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Which Orange Juice Has the Most Vitamin C?
Transcript of Which Orange Juice Has the Most Vitamin C?
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's 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.
The purpose of this experiment is to determine which orange juice has the most vitamin c: home-made fresh-squeezed, premium not-of-concentrate, or frozen made from concentrate.
If the orange juice is premium, then it will have the most vitamin c because during pasteurization, vitamin c is added.
•Orange Juice Titration Kit (1). Includes: ◦Juicer for extracting juice from oranges
◦Vitamin C tablets, 250-mg
◦Chemical splash goggles
◦2% Lugol's iodine solution (30 mL); also available from Amazon.com
◦Soluble starch (30 g)
◦Small funnel (do not use for food after using it for chemistry)
◦50 mL graduated cylinder
◦500 mL graduated cylinder
◦50 mL Ehrlenmeyer flask
◦50 mL burette
◦Eyedropper (a transfer pipette or medicine dropper would work too)
◦Nitrile gloves (rubber or latex would work too)
◦Measuring spoons (a balance accurate to the 0.1 gram would also work)
◦100 mL beaker
◦Glass bottle, amber. Iodine is light sensitive and needs to be stored, once mixed, in an amber glass bottle or in an aluminum foil covered bottle.
Dilute the Lugol's solution 1:10 in distilled water to make your iodine titration solution. a. Pour the 30 mL Lugol's solution into the 500 mL graduated cylinder.
b. Add enough distilled water to bring the total fluid volume to 300 mL and mix.
c. Store the solution in a clean, tightly covered glass jar that is clearly labeled. Store it in a location that is protected from light.
d.Rinse and dry the 500 mL graduated cylinder.
Make a starch indicator solution. a. This can be anywhere from 0.5 to 1.0%. The exact amount of starch is not critical.
b. For a 0.5% solution, add 1 g (which is equivalent to 1/4 teaspoon) of soluble starch to 200 mL of near-boiling distilled water.
c. Stir to dissolve, and allow to cool.
d. When cool, store the starch solution in a clean, tightly covered glass jar that is clearly labeled.
e. Rinse and dry the 500 mL graduated cylinder.
Make a fresh vitamin C standard solution (1 mg/mL). Do this on each day that you make vitamin C measurements from orange juice. 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 juice from oranges.
b. Crush a 250 mg vitamin C tablet, and dissolve it in 100 mL of distilled water.
c. Pour into a graduated cylinder and add distilled water to bring the total volume to 250 mL.
Control-the amount of orange juice
Variables- type of orange juice, amount of vitamin c
Independent Variable: type of orange juice
Depedent Variable: amount of vitamin c
The data that I will collect in this experiment is how many droplets of iodine does it take for the orange juice to change color(titrate).
•Samples of three different kinds of orange juice: ◦ Home-made fresh-squeezed (which means you'll need to buy some oranges)
◦ Premium not-from-concentrate juice (e.g. Tropicana® or Florida's Natural®)
◦ Made from frozen concentrate (following instructions on the concentrate can)
•Distilled water; available in the bottled water section of most grocery stores
Titrate 25 mL of vitamin C standard solution. a. Use a clean 50 mL graduated cylinder to measure 20 mL of vitamin C standard solution.
b. Pour this into a 50 mL Ehrlenmeyer flask (the shape of this flask allows you to swirl the solution to mix it without spilling).
c. Add 10 drops of starch indicator solution.
d. Set up the 50 mL buret on the the ringstand.
e. Use a funnel to carefully fill the buret with your iodine titration solution. Tip: the fluid level should not be past the graduated markings on the buret.
f. Write down the initial volume of the iodine titration solution in the buret.
g. Place the Ehrlenmeyer flask (containing the vitamin C and starch solutions) under the buret.
h. Carefully release the spring clamp of the buret to add iodine solution drop by drop.
i. Swirl the flask to mix in the iodine solution after each addition.
j. The titration is complete when the iodine creates a blue-back color in the solution that lasts for longer than 20 seconds.
k. Record the final volume of the iodine solution in the buret.
l. The difference between the initial volume and the final volume is the amount of iodine titration solution needed to oxidize the vitamin C.
m. Repeat this step three times. You should get results that agree within about 0.1 mL.
Here's how to prepare fresh-squeezed orange for testing. a. Use a juicer to squeeze orange juice from two (or more) oranges.
b. You need 20 mL of juice per titration, and you should do at least three titrations per storage condition, for a total of 60 mL.
c. Filter the orange juice through cheesecloth to remove any pulp and seeds.
Titrating an orange juice sample is quite similar to titrating the vitamin C standard. Here are the steps: a. Tip: if any of the orange juice samples contain pulp, filter them through clean cheesecloth before doing the titration.
b. Use a clean 50 mL graduated cylinder to measure 20 mL of the fresh-squeezed juice.
c. Pour this into a 50 mL Ehrlenmeyer flask (the shape of this flask allows you to swirl the solution to mix it without spilling).
d. Add 10 drops of starch indicator solution.
e. Set up the 50 mL buret on the the ringstand.
f. Fill the buret nearly full with your iodine titration solution.
g. Write down the initial volume of the iodine titration solution in the buret.
h. Place the Ehrlenmeyer flask (containing the vitamin C and starch solutions) under the buret.
i. Carefully release the spring clamp of the buret to add iodine solution drop by drop.
j. Swirl the flask to mix in the iodine solution after each addition.
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. If you continue to add iodine, the color will darken further. You want to note the volume of iodine added when the color first changes.
l. Record the final volume of the iodine solution in the buret.
m. The difference between the initial volume and the final volume is the amount of iodine titration solution needed to oxidize the vitamin C.
n. Repeat this step three times. You should get results that agree within about 0.1 mL.
For each juice (fresh, premium, or from-concentrate), calculate the average amount of iodine needed to titrate a 20 mL sample.
You can calculate the amount vitamin C in your samples by setting up a proportion
Summary and Conclusion
My hypothesis was rejected. Even though in premium orange juice vitamin c is added during pasteurization, freshly squeezed orange juice still has more vitamin c than premuim and frozen orange juice. The results of each trial mean the orange juice with the highest amount of droplets then that orange juice is the orange juice with the most vitamin c. The results answered my topic question because we were trying to determine which orange juice had the most vitamin c and by doing this experiment we were able to conclude that home-made fresh-squeeze orange juice has the most vitamin c.
You can apply this to the real world because if you are trying to increase your vitamin c intake and you want to know which type of orange juice would has the most amount of vitamin c.
I would like to thank my mom for buying the materials I need and taking the pictures of me doing the experiment.
University of Canterbury, n.d. "Determination of vitamin C Concentration by Titration," Science Outreach Programme, College of Science, University of Canterbury, Christchurch, New Zealand [accessed July 18, 2007] http://www.outreach.canterbury.ac.nz/chemistry/documents/vitaminc_iodine.pdf, and
Ganong, B., n.d. "Determination of Vitamin C in Orange Juice," Mansfield University [accessed July 18, 2007] http://faculty.mansfield.edu/bganong/biochemistry/vitaminc.htm.
Forest Park High School
Orange Juice Trial 1 Trial 2 Trial 3
Fresh. 61 64 65
Premium. 33 36 37
Frozen. 35 38 39
How many droplets of iodine does it take to titrate different types of orange juice?