Chemistry
Name: _____________________________________
Period: _______
Lab Partners: ______________________________________
Candy Chromatography
Objectives



To isolate dyes from candies
To separate the components of dyes in various candies
To compare the composition of dyes used in different brands of the same color of candy
Materials Needed
Equipment
 400-mL beaker
 Hot plate
 Four medium test tubes
 15-cm piece of woolen yarn (pale in
color)
 Stirring rod
 Red litmus paper
 Evaporating dish
 Scrap strip of chromatography paper
 Capillary tubes
 Sheet of chromatography paper, 20
cm x 20 cm
 Pencil
 Ruler
 Stapler
 600 mL beaker
 Plastic food wrap
Chemicals
 Candy (14 oz bags of M&Ms and
Skittles)
 Vinegar
 1.0 M ammonia solution
 Standard solutions for all colors
represented in candies used
 FD&C food dyes
Discussion
Many items, from clothing to food, are dyed with chemical dyes that contain a combination of
pigments. In this experiment, you will use paper chromatography to separate into components
the dyes used in M&M and Skittles candy. You will then compare these components against
food color standards.
Chromatography is a separation technique that takes advantage of differences in the
affinities the various components of a mixture have different mediums. For all types of
chromatography, there are at least two mediums in different phases—one that is called the
stationary phase, often a solid or a liquid, and this is the phase that does not move. The other
phase is called the mobile phase, often a liquid or a gas, and this phase moves through the
stationary phase. The mobile phase is the solvent.
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Candy Chromatography Lab
In paper chromatography, paper is the stationary phase. The mixture to be separated is
spotted onto the paper, and the paper is placed upright in a liquid solvent, as shown in Figure 1.
The solvent is allowed to travel up the paper, meaning that in this case the mobile phase is a
liquid. The components of the mixture move various distances up the paper. In general, the
greater affinity a component has for a liquid, the faster that component travels along with the
liquid. Conversely, the greater the affinity a component has for the stationary paper, the slower
it travels along with the liquid. The components of a mixture can therefore be separated from
one another as they travel along with the solvent at different rates. This process results in a
series of dots known as a chromatogram. A sample is shown in Figure 2.
As the solvent rises to the level at which the spot of mixture was applied, various effects can
occur, depending on the constituents of the spot. Those components of the spot that are
completely soluble in the solvent will be swept along with the solvent front as it continues to
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Candy Chromatography Lab
rise. Those components that are not at all soluble in the solvent will be left behind at the original
location of the spot. Most components of the unknown spot mixture behave in an intermediate
manner as the solvent front passes. Components in the spot that are somewhat soluble in the
solvent will be swept along by the solvent front, but to different extents, reflecting their specific
solubility and specific affinities for the paper. By this means, the original spot of mixture is
spread out into series of spots or bands, with each spot or band representing one single
component of the original mixture.
The separation of a mixture by chromatography is not solely a function of the solubility
of the components in the solvent used, however. The chromatography paper used in
chromatography is not inert but rather, consists of molecules that may interact with the
molecules of the components of the mixture being separated. Each component of the mixture is
likely to have a different extent of interaction with the chromatography paper. This differing
extent of interaction between the components of a mixture and the molecules of the support
forms an equally important basis for the separation. Chromatography paper adsorbs molecules
on its surface to differing extents, depending on the structure and properties of the molecules
involved. To place a paper chromatography on a quantitative basis, a mathematical function
called the retention factor, Rf , is defined:
Rf = distance traveled by spot / distance traveled by solvent front
The retention factor depends on what solvent is used for the separation and on the specific
composition of the chromatography paper or slide coating used for a particular analysis.
Because the retention factors for particular components of a mixture may vary if an analysis is
repeated under different conditions, a known sample is generally analyzed at the same time as an
unknown mixture on the same sheet of chromatography paper or slide. If the unknown mixture
produces spots having the same Rf values as spots from the known sample, then an identification
of the unknown components has been achieved. In this experiment you will be asked to
determine the retention factors for each color that makes up the dye of a particular candy and use
retention factor to determine which colors are the same.
Pre-Lab Questions:
1. Write the definitions for the following terms:
a. Chromatography
b. Retention factor
c. Mobile phase
d. Stationary phase
2. What chemical is used as the mobile phase in this experiment?
3. Red litmus paper will turn what color in ammonia?
Procedure
You’ll be working with a partner who will extract the dye from candy that is the same color as
yours, but a different brand. For instance, if you are doing blue M&Ms, your partner should be
doing blue Skittles. Each of you will extract the dye from the one brand of candy, but then
you’ll each run your own chromatogram on both blue dyes.
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Candy Chromatography Lab
Part A: Extracting the Dye from two brands of candy
1. Add about 150 ml of water to a 400-mL beaker.
2. Heat the water to boiling on a hot plate set to medium (adjust the heat to keep the water
just at the boiling point). Add more water if the level gets too low as the experiment
progresses.
