill it with
distilled water until the total volume is 250 mL.
c. Dissolve the powdered vitamin C tablet in 100 mL of distilled water, as shown in Figure 3, below.
6. Set up the 50 mL buret on the ring stand, as shown in Figure 5, below.
a. You will first need to assemble the ring stand from the Science Buddies kit. To do this, screw the metal rod
into the black metal base. Then tightly screw the buret clamp into position on the top of the ring stand's
metal rod, as shown in Figure 5.
b. To set up the 50 mL buret on the ring stand, carefully slide it into place between the prongs of the buret
clamp, as shown in Figure 6, below.
Figure 3. Dissolve the powdered vitamin C tablet in 100 mL distilled water.
d. Pour the dissolved Vitamin C into the cleaned and dried 500 mL graduated cylinder and add distilled water
to bring the total volume to 250 mL, as shown in Figure 4, below. You now have a vitamin C standard
solution at a concentration of 1 mg/mL.
Figure 5. Assemble the ring stand, buret clamp, and buret, as shown here.
Chem_p044_20140225.pdf
APE-5208-KIT
Figure 6. Carefully slide the buret into place between the prongs of the buret clamp.
7. Titrate 20 mL of vitamin C standard solution.
a. Use the 50 mL graduated cylinder to measure 20 mL of vitamin C standard solution.
b. Pour this into the 50 mL Erlenmeyer flask, as shown in Figure 7, below. The shape of this flask allows you
to swirl the solution to mix it without spilling.
Figure 8. Adjust the buret's position so you can place the 50 mL Erlenmeyer flask right underneath it.
e. Make sure the bottom of the buret is turned to the closed position. This is done by turning the red stopper to
the horizontal position, as shown in the close-up in Figure 9, below, for the buret from the Science Buddies
kit.
Figure 7. Pour 20 mL of the vitamin C solution into the 50 mL Erlenmeyer flask.
c. Add 10 drops of starch indicator solution to the Erlenmeyer flask.
d. Carefully adjust the position of the buret on the ring stand so that you can place the Erlenmeyer flask
(containing the vitamin C and starch solutions) right under the buret, as shown in Figure 8, below. Leave the
Erlenmeyer flask there.
Figure 9. Make sure the buret is turned to the closed position, as shown here with the buret from the
Science Buddies kit.
f. Use the funnel to carefully fill the buret with the diluted Lugol's iodine solution you prepared in step 3. Fill it
somewhere between the 5 mL and 35 mL marks on the buret. The exact position is not important, as long
as the fluid level is not past the graduated markings on the top of the buret.
Chem_p044_20140225.pdf
APE-5208-KIT
g. To make sure your measurements are accurate, fill the tip of the buret with the diluted Lugol's iodine
solution. To do this, put an extra beaker below the buret and slowly turn the red stopper at the bottom of the
buret (to the vertical position) to let a few drops of titrating solution flow into the beaker (or just let enough
solution flow so that the entire tip of the buret is full of solution). Then, making sure the bottom of the buret
is closed again, place the Erlenmeyer flask back under the buret.
h. In your lab notebook, write down the initial level (in mL) of the iodine solution in the buret. Read the level
from the bottom of the meniscus, which is the curved surface of the liquid.
i. For example, in Figure 10, below, the level should be recorded as 21.85 mL, since this is where the
bottom of the meniscus is.
Figure 10. When reading the level of liquid in the buret, read from the bottom of the meniscus, which is
being pointed to with a black arrow in this picture. For example, the level of the liquid in this buret should
be read as 21.85 mL. (Note: The long white line at the top of the buret is the mark for 21 mL.)
i. Slowly turn the red stopper at the bottom of the buret until just one drop of the iodine solution comes out into
the Erlenmeyer flask below it. Then close the buret again.
i. Note: It is important to only let the iodine solution be added one drop at a time because the titration
reaction is very sensitive. One drop can be enough to drive the reaction to completion (if it were near
completion before). If more than one drop is added at a time, the data will not be as accurate as it
could be.
j. After each drop is added, swirl the flask to mix in the iodine solution.
i. When adding the iodine solution, you may see a temporary color change that goes away when you
swirl the flask, as shown in Figure 11, below.
Figure 11. When you add a drop of iodine solution, you may see a temporary color change, as shown here
(the dark blue swirls), that goes away when the iodine solution is mixed in the flask by swirling it.
k. Continue adding the iodine solution, mixing in one drop at a time and swirling the flask, until the iodine
creates a blue-back color throughout the solution, as shown in Figure 12, below, that lasts for longer than
20 seconds. At this point, the titration is complete.
