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Experiment #1
Investigating Chromatography with Skittles and M&M’s
Purpose
To determine if Skittles
and M&Ms of the same color, contain the same dyes.
Pre-lab
On your lab report, RE-TYPE
each of the following questions followed by your answer. Note sources used as a bibliography will be required.
1. What is the purpose of
chromatography?
2. What is the difference
between the mobile and stationary phases.
3. What is the retention
factor, Rf, and how is it calculated?
4. Four main types of chromatography
include paper chromatography, gas chromatography, thin-layer chromatography, and column chromatography. For each type, indicate
the mobile and stationary phase and a practical application. Include sketches or diagrams as needed.
5. In paper chromatography,
what determines how far a particular molecule travels up the paper i.e. what factor(s) affect the Rf value for a particular
substance?
6. Why are dyes added to
food? Provide a minimum of 3 reasons.
7. List 6 dyes (such as yellow
#6), their chemical name and foods where they are commonly used. Include the structural formula of at least 3 of the dyes.
8. Find 5 household products
around the house that list one or more dyes in their ingredients. Identify the product and associated dyes.
Materials
6 Skittles and
6 M&Ms of 3 different colors (2 of each color such as 2 red of each, 2 orange of each and 2 green of each) NOTE:
All students much use green as one of their colors.
2 saucers
6 pieces of chromatrography
paper (from teacher)
2 tall glasses
ruler
6 capillary tubes (from teacher)
opened paper clip
Hypothesis
State whether or not you
think the chromatogram of the same color of Skittles and M&M’s will be the same or different. Include a reason for
your hypothesis.
Procedure (For Green Skittles and M&Ms)
1. Cut two pieces of chromatography
paper so they are about 1 cm taller than the glass you will be using.
2. Draw a pencil line horizontally
across the paper, 2 cm from the bottom. Below the line put an S for Skittles and on the other line put an M for M&Ms.
3. Make a pencil dot in the
center of the line.
4. Take two green Skittles
and place them on the saucer. Add a few drops of water and move the Skittles around in the water until some of the dye has
dissolved into the water. Remove the candy.
5. Repeat this step with
the green M&Ms in the other saucer.
6. Touch the capillary tube
to the solution containing the Skittles dye. Then transfer the solution to the corresponding spot on the strip of chromatography
paper marked “S”. Allow the spot to dry and add some more. Do this 3 times or until the color is strong.
7. Repeat step 6 with the
green M&M dye on the paper marked “M”.
8. Add 1 cm of water to the
glass.
9. Put the opened paper clip
through the top of the paper.
10. Lower the chromatography
paper into the center of the glass until it touches the water. Make sure the water does not go above the pencil line on the
paper. Rest the opened paper clip across the top of the glass so the paper is suspended in the middle and not leaning against
the side of the glass.
11. Observe the dyes until
the water has almost reached the top of the chromatography paper. Record observations as you watch the dye(s) move up the
paper.
12. Remove the chromatography
paper and allow it to dry.
13. Sketch the papers using
colored pencils to show the locations of the dyes and a line to show how high the solvent traveled. Label the sketches appropriately.
14. Measure and record the
distances traveled by any dyes as well as the distance traveled by the solvent (in cm).
15. Save the chromatography paper and attach it to your lab report.
16. Repeat this procedure for the other two colors of candy you have chosen.
Post-Lab
On your lab report, RE-TYPE
each of the following questions followed by your answer.
1. What colors were the candies
that you used?
2. Record your observations
and sketch the papers indicating the location of various colors using appropriate colored pencils.
3. Calculate the Rf
factor for each dye in each candy. (Include all work. Watch units and sig figs)
4. Identify the mobile and
stationary phases in your experiment.
5. Why did different dyes
travel different distances on the paper? (What is different about them that affects the distance they travel?)
6. Did each color of Skittles
and M&Ms contain the same dyes? How could you tell?
7. Were any of the colors
actually composed of two or more dyes? If so, which one(s) and how could you tell?
8. Compare your results with
your hypothesis.
Lab Report
Title
Purpose
Answers to Pre-lab questions
Summarize the procedure used
using paragraph form, in past tense and passive voice
Hypothesis including explanation
Observations while the experiment
was running
Data Table
Sketches (labeled) of 6 chromatograms
(Identify each such as red Skittles)
Answers to Post-lab questions
Bibliography (Using correct
MLA format)
Chromatogram attached