3. Place six pieces of one candy (all of the same color and same brand) in a test tube, and
then add enough vinegar to cover them. Your partner should place six pieces of a
different candy (all of the same color and same brand) in a test tube, and then add enough
vinegar to cover them. Both candies should be the same color.
4. Heat the test tubes in your boiling water bath until the colored coating of the candy has
dissolved (avoid dissolving the interior of the candy).
5. Remove the test tubes and allow them to cool to room temperature. Your solution now
contains dyes, some sugar, and vinegar.
6. Pour the liquid from each test tube into another clean test tube, leaving behind all solids.
7. Add the 15-cm length of woolen yarn and 3 mL of vinegar to each test tube containing
the dye solution. Ensure that ALL the yarn is in the colored liquid, use a stirring rod to
push it down into the liquid.
8. Heat the tubes in the boiling water bath for about 5 minutes, stirring occasionally.
9. Remove the yarn using a stirring rod and rinse it with a little tap water (don’t rub it). The
dye should now be stuck to the yarn.
10. Place each yarn and about 5 mL of the 1.0 M ammonia solution in a clean test tube, and
mix with a stirring rod.
11. Test the solutions to make sure they are basic by placing a drop of it on a piece of red
litmus paper.
a. Using the glass end of a stirring rod, dip into the test tube and touch the litmus
paper with one drop of the solution.
b. If the paper stays red, add a few more drops of ammonia to the test tube and
retest.
c. Once the paper turns blue, continue to the next step.
12. Heat the test tubes containing the yarn and ammonia in the boiling water bath for about 5
minutes, stirring occasionally.
13. Remove the yarn and pour the solutions into individual evaporating dishes.
14. Heat the evaporating dishes gently on the hot plate set to low to concentrate the solution.
Stop just short of dryness—DO NOT let all the liquid evaporate.
Part B: Preparing the Chromatogram
1. Using the scrap piece of chromatography paper and a capillary tube, practice making
small spots of dye solution on the paper.
2. On the 14 x 10 chromatography paper, draw a straight baseline in pencil—do not write on
the paper with ink—approximately 2.0 cm up from the bottom of the sheet. (Consider
the 14 cm edges to be the top and bottom of the sheet.)
3. Place pencil dots on the baseline where each dye will be placed and label each of the dye
spot with color and candy (example – Blue M&M or red dye).
4. Using separate capillary tubes for each solution, place one spot of each of the following
solutions along your baseline:
a. Dye solution you prepared from candy.
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Candy Chromatography Lab
b. Dye solution of the same color, but from a different brand of candy, prepared by
your partner.
c. Separate spots of the standard solutions for the color you are working with (your
instructor will tell you which standard solutions to use)
In applying the spots, you should follow these guidelines:
a. Use a fresh capillary tube for each solution.
b. Place the first spot at least 3 cm in from the left edge of the paper and the last
spot at least 3 cm in from the right edge of the paper.
c. Leave about 2 cm of space between neighboring spots.
5. In pencil (not ink), label each spot along the bottom edge of the paper.
6. Holding the paper upright with the spots facing you, curve the two vertical edges away
from you and toward each other until they just touch each other (make sure they do not
overlap). Staple the touching sides together at the top and bottom of the cylinder you’ve
created.
Part C: Developing the Chromatogram
1. Add about 20 mL of the 1.0 M ammonia solution to the 600 mL beaker (not more than
1.0 cm deep). Then stand your paper cylinder alongside the beaker and check to see that
the level of the ammonia in the beaker is below the baseline on the cylinder. If the
ammonia level is above the baseline, pour out some of the solution and check again.
2. Once you are sure your spots won’t be submerged, place the cylinder in the beaker,
baseline at the bottom, as shown in Figure 1.
3. Cover the beaker with plastic wrap. Leave the setup undisturbed once the solvent has
begun moving up the paper.
4. When the solvent has traveled to just below the top of the paper cylinder, remove the
cylinder from the beaker and allow it to dry.
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Candy Chromatography Lab
Name ___________________________
Candy Chromatography Report Sheet
Lab Partner(s): ________________________________________________________
Lab Partner who has chromatograph attached: _____________________
Data:
Skittles Color
_______________
M&M Color
_______________
Skittles’ Colors
Solvent Height
Color Height
Rf=
M&M’s Colors
Solvent Height
Color Height
Rf=
Standard Solution
Colors =
Attach your chromatogram (or draw a diagram of it) here. (Or state lab partner that has
chromatograph)
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Questions
1. Were the same dyes present in the two different brands of candy? Where any of the
colors that make up the dyes the same? How did you determine they were the same?
2. Chromatography paper is fairly polar. How would you expect an ionic component to
behave when the mobile phase is a relatively nonpolar solvent, such as acetone? Would
such a component readily travel with the solvent or would it stay behind?
3. Which type of intermolecular forces would be responsible for the movement of an ionic
component?
4. How would you expect a relatively nonpolar component to behave when the mobile
phase is a nonpolar solvent? Explain your reasoning.
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