; Chromatography of Food Dyes Answ
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Chromatography of Food Dyes Answ

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									                Sample Answer Key
                Lab Report: Chromatography of Food Dyes
                Name of Course:    AP Chemistry
                Instructor’s Name: [Enter name here]
                Date:              [MM/DD/YYYY]
                Student Name:      [Your Name]

Note: This is a ‘wet lab.’ Students complete this lab home. Therefore, data will vary.
Briefly discuss the background necessary to understand the theories and objectives involved in the
experiment. Include all pertinent chemical reactions, using subscripts and superscripts where appropriate.
This should be written in present tense, narrative style.

Paper chromatography is a technique for separating a mixture. The mobile phase (a solvent & a
substance being tested) is applied to the stationary phase (paper) and a pattern of separated
colors appears. Each component travels at a different rate of speed and a different distance.
Measurements taken of the lines of color tell us something about the substance. The location of
the compound on the stationary phase is indicated by an Rf value, where:

There are at least 6 different FD&C food dyes present in the samples you will use in this lab: Blue #1,
Blue #2, Red #3, Red #40, Yellow #5, & Yellow #6. Based on this information, predict what dyes you
think are present in each of the following: red food coloring, blue food coloring, yellow food coloring,
green food coloring, each of the different colors of M&M’s in your bag, strawberry Kool-Aid, grape Kool-
Aid and unknown mixtures of dye. Give your reasons and outline any assumptions that lead you to this

Hypothesis will vary. Sample hypothesis:

Strawberry Kool-Aid contains sone type of just red dye.

Grape kool-aid contains one of the blues and one of the reds.

The green M & M’s have blue #2 & yellow #6.

The hypothesis is based on the fact that the strawberry kool-aid is red.

For the grape kool-aid, red and blue make purple.

For the M & M’s, yellow & blue make green, so it makes sense that the green M & M’s are
comprised of blue and yellow food coloring.
Materials and Methods
Write a brief paragraph, in past tense, describing the methods used to conduct the experiment. Use the
checklist at the end of the instruction found in this link to ensure all aspects of this section are included.

The colored substances were put on marked chromatography paper with a toothpick. The paper
was put in salt water so the fronts could move. The tops of the solvent fronts were marked and
the paper was allowed to dry. Heights of the dye & solvent fronts were measured.

Create a table to record the heights of the dye and solvent-front in each column. Present data neatly,
with clear labels & units.

The sample data presented should be typical for results that can be expected,
but results will vary from student to student.

   Color     Blue1 Blue2 Red3 Red40 Yellow5 Yellow6 Solvent
 Distance 35         3      11     24       41         32         60
 Rf          .58     .05    .18    .4       .68        .53
This data above was not collected or viewed by the student but is here for
instructor reference only.

In the following tables, if there are two distances, it is because there were two
colors that separated. The color and the respective distances are listed.
     Substance           Kool-Aid®:            Kool-Aid®:          Solvent
                             Grape             Strawberry
 Distance (mm)        Red: 6              9                       60
 Distance (mm)        Blue: 19
 Rf                   .1 & .32            .15

   Substance            Store           Store             Store            Store          Solvent
                         Red           Yellow             Green             Blue
 Distance (mm)         53            60                Yellow: 51        Red: 33         81
                                                       Blue: 73          Blue: 72
 Rf                    .65           .74               .63 & .9          .41 & .89

    Substance            M&M    M&M               M&M           M&M         Solvent
                        Green Yellow              Blue          Red
 Distance (mm)          10    31                51             9            81
 Rf                     .12   .38               .63            .11

The unknown changes on a regular basis, but should be easily identified from the
data tables.
Calculate and record in a table the Rf value for the dyes for each spot. Show one sample calculation for
calculating Rf. Analyze the data you collected in the lab by preparing a graph or a table which compares
the Rf values for the different dyes in preparation for your discussion in the next session.

See Rf values in data table above. The student should record them here.

Discussion and Conclusion
After conducting the experiment, answer the five questions below in complete and reflective sentences.
Consider whether your conclusion is the only explanation for the data you collected, or if there could be
alternate explanations. Troubleshoot your data and mention limitations to the methods used and how this
may impact the data.

    1. What are three potential sources of error specific to this lab and how may they
       have affected your results? How could the margin of error for this experiment
       have been further reduced?
           Forgetting to mark the solvent front before it stopped
           Salt solution was too concentrated or weak; would cause the
              solvent to run differently.
           Dye fronts are difficult to see/measure, measuring incorrectly;
              wrong values.

               The margin of error can be reduced by performing three trials and
                paying close attention to the solvent front.

    2. The ink pen you write with contains several different colors of dye. Write a brief
       procedure which would allow you to purify and concentrate all of the yellow dye
       in your ink sample. You must use paper chromatography as part of your
       procedure. When you are finished, you should have a pure sample of yellow dye
       as a final product. The other dyes do not have to be saved or purified.

        You could do paper chromatography to separate the dyes in the ink. Then
        you could cut out all the paper with the yellow dye on it, soak it in a solvent
        to remove it from the paper and then evaporate the solvent.
3. You run a chromatogram of two different food colors, each consisting of a single
   substance. One food color (spot X) has an Rf of 0.350; the other (spot Y) has an
   Rf of 0.750. Using the drawing toolbar, draw a sketch of the chromatogram.
   Include in your sketch: the origin, the solvent front, and the two labeled spots
   (label all parts).

   Origin is dotted line. Black lines are solvent fronts. Red line is spot Y,
   Green line is spot X.
4. Two extreme values for Rf are 1 and 0. Explain what each value means in terms
   of the compound's affinity for the paper versus the eluting solution.

   An Rf of 1 would mean that the mobile phase was primarily pure solvent.
   The solutes did not slow down the solvent front. An Rf of 0 means that the
   mobile phase was not mobile on the stationary phase.

5. Discuss if the hypotheses for the experiment was supported or refuted. Be sure to
   reference all of the results from the lab in your discussion. Keep in mind that you
   will not be able to determine the exact dyes in the samples. However you should
   be able to include which sample contain a particular blue, red or yellow dye. You
   can give them the names, Blue #1, Blue #2, Red #3, Red #40, Yellow #5, &
   Yellow #6. Or make up names of your own for ease of communication. If you
   conclude that there are additional dyes present, explain why you came to that
   Answers will vary but should be well supported. Sample answer based on
   hypothesis above:

        The hypothesis was supported. The rf values matched those
   determined in the lab.

   Strawberry Kool-aid had only red and it had an rf value of .15 which is
   close to that expected for Red #3 (.18). Grape kool-aid separated into just
   a red and a blue. The green M & M’s only separated into the blue, though
   it was expected to have yellow as well.

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