BEHS Chemistry

Assignment directions for a project measuring the amount of vitamin C in fresh squeezed fruit juice verses frozen concentrate 

Chem Projects Research Team

CheMystery Labs

380 South Buzz Blvd

Bee Hive, UT 84302

 

Dear Team:

 

The Citrus Growers of the county would like to know how the Vitamin C concentration in their fresh squeezed fruit juice compares to their frozen concentrate that has been mixed up according to the directions on the package. 

 

Some consumer groups have claimed that freezing destroys the Vitamin C in frozen fruit juices.  The Citrus Growers have a budget of $120,000 to answer their question.

 

 Before you begin your work, I will need the following information from you so that I can approve your work.  The planning space for these items is found in your project packet.

 

Ø       a detailed summary of your hypothesis, experimental

      design table, a plan for the procedures along with all

       necessary data tables

Ø       a description of necessary calculations

Ø       an itemized list of equipment with costs and chemical with

      their costs, include labor costs of $80 / hour and cost for

      laboratory space $10,000/day, and a standard disposal

      fee of $2000 / gram of material. 

 

After you complete the analysis, prepare a report for the Citrus Growers.  Remember that this report will be seen by a variety of people, so be certain it projects the image we want to present.  The items that should be included in the report are found in your project packet.

 

Good luck with the project.  Please keep in close contact me as you proceed with the project.  You will need a data verification signature, by having me observe one of the trials in the experiment.

 

Sincerely

 

Your teacher

 

President and CEO

CheMystery Labs Inc.

 

 

 

 

Vitamin C Analysis

                    One of the most interesting and fruitful applications of chemical knowledge in the last decade
           had been the development of food and nutritional chemistry.  The close link between diet and health
           and human behavior is now so firmly established that "we are what we eat" has almost become a cliché.
           Out of this explosion of information concerning the chemistry of nutrition have come many controversies,
           one of the most important of which is the problem of recommended dietary allowance (RDA).    The
           controversy has been very apparent (and at times bitter) with respect to the water soluble vitamins,
           especially vitamin C.  In the United States, the RDA for vitamin C is 60 mg for adults of both sexes.
           For children up to the age of 11 years, an allowance of 45 mg per day of vitamin C is recommended,
           and for older children 60 mg per day. The most famous proponent of the use of a much larger daily
           intake of vitamin C than the RDA is the two-time Nobel Prize winner Dr. Linus Pauling.  In his book
           Vitamin C and the Common Cold, Dr. Pauling has provided some cogent arguments that large doses
           (5 g daily) of vitamin C are beneficial to health.   The American Medical Association and the National
           Academy of Sciences keep insisting that there is no evidence for Dr. Pauling's claims.

                    Pure vitamin C (alternatively called ascorbic acid) is a white, crystalline organic compound with
           a chemical formula of C6H8O6 (F. Wt. 176.12 g mol -1).  The structure of ascorbic acid is usually
           drawn in one of the two following ways:

 

             Vitamin C is a weak acid that is very soluble in water (0.3 g mL-1).  One of the most important
           chemical properties of ascorbic acid, particularly with respect to its action as a vitamin, is that it is
           a reducing agent-i.e., it is relatively easily oxidized.  Pure, solid ascorbic acid can be stored for years
           without much change occurring.  However, in solution the vitamin can decompose rapidly due to
           oxidation by dissolved atmospheric oxygen.  The decomposition is accelerated by heat, light, alkalis,
           oxidative enzymes, and the presence of traces of iron and copper ions.  The oxidation is slowed down in
           an acidic medium and by cold temperatures

                Procedures:
 

                    This analysis for vitamin C is based on the chemical properties of ascorbic acid and iodine.
           Iodine (I2) solution is capable of oxidizing ascorbic acid, forming the colorless products
           dehydroascorbic acid, hydrogen ions (H+), and iodide ions (I-):

                        I2 (aq)   +    C6H8O6 (aq)  ----->      C6H6O6 (aq)   +               2 H+ (aq)    +      2 I- (aq)
                         Iodine        Ascorbic Acid              Dehydroascorbie           Hydrogen          Iodide
                                            (vitamin C)                          acid                            ion                        ion
 

                    You will perform a titration, a common procedure in chemical laboratories to determine
           concentrations or amounts of substances in solutions.  The general approach is to add known amounts
           of one reactant gradually from a buret to another reactant until enough for complete reaction has
           been added.  The point of complete reaction is observed by a color change or some other highly
           visible change that occurs at the endpoint of the reaction.  Knowing the reaction involved, the unknown
           amount of one reactant can be calculated from the known amount of the added reactant.

             The titration set up is illustrated below.

