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Vitamins In Your Juice

based on 6 ratings
Author: Muriel Gerhard

Grade Level: 8th - 9th; Type: Chemistry

Objective:

Identify vitamin C in fruit juices and to determine which of the following juices contain the most vitamin C, orange, apple, cranberry or grape

Research Questions:

  • What is ascorbic acid?
  • How is ascorbic acid used by the human body?
  • What is an indicator?
  • How is iodine used as an indicator?
  • How does titration assist us in quantifying our data?
  • What happens during an oxidation/reduction reaction?

On the information level, this experiment serves to acquaint students with basic Information on how to determine the amount of ascorbic acid, another name for vitamin C, in various fruit juices namely orange, apple, cranberry and grape. The human body is incapable of producing vitamin C and is therefore dependent on obtaining this vitamin from food. Since this is a quantitative study, it would be ideal to use the titration method. Titration enables us tomeasure the unknown amount of a chemical in a solution.  It reacts with the titrant (the unknown solution) and enables us to calculate the concentration from the amount of titrating solution which we added and the proportion or the ratio of the two chemicals in the chemical reaction.

In this experiment, the student will titrate vitamin C (ascorbic acid) by using iodine. He/she use an oxidation /reduction reaction.  The ascorbic acid is oxidized and the iodine is reduced to iodine ions. The student starts with a known concentration of iodine and carefully measures the amount being added. He/she can readily calculate how much vitamin C is present. Color changes such as when iodine comes in contact with starch and the solution and starch turn blue black, serve to alert us as to when all of the ascorbic acid has been oxidized. Once all of the ascorbic acid is oxidized, added iodine will alert us by reacting with the starch and turning blue black. 

This science fair experiment also serves to acquaint students with the essential processes of  using the scientific method, of clearly delineating the project`s objective, of formulating a hypothesis as to the anticipated outcomes of the project as well as recording and analyzing, synthesizing  data and formulating  valid results within the parameters of the obtained data.

Materials:

  • Cheesecloth
  • Vitamin C  tablets
  • Distilled water
  • Transfer pipettes
  • Masking tape
  • Permanent marker
  • Small funnel
  • Lugol's iodine solution
  • Soluble starch
  • 50 mL graduated cylinder
  • 250 mL  graduated cylinder
  • 500 mL  graduated cylinder
  • 50 mL  Ehrlenmeyer flask
  • 50 mL  buret ring stand
  • Electronic kitchen balance (accurate to 0.1 g)
  • Glass jars for iodine (300 mL)
  • Starch solutions
  • Orange, apple, cranberry and grape juices.

All of these can be purchased from Science Kit and some of the materials may be borrowed from the school science lab.

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