CANDY CHROMATOGRAPHY
BACKGROUND:
In Candy Chromatography, students will explore how the bio-chemical concepts of capillary
action, diffusion and affinity can be utilized to separate materials in solution. Capillary action, the
ability for liquids to flow against gravity, will cause candy dyes to be carried by water, and
ascend the coffee filter paper. Diffusion, the process by which fluids move from areas of high
concentration to areas of low concentration, will also propagate movement of dissolved dyes
through the filter paper. In the experiment, candy dyes are analogous to a mixture of similar
molecules that can be distinguished through their varying affinities for the filter paper.
Separation in chromatography occurs because each dye color has a unique affinity, or tendency
to interact with the molecules of the coffee filter paper. In effect, a dye’s affinity for the coffee
paper will determine how far a dye will travel up the paper. The higher a dye’s affinity for the
paper, the stronger its interaction will be with the paper and the shorter the distance it will
traverse. As a result, chromatography separates similar substances based on their affinity for
the chromatography medium.
Students will apply these key chromatography concepts ideas to explain important
biological processes in the human body, such as pulmonary gas exchange. If the dyes are
likened to gases in human lungs, then the chromatography paper represents pulmonary
membranes, across which the gasses diffuse. The gases, like the dyes, will travel different
distances across the pulmonary membrane based on their chemical properties. Moreover, the
gases will travel from areas of high concentration to low concentration. For example, highly
concentrated carbon dioxide in deoxygenated blood travels to areas of low carbon dioxide
concentration, such as the air in the lungs. Thus, chromatography enables humans to partially
rid their bodies of carbon dioxide and inhale oxygen. Ultimately, chromatography explains a
variety of other biological process, such as renal filtration, and has profound implications for the
future of bio-medical inquiry.
Upon completion of the experiment, students will connect the concepts of capillary action,
diffusion, and affinity to medical lab practices such as DNA gel electrophoresis. DNA gel
electrophoresis, for example, exploits the physical differences in strands of processed DNA as it
runs through a chromatography-like apparatus in order to isolate molecules of certain sizes,
shapes, and structures. The coffee paper in chromatography acts like the agar (sugar) medium
in gel electrophoresis that it can separate molecules based on intrinsic properties, size, in this
case. Thus, Candy Chromatography is not only an experiment demonstrating core concepts of
affinity, diffusion, and capillary action, but is also a tool for understanding lab applications and
discovering how our bodies work.
OBJECTIVES: By the end of the experiment, students should be able to do the following.
 Experimental: Use the scientific method to understand how chromatography utilizes
specific chemical affinities by comparing the lengths that dyes travel on filter paper.
 Biological: Recognize that Candy Chromatography is a simple experimental model for
diffusion in more complex biological systems such as gas exchange or renal filtration in
the human body.
 Technological: Use chromatography and the use of chemicals’ different affinities to
facilitate separation, to demonstrate the basis for many medical lab techniques
HYPOTHESIS:
Mixtures of dyes containing several elementary colors should split during chromatography
because each basic color has a different affinity for the coffee filter paper. Dyes comprised of a
single color should not split.
DURATION:
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Set-up time: 30 minutes (for material preparation and discussion)
Experiment's run time, data collection, and answering lab questions: 45 minutes
Take-down time: 5 minutes
MATERIALS:
For each 5-6 student team:
For each student:
Small packet of M&M or Skittles candies ($1) Cup (<10 cents each)
Coffee Filter Papers (Qty: 2; <5 cents each)
Straw
Scissor
Paperclip
Ruler
Water (100mL)
Pencil (do not substitute for a pen or marker)
Salt (1 tbsp)
Coffee stirrer
Small square of aluminum foil (< 10 cents each)
PROCEDURE:
1 EXPERIMENT SET-UP
1.1 Instruct students to answer questions in the pre-lab. Address any immediate questions
about wording or syntax. Then, discuss the material quizzed in the pre-lab material. The first
question: What direction do materials move in during diffusion? (answer: high concentration
 low concentration)
The second question: Exhaling carbon dioxide is caused by simple diffusion. What must be
the relative concentrations of inhaled air and deoxygenated blood in order for carbon dioxide
to be exhaled? (Answer: Immediately before the exhale, the carbon dioxide concentration in
deoxygenated blood is higher than the carbon dioxide concentration in the air in the lungs).
