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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. Introduction 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: Hypothesis 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. 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. Observations/Data 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 (mm) 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. Analysis 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 conclusion. 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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