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Vitamin C Investigation
Resources
Extraordinary or unique resources (human or material) needed to successfully complete this experience:
Number Five graphic

Materials needed for the lab were simple and inexpensive. Each group of two students required:

  • vitamin C indicator solution
  • three 50 mL beakers or medicine cups
  • one 10 mL graduated cylinder
  • three disposable pipettes
  • one stirring rod
  • Sources of Vitamin C: freshly squeezed OJ, bottled OJ, frozen OJ, canned OJ
  • Optional: container for waste solutions and source of clean rinse water

There are two different preparations (starch-iodine or indophenol) that may be used for the vitamin C indicator solution. Neither is more accurate than the other. The starch-iodine mixture is much cheaper. It can be made ahead and stored in a dark, cool place in two liter soda bottles and dispensed in liter containers at the lab stations. Both indicators vary from one preparation to the next; so an accurate measure of vitamin C is not really possible with this protocol. The results allow students to compare relative amounts of vitamin C present.

Starch-Iodine

  • Add 2 g of cornstarch or potato starch in 200 mL of cold, distilled water. Bring the mixture to a full boil in a glass beaker.
  • To 1 liter of water, add 8 mL of the starch solution and 1 mL of tincture of iodine.
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    Note: Specific amounts are given here but variations that produce a royal blue color of the starch/iodine indicator may also be used. The color of the starch indicator should be a royal blue. Just before doing the lab, check the indicator and dilute the concentration so that a workable number of drops of fresh orange juice (5 to 25) turn the indicator colorless.

    Tincture of Iodine

  • Add 2 g of Iodine crystals to 45 mL of ethanol and dissolve.
  • Dissolve this mixture in 55 mL of distilled water.
  • Add 2.4 grams of KI to this mixture and dissolve.
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    Indophenol

  • Stock solution: dissolve 100 mg of 2,6 dichloro-indophenol salt in 100 mL of distilled water.
  • Prepare a working solution by diluting the stock solution at a 1:10 ratio with distilled water.
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    Students must also have access to computers. This included the computer lab, the library, classroom, and home settings. Computer access was necessary since they were required to access the Internet and find vitamin/enzyme information. They also were required to word process their lab reports for Part B of the Vitamin C Analysis. For students presenting their material via a computer slide show, they had to have a working knowledge of ClarisWorks or PowerPoint.

    The slide shows were also printed out. In some instances glossy pictures were made of some of the nicer digitized images and drawings. To be able to do the slide show part of the activity, students needed: computers, Internet access, a means of projecting the slide shows so that they could be seen on a large monitor or the overhead projection screen, disks, perhaps a zip drive and zip disks (since some of the slide shows became quite large), glossy paper, a color printer, and transparencies.

    Part A of the Student Analysis

    Performance Assessment

    Scoring Guides and Rubrics

    Scoring Guide for Laboratory Report

    Scoring Guide for Lab Performance

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