1.2 Teacher should perform the experiment using purple, green, and brown dyes using the
entire set of instructions outlined below. This will later be used for students to guess the
mystery elements.
1.3 Confirm that the secondary colors above split in the following ways: (Green: Blue, yellow;
Brown: Blue, Yellow, Red; Purple: Red, Blue)
1.4 Label each prepared strip such that only the teacher may identify the original dyes used for
each strip. Set all aside.
1.5 Introduce the experiment using concepts such as chromatography, capillary action,
diffusion, and affinity. Students should use the space provided under the “Concept Check”
section in the lab worksheet to note important ideas and provide examples. Key terms and
definitions for the educator are listed below:
Chromatography – the process by which dyes are separated according to individual
colors’ specific properties. These properties can range from size, affinity, and shape and
are widely used in biology and chemistry labs to purify materials. An example is the
current experiment. M&M dyes have different chemical properties, and thus different
affinities for the filter paper. The greater the affinity, the less distance the dye will cover.
The end result: different colors in the dyes travel different lengths. A health related
example is renal filtration. The tubular membrane (membrane covering the kidney
tubules which carry waste out of the body) is relatively permeable. Relative permeability
means that different substances are allowed to move across the membrane in different
amounts, depending on the chemical properties of the substance. Knowing the different
chemical affinities of molecules to the tubular membrane allows chemists to create drugs
that do not get filtered out easily (meaning have a high affinity for the membrane and do
not move through easily).
Capillary Action – the ability for fluid to flow against gravity through narrow spaces aided
by diffusion. The fluid’s interaction with the surface of the narrow space allows the fluid
to rise against gravity. Plants often use capillary action to deliver water to the leaves
from the roots for photosynthesis. Plant vessels, like all substances, contain narrow
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spaces at the molecular level. In Candy Chromatography, capillary action occurs when
water climbs the filter strip.
Diffusion – the process by which a substance moves from areas of high concentration to
areas of low concentration. In our experiment, water diffuses to the dry end of the strip
because there aren’t so many water molecules on the dry end of the strip. A
concentration gradient is established when two or more locations have differing
concentrations. A biological example of diffusion is through gas exchange occurring in
our lungs as carbon dioxide is removed from the body and oxygen is inhaled.
Affinity – The tendency for a molecule to be attracted to a nearby molecule, causing the
molecule to slow down in speed. Two molecules that attract prevent each other from
travelling far. In our experiment, molecules in the dyes with high affinity for molecules in
the chromatography paper will tend to attract each other and impede the dyes’ ability to
travel far. Affinity can be likened to magnetic pull. The stronger two magnets attract, the
less likely they are to move away from each other. Thus, the stronger two molecules
interact, or the higher their affinity for each other, the less the two molecules will
separate.
1.6 Divide students into groups of 5 or 6 depending on the number of candy colors available.
Ask students to pick one color in the candy assortment and write their respective colors in
blank provided after “My color is ____” in the lab worksheet.
1.7 Set the stage for investigating color by asking what they think makes up the dye surrounding
the candy. Instruct students to answer the next question – this question is meant to connect
the background of chromatography to the procedure of the experiment. The question states:
The dyes have many similar properties, but can be differentiate by their color and certain
chemical properties. Please circle the correct underlined phrase. (Answer: The different
dyes have different chemical properties, and so they will interact in different ways with the
coffee filter paper.)
1.8 Have students write their own hypotheses predicting whether their colors will separate using
chromatography under the “Hypothesis” section of the lab worksheet. Encourage including
the scientific concepts that justify the given hypothesis.