          WARNING:  DO NOT PUT IODINE IN A PLASTIC BURET, USE GLASS ONLY!!!
 

 


                           In this analysis, the endpoint is signaled by the reaction of iodine with starch suspension, which
           produces a blue-black product.  Starch is added to the beverage to be tested.  An iodine solution is
           slowly added from the buret.  As long as ascorbic acid is present, the iodine is quickly converted to
           iodide ion, and no blue-black iodine-starch color will be observed.  However, when all available ascorbic
           acid has been oxidized, the next drop of added iodine solution reacts with starch to form the expected
           blue-black color.  The endpoint in the titration, then, is the first sign of permanent blue-black color in the
           beverage-containing flask.
 
 
 
 
 
 
 
 

Part 1:

          STANDARDIZING the Iodine Solution

            1.  Dissolve a 250 mg Vitamin C (ascorbic acid) tablet in enough water to make 100 mL.
            2.  Measure 25 mL of the Vitamin C solution into a 125 mL Erlenmeyer flask.
            3.  Add 10 drops of 1% starch suspension.
            4.  Fill a clean buret with iodine solution.

WARNING:  DO NOT PUT IODINE IN A PLASTIC BURET, USE GLASS ONLY!!!





                 Record your starting buret volume.
            5.  Slowly add the iodine solution to the flask as you gently swirl the flask.  Continue until the
                 endpoint is reached (the first sign of blue color that remains after at least 20 seconds of
                 swirling).  A piece of white paper placed under the flask will help you see the endpoint.
            6.  Record your final volume.  Calculate the volume of iodine used in the titration.
            7.  Calculate the conversion factor.
                 a.  Calulate the number of mg of vitamin C in the 25 mL sample

                          25 mL  |   250 mg Vit C   =
                                     |   100  mL

                 b.  Divide the number of  mg of vitamin C by the volume (in milliters) of iodine solution
                      used in the titration..

                     ___ mg Vit C   =                       _______   mg Vit C
                            mL of Iodine                                        mL of Iodine
 

 

Part 2

ANALYZING FOR VITAMIN C IN YOUR SAMPLE

            1.  Measure 25 mL of the fresh squeezed fruit juice sample to be tested into a 125 mL Erlenmeyer
                 flask.
            2.  Add 10 drops of 1% starch suspension.
            3.  Fill a clean buret with iodine solution.  Record your starting buret volume.
            4.  Slowly add the iodine solution to the flask as you gently swirl the flask.  Continue until the
                 endpoint is reached (the first sign of blue color that remains after at least 20 seconds of
                 swirling).  A piece of white paper placed under the flask will help you see the endpoint.
            5.  Record your final volume.
            6.  Calculate the volume of iodine used in the titration.  Write the calculated volume of iodine
                 solution used in your data table.
            7.  Multiply the calculated volume of iodine used in each trial by the conversion factor
                 value from Part 1.  This calculation will give the number of mg of Vitamin C per 25 mL
                 of sample.
 
 
 
 
 
 
 
 

Other Ideas for Vitamin C Research Projects
 

 
 All the solutions and apparatus required for Vitamin C studies and analysis will be provided, except that you must provide the basic samples if you are going to analyze fruits, vegetables, and the like.  Here are some general suggestions for the types of projects that you might consider.

             o   Study some of the factors that are important in vitamin C decomposition, particularly Cu2+, Fe3+, heat and pH. 

                         This type of study could be done on pure vitamin C solutions or on fruit juices, etc.

    •  Determine the effects of various types of food preparation on vitamin C content.  A study on broccoli might include peeling, chopping, cutting, slicing, chipping, grating, micro-waving, boiling, steaming, etc.
    •  Dissect a fruit or vegetable and try to determine if there are any differences in Vitamin C content in various parts of the fruit or vegetable.  Core samples of, say, a potato might reveal cross-sectional vitamin C differences.
    •  Compare various brands of frozen or canned juices for vitamin C content.  Try to ascertain what factors determine the vitamin C content of a commercial juice.
    •  Compare the vitamin C content of various kinds of related vegetables - e.g., different kinds of peppers or different kinds of citrus fruit.
    • Study the factors that control the decomposition of vitamin C in stored fruit juices.  The variables you might look at are time, temperature, light, type of fruit, and pH.
    • Compare the vitamin C content of different breakfast cereals, particularly with respect to any claims made on the packet about RDA percentages.


     NOTE:  The projects outlined above are merely suggestions.  You are encouraged to design your
                 own investigation.  If you need any help, please discuss it with your instructor.

Contact: Tom Davidson, Box Elder High School 380 So. 600 w. (435-734-4840) Email: tom.davidson@besd.net