Figure 12. When the entire solution in the flask changes to a blue-black color that lasts for more than 20
seconds while swirling it, the titration is complete.
l. In your lab notebook, record the final level of the iodine solution remaining in the buret.
m. The difference between the initial level and the final level is the amount of iodine titration solution needed to
oxidize the vitamin C.
n. Rinse out and dry the Erlenmeyer flask.
o. Repeat step 7 three times. You should get results that are within about 0.2 mL of each other. If you do not,
repeat this step until you have three results that are within about 0.2 mL of each other.
i. Be sure to check the level of the iodine solution in the buret before each trial. Remember, if the level
is below the 35 mL mark, carefully add more iodine solution to the buret (until it is between the 5 mL
and 35 mL marks). Record the new level.
8. Prepare fresh-squeezed orange juice for testing.
a. Use the juicer to extract orange juice from three (or more) oranges, as shown in Figure 13, below.
b. You need 20 mL of juice per titration, and you should do at least three titrations of the fresh-squeezed
orange juice, so you will need at least 60 mL total.
Chem_p044_20140225.pdf
APE-5208-KIT
c. Filter the orange juice through cheesecloth to remove any pulp and seeds.
10. Titrate your other orange juice samples by repeating step 9 using the premium not-from-concentrate orange juice
and the orange juice made from frozen concentrate (separately).
a. If you test the orange juice samples on different days, be sure to make a fresh vitamin C standard solution
on each day that you measure the vitamin C in your orange juice samples.
11. For each juice (fresh, premium, or from-concentrate), calculate the average amount of iodine needed to titrate the
20 mL sample. Record your results in your lab notebook.
12. Calculate the amount of vitamin C in your samples by setting up a proportion, as shown in Equation 1, below. You
will want to solve for Vitamin C2
Equation 1.
Iodine1 is the average amount of iodine (in mL) needed to titrate the vitamin C standard solution.
Vitamin C1 is the amount of vitamin C in the standard solution (in mg).
Iodine2 is the average amount of iodine (in mL) needed to titrate the orange juice sample.
Vitamin C2 is the amount of vitamin C in the orange juice sample (in mg).
a. You can rearrange Equation 1 to directly solve for the unknown "Vitamin C 2" value, resulting in Equation 2,
below.
i. If you are not sure how Equation 2 was derived from Equation 1, take a moment to examine the
equations so that you understand the derivation process.
Figure 13. Use a juicer, like the one shown here from the Science Buddies kit, to juice at least three oranges. You
will need to cut each orange in half to use this juicer.
9. Titrate the fresh-squeezed orange juice you just prepared by repeating step 7, but this time, use 20 mL of freshsqueezed orange juice in the Erlenmeyer flask instead of 20 mL of the vitamin C solution.
a. Be sure to check the level of the iodine solution in the buret before each trial. Remember, if the level is
below the 35 mL mark, carefully add more iodine solution to the buret (until it is between the 5 mL and 35
mL marks). Record the new level.
b. In step 7.k., the titration is complete when the iodine creates a distinct color change in the juice/starch
solution. This color change will be harder to see than with the vitamin C solution, since the juice starts out
orange. The color will change from orange to grayish brown when the endpoint is reached, as shown in
Figure 14, below. If you continue to add iodine, the color will darken further, but you want to note the volume
of iodine added when the color first changes.
c. Remember to record the final level of the iodine solution in the buret, as done in step 7.l.
d. The difference between the initial level and the final level is the amount of iodine titration solution needed to
oxidize the vitamin C in the orange juice.
e. As you did for step 7.o., repeat the titration process for the fresh-squeezed orange juice a total of three
times. You should get results that are within about 0.2 mL of each other.
Equation 2.
b. Here is an example (with sample numbers) to show you how to use Equation 2:
i. Let us say that it took an average of 8.5 mL of iodine solution to titrate 20 mL of 1 mg/mL vitamin C
standard solution. 20 mL of the vitamin C solution is equal to 20 mg vitamin C total. This means that
"Iodine1" equals 8.5 mL and "Vitamin C1" equals 20 mg.
ii. Let us also say it takes an average of 6.8 mL of iodine solution to titrate a 20 mL test sample of
orange juice. This means that "Iodine 2" equals 6.8 mL.
iii. Using this example, we would set up Equation 2 to look like Equation 3, below. Note that we do not
know "Vitamin C2" because that is what we are solving for.
Equation 3.
iv. When solving for Vitamin C2 in Equation 3, we get an answer of 16 mg. This means there is 16 mg of
vitamin C in that orange juice sample.
13. Graph your results, putting the names of the different kinds of orange juice on the x-axis and the average amount
of vitamin C on the y-axis.
14. Look at your graphs. Did one type of orange juice have more vitamin C than the others? Why do you think this
might be? Can you explain your results?