2 EXPERIMENT EXECUTION
2.1 Each student should cut the coffee filter into a 1 inch wide strip. The length of the coffee
filter should exceed the height of the cup by a couple centimeters.
2.2 Students should pencil in a small dot 2 centimeters from one end of the strip and label the
candy color on the other end of the strip. Note: The dot will serve as a marker for applying the
candy dye later in the experiment.
2.3 To prepare the dye solution, take the aluminum foil and apply a small drop of water using
the straw as a pipette. Dip the straw beneath the water, the place thumb over the top of the
straw, raise the straw out of the water, and release thumb over the aluminum foil. The water will
release from the straw onto the aluminum foil. Place candy in water and wait about a minute for
the dye to dissolve. If students ask, explain that the straw was used in order to measure a
specific amount of water.
2.4 Now we will spot the colors onto the filter paper. Take a stirrer and gently dampen the tip.
Lightly touch the stirrer to the colored dye and place on the filter at penciled dot.
2.5 Let the filter strip to dry for 2 minutes.
2.6 Repeat steps 2.4 and 2.5 twice for a total of three applications.
2.7 To prepare the solvent, take a cup and pour just enough water to cover the bottom of the
cup. Note: The water level should be as shallow as possible so that when the student puts the
filter paper in, the dye dot will initially be above the water level.
2.8 Add a pinch of salt (the amount that can fit between your thumb and forefinger) to the water
in the cup. Swirl the cup vigorously to dissolve salt in water.
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2.9 Carefully, lower the filter paper into the cup. Be sure to keep the dye on the filter paper from
touching the solution. Use the paperclip to suspend the filter paper from the edge of the cup.
2.10 Have students observe the filter paper for 2-4 minutes and record their observations in the
lab worksheet under the “Observations” section. Urge students to incorporate the concepts of
capillary action, diffusion, and chromatography in their observations.
2.11 When the salt solution is about a centimeter from the top, students should unclip the filter
paper from the cup and place filter paper on a dry surface.
3 EXPERIMENT TAKE-DOWN
3.1 Students should dispose of their stirrers, cups, aluminum foil, and used candies. Students
may recycle wooden stirrers, cups, and aluminum foil if a recycle bin is available. Note:
Students should refrain from eating used, unsanitary candies as tempting as that might be.
3.2 Students should keep the coffee filter strips to compare individual results in groups.
DATA ANALYSIS AND QUESTIONS TO CONSIDER:
Review Hypotheses: Ask students if their chromatography experiment supported their
hypothesis. If it did not, have them justify why under the “My Hypothesis” section.
Sketch the Strip: After the strips have dried, students should sketch their filter strip in the
dotted rectangle labeled “My Filter Strip”. Students should be sure to include the penciled dot
where the dye was applied and where the dye diffused over the strip.
Comparing Results: Students should compare their results with their teammates and report
their comparisons under the “Observations” section of the lab worksheet. Students should now
be given the prepared strips and asked to predict the original colors of each of the secondary
color strips based on the results of chromatography. Students are expected to justify their
results by citing common chromatography results among their observed results and among the
observed colors in the teacher’s strips.
Lab Questions: Have students answer Question 2 through the Challenge Question in teams. If
there is time remaining, instruct students to discuss and answer the Super Challenge, and
Beyond the Super Challenge questions. The answers to the questions are provided below.
Answer to Question 1: Most candy dyes are not made of one color. Often they are a
combination of two or three dyes that are used to generate the color that we see. For example,
if a green M&M was used in the experiment, chromatography should separate the green dye
into its primary colors of yellow and blue. Candy companies often mix the two dyes to generate
the green color. Similarly, the air we breathe is not made up of only one gas – it is a composite
of gases. The air we breathe undergoes chromatography in the lungs, when certain gases such
as oxygen and carbon dioxides move past the pulmonary membrane, and other gases such as
argon and nitrogen do not.
Answer to Question 2: A dye’s specific affinity for the coffee filter determines the distance it is
carried. If a blue dye, for example, travels further than a red dye, the red dye must necessarily
have a higher affinity for the filter paper than the blue dye.
