Extraordinary or unique resources (human or material) needed to successfully complete this experience:
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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.
# 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.
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.
# Stock solution: dissolve 100 mg of 2,6...
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