Variations
Figure 14. When the titration is complete with the orange juice sample, the entire orange juice sample will turn
from orange to grayish brown in color, as shown here.
Chem_p044_20140225.pdf
Measure the amount of vitamin C in fresh fruits and vegetables. Which ones have the highest vitamin C content?
Which ones have the lowest? Puree a 100 g sample of the fruit or vegetable, and strain it through cheesecloth with
about 50 mL of distilled water. Add distilled water to bring the total volume up to 100 mL. From your measurement,
you can figure out how much vitamin C there is per 100 g of the fruit or vegetable you sampled. You can use
typical weights of the fruit or vegetable to calculate how much total vitamin C there is in each fruit or vegetable you
test.
Measure the vitamin C content in fruit juices. Do the amounts correspond to what is on the label? Design an
APE-5208-KIT
experiment to find out.
Does the amount of vitamin C in fruit juice decrease during refrigerated storage? Does the type of container (e.g.,
glass bottle, or paperboard carton) matter? Design an experiment to find out.
For an experiment on how storage affects the amount of vitamin C in oranges, see the Science Buddies project Do
Oranges Lose or Gain Vitamin C After Being Picked? (http://www.sciencebuddies.org/science-fair-projects/project_ideas/Chem_p043.shtml)
Related Links
University of Canterbury. (n.d.). Determination of Vitamin C Concentration by Titration. Outreach, College of
Science. Retrieved July 8, 2007, from
http://www.outreach.canterbury.ac.nz/chemistry/documents/vitaminc_iodine.pdf
(http://www.outreach.canterbury.ac.nz/chemistry/documents/vitaminc_iodine.pdf)
Last edit date: 2014-02-26
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If you have purchased a kit for this project from Science Buddies, we are pleased to answer any question not addressed
by the FAQs on our site. Please email us at [email protected] (mailto:[email protected]?
Chemistry Safety Guide (http://www.sciencebuddies.org/science-fair-projects/project_ideas/Chem_Safety.shtml)
subject=Which%20Orange%20Juice%20Has%20the%20Most%20Vitamin%20C?)
Titration Tutorial: Tips & Tricks for Titrating (http://www.sciencebuddies.org/science-fair-projects/titration_tutorial.shtml)
PI at http://www.sciencebuddies.org/science-fair-projects/project_ideas/Chem_p044.shtml#help
If you like this project, you might enjoy exploring these related careers:
Food Scientist or Technologist
There is a fraction of the world's population that doesn't have enough to eat or doesn't
have access to food that is nutritionally rich. Food scientists or technologists work to
find new sources of food that have the right nutrition levels and that are safe for human
consumption. In fact, our nation's food supply depends on food scientists and
technologists that test and develop foods that meet and exceed government food safety
standards. If you are interested in combining biology, chemistry, and the knowledge that you are helping people, then a
career as a food scientist or technologist could be a great choice for you! Read more (http://www.sciencebuddies.org/science-fairprojects/science-engineering-careers/FoodSci_foodscientistortechnologist_c001.shtml)
after you have checked the Frequently Asked Questions for this
In your email, please follow these instructions:
1. What is your Science Buddies kit order number?
2. Please describe how you need help as thoroughly as possible:
Examples
Good Question I'm trying to do Experimental Procedure step #5, "Scrape the insulation from the wire. . ." How do
I know when I've scraped enough?
Good Question I'm at Experimental Procedure step #7, "Move the magnet back and forth . . ." and the LED is not
lighting up.
Bad Question I don't understand the instructions. Help!
Dietitian or Nutritionist
Ever wondered who plans the school lunch, food for patients at a hospital, or the meals
for athletes at the Olympics? The answer is dietitians and nutritionists! A dietitian or
nutritionist's job is to supervise the planning and preparation of meals to ensure that
people—like students, patients, and athletes—are getting the right foods to make them
as healthy and as strong as possible. Some dietitians and nutritionists also work to
educate people about good food choices so they can cook and eat their own healthy meals. Read more
Typesetting math: 100%
(http://www.sciencebuddies.org/science-fair-projects/science-engineering-careers/FoodSci_dietitianornutritionist_c001.shtml)
Chemist
Everything in the environment, whether naturally occurring or of human design, is
composed of chemicals. Chemists search for and use new knowledge about chemicals
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Credits
Andrew Olson, PhD, Science Buddies
Teisha Rowland, PhD, Science Buddies
Tropicana is a registered trademark of Tropicana Products, Inc.
Florida's Natural is a registered trademark of Florida's Natural Growers, a division of Citrus World, Inc.
Sources
This science project is based on:
Chem_p044_20140225.pdf
APE-5208-KIT