Answer to Question 3: A possible example of diffusion in our body could be renal diffusion.
After use by the muscles, the blood carries many impurities and waste, such as urea. The fluid
in the kidneys is constantly emptied, and therefore has a lower concentration of the impurities
and waste. When the blood is passed over a renal membrane, much of the waste diffuses out of
the blood (high concentration of waste) to the fluid (low concentration of waste, as it’s emptied
often). Thus, the principle of diffusion allows renal filtration, keeping substances from building up
to toxic levels in our blood. Note that the movement of any physical substances that does not
depend on concentration or permeable barriers is incorrect, i.e. muscle movement.
Answer to Challenge Question: Like chromatography, gel electrophoresis utilizes chemical
properties to separate distinct molecules, but unlike Candy Chromatography, gel
electrophoresis operates on size, not affinity. Strands of DNA of different lengths and are then
run through a sugar medium. The smaller DNA fragments move farther than the larger
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fragments as the smaller fragments do not become tangled in the medium and therefore are not
slowed down.
CONCLUSIONS:
Students should write their own conclusions about their specific dyes in the “Conclusion:
section of the worksheet. Before officially concluding the investigation students should discuss
what they learned about the technique of chromatography as a group.
Example: “Chromatography allows us to separate dyes into component colors based on the
dyes’ specific affinity for the coffee filter paper. The green dye from a green M&M separated into
two colors yellow and blue because the yellow and blue dyes have different affinities for the filter
paper. Furthermore, the blue dye moved further than the yellow dye because the blue dye has
less affinity for the paper than yellow dye.”
Scientist Name: __________________________
Candy Chromatography Lab Worksheet
Pre-Lab
1. What direction do fluids move in during diffusion? Please draw an arrow in the right direction:
High Concentration
Low Concentration
2. Exhaling carbon dioxide is caused by simple diffusion. What must be the relative
concentrations of inhaled air and deoxygenated blood in order for carbon dioxide to be exhaled?
Please circle the correct adjective:
Immediately before the exhale, the carbon dioxide concentration in deoxygenated blood is
higher/lower than the carbon dioxide concentration in the air in the lungs.
Concept Check: Please fill in the definitions for each of the stated concepts
Chromatography –
Capillary Action –
Diffusion –
Affinity –
Lab-Write Up
My Color Is: ________________________
The dyes have many similar properties, but can be differentiate by their color and certain
chemical properties. Please circle the correct underlined phrase.
The different dyes have different chemical properties, and so they will interact in different
ways/in the same way with the coffee filter paper.
My Hypothesis: What will happen in this experiment? How will the different dyes interact
with the coffee filter paper?
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Observations:
Directions: Write what you see and at the end sketch what your filter strip looks like.
Lab Questions
My Filter Strip
Question 1: The dye can be likened to the air we breathe in. Is your color made up of other
colors? How can you tell? What does this imply about the gasses in the air we breathe?
Question 2: Why do some dyes move further than others?
Question 3: In our experiment, water diffuses from the wet end of the filter strip to the dry end
of the strip – that is, it moves down its concentration gradient from areas of high concentration
to areas of low concentration. The diffusion of water is called osmosis. Besides gas in your
lungs, what is an example of diffusion in our body? (Please explain/discuss your answer with a
classmate.)
Question 4: Look at the three strips the teacher prepared. If you know that only green, purple,
and brown were used in these three strips, how can you use your results to find out the original
color of each of the strips? How do you think scientists use chromatography like you did to find
out the identity of molecules and proteins of a certain size and property?
Challenge Question: Gel electrophoresis (apparatus shown
on the right) separates DNA based on size. When a gel is
run, some DNA strands move further than others. (Explain
the medium) How is electrophoresis similar to
chromatography?
Conclusions:
Guiding Questions:
What is the implication of dyes moving different length?
Did your observations support your hypothesis?
What did you learn from this experiment?
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