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I See! Vitamin C!

Mary Colvard

Data Sheet for Part One   Part Two   Teacher Notes

Part One

"Do different types of orange juice contain the same amount of vitamin C?"

Background

Have you had your daily requirement of vitamin C? If you ask most people that question, they will tell you they drank their orange juice or swallowed their vitamin C tablet. They probably won't tell you they ate their potatoes and broccoli! Also known as ascorbic acid, vitamin C is a biologically active agent found in many fruits and vegetables. Citrus fruits may be the best known, but are not the only significant sources of vitamin C.

Cells use some vitamins by changing them into molecules that combine with enzymes (organic catalysts) which control chemical activities. Without such vitamins, the enzyme molecules are not able to operate and the chemical reactions of the cell slow down. As the cell's functioning decreases, the metabolism and health of the whole organism is affected.

One important function of vitamin C is maintaining collagen--a protein necessary for the formation of connective tissue in the skin, ligaments and bones. Vitamin C also helps connective tissue form during the healing of wounds and in the growth and repair of tissues. Other functions of vitamin C include aiding in red blood cell formation, preventing hemorrhaging, and fighting bacterial infections. The human body cannot make and has a limited ability to store this chemical and it is therefore essential that it be ingested frequently.

Even though certain foods are known for their ability to provide us with vitamin C, a wide range of factors determines how much is actually available by the time you are ready to eat it. The vitamin C content in food is affected by the plant's growing conditions; method of processing; storage conditions; and exposure to heat, light or metals (especially iron, copper and aluminum).

Objectives

  1. To measure and compare the Vitamin C content in a variety of food samples.
  2. To determine the effect of various factors on Vitamin C concentration.

Materials

blender one stirring rod         Sources of Vitamin C
      -Freshly squeezed OJ
      -Bottled OJ
      -Frozen OJ
      -Canned OJ
vitamin C indicator solution graph paper
3 disposable pipettes distilled water
one 10-mL graduated cylinder cheese cloth
three 50-mL flasks or medicine cups      


Procedure

  1. Pour 15 mL of the vitamin C indicator into a 50-mL flask or medicine cup.

  2. Using a clean medicine dropper, add a drop of one of the orange juice samples to the indicator in the flask. Gently swirl the liquids to mix.

  3. Continue to add orange juice, drop by drop, until the indicator changes from blue to colorless.
    Note: Be sure to swirl after each drop is added.

  4. Observe and count the number of drops of orange juice you needed to add to the indicator to cause it to lose all of its color. Juices low in vitamin C will begin to dilute the indicator. The indicator will start to take on the color of the juice. If this occurs, indicate that no satisfactory end point was reached. Record the number of drops added in the chart on your data sheet.

  5. Repeat the above steps for each orange juice sample being tested.
    Note: Be sure to rinse your medicine droppers between tests and to use clean flasks for each trial!

  6. Test each juice three times and calculate the average number of drops (to the nearest tenth) required to change the indicator.

Data Sheet for Part One   Part Two   Teacher Notes


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