Vitamin C is required for good health. This vitamin is not produced by your body and must be obtained from foods or vitamin tablets.
aksiografi.com – Food is the body’s fuel for energy production. In the human body there are biochemical reactions because there are calories as biochemical energy in food. Vitamin C is required for good health. This vitamin is not produced by your body and must be obtained from foods or vitamin tablets.
In this project, you will use the titration method to determine the amount of vitamin C in various foods and its tablets. You will also determine whether fruit drinks and fruit juices have comparable amounts of this vitamin. Vitamin C’s antioxidant properties will be studied, and its part in an oxidationreduction reaction will be examined. You will also look at the sources and uses of different vitamins.
To determine the amount of iodine needed to react with a standard solution (carefully measured quantity) of vitamin C.
CAUTION: Be careful not to allow the vitamin C to touch your skin, in case you have any sensitivity to the chemical.
100-mg ascorbic acid (vitamin C) tablet
½ cup (125 ml) of distilled water
1-quart (1-liter) jar
4 baby-food jars
1-teaspoon (5-ml) measuring spoon
starch solution (see Appendix 5)
sheet of white paper
tincture of iodine
CAUTION: Keep the iodine out of reach of small children. It is poisonous and is for external use only. 1. Prepare a standard vitamin C solution by: • crushing the tablet (place it between two sheets of wax paper and hit it gently with a hammer). • pouring ½ cup (125 ml) of distilled water into the quart (liter) jar. • adding the crushed vitamin C powder to the water in the jar. • stirring until the powder dissolves.
2. Pour equal portions of the standard vitamin C solution into four baby-food jars.
3. With the marking pen, write ”A,” “B,” “C,” and “D” on pieces of masking tape and tape one label to each jar.
4. Add 1 teaspoon (5 ml) of the starch solution to each jar.
5. Place jar A on the sheet of white paper.
6. Fill the eyedropper with tincture of iodine. Slowly add the iodine in the eyedropper to jar A, counting each drop added (see Figure above). Swirl the jar after each addition of five drops. Continue to add the iodine until the jar’s contents remain a blue-black color.
7. Record the number of drops required to turn the jar’s contents this blue-black color.
8. Repeat the procedure using jars B, C, and D.
9. Add the results for the four jars and divide by four to compute the average number of drops of iodine needed to react with the 25 mg of vitamin C in each jar. Note: This number will be used to calculate the concentration of it in other substances.
Results of Testing Food
The vitamin C-starch solution is unaffected by the initial drops of iodine, but adding more iodine results in a blue-black solution. Note: The number of drops of iodine needed to react with the 25 mg of this vitamin in the solution will vary with the size of the eyedropper.
Titration is the process of combining a measured amount of a solution of known concentration with a measured amount of solution of unknown concentration. Tincture of iodine is a mixture of elemental iodine (I2) and ethyl alcohol (C2H5OH). The combination of elemental iodine and vitamin C chemically changes it (ascorbic acid) to a compound ineffective as a vitamin called dehydroascorbic acid. The elemental iodine is changed to a charged particle called iodide (I- ).
Elemental iodine reacts with starch to produce a blue-black color, but mixing the charged particle iodide with starch does not produce a color change. When starch, vitamin C, and elemental iodine are mixed, the iodine is more attracted to the vitamin C molecules. The starch stays in the solution unchanged until all of the vitamin C has combined with the elemental iodine. When the last molecule of vitamin C reacts with the iodine, then the starch molecules combine with any remaining iodine, producing a starch-and-iodine, blue-black-colored complex molecule.
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