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Do oranges lose or gain vitamin c when picked?

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Christian Vertiz

on 18 May 2015

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Transcript of Do oranges lose or gain vitamin c when picked?

Christian Vertiz, Jesus De La Torre
Do oranges lose or gain vitamin c when picked?
In this project you will learn a method for determining the amount of vitamin C in a
solution. The technique you will be using is called titration. Titration is used to determine the
unknown concentration of a chemical in a solution. The added chemicals reacts with the original
chemical, whose concentration is unknown. The original chemical is called the titrant, and the
added chemical whose concentration is known is called the titration solution. The titration
solution reacts with the titrant, and the progress of this reaction is carefully monitored. When
100% of the original compound has reacted with the added chemical, the concentration of the
original chemical can be determine from the amount of titration solution that was added. To have
a better understanding how a titration works, let us look at the specific example of determining
the concentration of vitamin C. Vitamin C also known as ascorbic acid, is the titrant in this case
because it is unknown. You start with a measured volume of the titrant. The titrating solution that
will added to the titrant is iodine. You will start out by using your iodine solution to titrate a
known amount of vitamin C, using a solution prepared from a vitamin C tablet. You will
carefully measure the amount of iodine solution needed to titrate the known amount of vitamin
C. You will know when the titration is complete because you will add a third chemical-soluble
starch-to the solution. The starch acts as an indicator: the starch changes the color of the solutionWhen iodine/ vitamin C reaction is complete. As soon as the solution changes color, you will stop \adding iodine solution. Once you have calibrated your iodine solution with a known amount of vitamin C, you can then repeat the procedure to determine how much vitamin C there is in
samples of fresh-squeezed orange juice. The chemical reaction of iodine with vitamin C is called
an oxidation-reduction reaction (chemist often use the shorthand ‘redox reaction’ to refer to this
type of reaction). 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 I oxidized, and the molecule that accepts the electrons is reduced.
In this chemistry science project, you will investigate how different storages times affect the
amount of vitamin C in fresh-squeezed orange juice. How do you think the amount of vitamin C
will change at all? Get ready to do some titration to find out for yourself.
1. What happens when iodine added to a starch solution?

2. What happens when iodine is added to starch solution that also contains vitamin c?

Research Questions

1. I think that oranges that are picked up don’t lose nor gain vitamin C after being picked.

2. I think that oranges do lose vitamin C after being picked.

3. I think that oranges gain vitamin C after being picked.
Orange Juice Titration Kit. Includes:,Cheesecloth Vitamin C tablets, 250 mg each,Chemical splash goggles
2% Lugol's iodine solution (30 mL); also available from Amazon.com
Consult the iodine Materials Safety Data Sheet for additional safety information.
Soluble starch (30 g)
Small funnel. Do not use the funnel for food after using it for chemistry.
50 mL graduated cylinder,500 mL graduated cylinder,50 mL Erlenmeyer flask,50 mL buret,Ring stand,
Buret clamp,Lab apron,
Eyedropper. A transfer pipette or medicine dropper would work, too.
Nitrile gloves. Rubber or latex gloves would work, too.
Measuring spoons. A balance accurate to the 0.1 gram would also work.
100 mL beaker
Glass bottles, amber, 8 oz (2). Iodine is light-sensitive and needs to be stored, once mixed, in an amber glass bottle or in an aluminum foil-covered bottle.
You will also need to gather these items:
Optional: Newspaper to protect the surface you work on
Stovetop,A cooking pot,Stirrer
Clean glass jar with a lid for storing the starch solution, Cutting board,Knife,Bowl,Masking tape,Permanent marker,
Juicing oranges or other citrus fruit (at least 15 fruits of the same type),
Ideally, you would have access to a citrus tree with ripe fruit.
The next-best option is to use a big batch of store-bought citrus fruit.
You will get better juice yield if you use juicing oranges, such as Navel oranges or Valencia oranges, not eating oranges. You may need to do a little research to determine if the oranges are typically used for juicing.
Juicer for extracting juice from oranges
Distilled water; available in the bottled water section of most grocery stores
Lab notebook
Project Rational
Risks and Safety
Adult supervision required. Concentrated iodine is poisonous if swallowed.
Learn more here: http://www.hometrainingtools.com/media/reference/CH-IODINE.pdf

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. Make a starch indicator solution. This can be anywhere from 0.5 to 1.0%. The exact amount of starch is not critical.
4. 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
5. Set up the 50 mL buret on the ring stand.
6. Titrate 20 mL of vitamin C standard solution.
7. Prepare fresh-squeezed orange juice for testing. You will want to prepare samples so that you can measure the vitamin C content of at least three oranges on the day of picking (day 1) and on days 3, 7, 14, and 21 (after picking).
8. Titrate the fresh-squeezed orange juice you just prepared by repeating step 7, but this time, use 20 mL of fresh-squeezed orange juice in the Erlenmeyer flask instead of 20 mL of the vitamin C solution
9. When you collect your other fresh-squeezed orange juice samples (on the days described in step 8), titrate each sample by repeating step 9. Be sure to make a fresh vitamin C standard solution on each day that you measure the vitamin C in your orange juice samples.
10. For each time point (day 0, day 3, day 7, day 14, and day 21), calculate the average amount of iodine needed to titrate the 20 mL sample. Record your results in your lab notebook.
11. Calculate the amount of vitamin C in your samples by setting up a proportion, as shown in Equation 1. You will want to solve for Vitamin C2
12. Graph your results, putting the time points on the x-axis and the average amount of vitamin C on the y-axis.
13. Analyze your results.

Home Science Tools. (n.d.). Material Safety Data Sheet: Iodine Potassium Iodide Solution. Home Training Tools, Ltd. Retrieved November 3, 2013, from 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
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

Next time we can compare different storage methods for juice oranges. Like what effect does refrigerated storage have on vitamin C levels? Is refrigeration better at preserving vitamin C than room-temperature storage?
Future Studies
In conclusion the oranges lose Vitamin C - due it being unstable to oxygen, light and temperature. One of our hypothesis was correct because oranges did lose vitamin C.
Oranges do end up losing vitamin C because they stop receving the nutrients they need when picked up.
Data Analysis
The oranges keeps losing vitamin c after they being picked up.
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