The Mystery of the
Missing Mr. Brown!
Planning and Carrying Out Investigations
Team Name______________________________________
Team Members:
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
Define the Problem: Paper chromatography is a way to analyze mixtures,
such as ink, by separating them into the original chemicals that are included in their
makeup. Crime scene investigators use chromatography to identify and separate
many different substances. Detectives often use chromatography to identify drugs
from narcotics to aspirin in blood and urine. In this experiment, you will use
chromatography to solve a make-believe mystery about the identity of a kidnapper.
Chromatography Background: Chromatography is a way to look at
complex mixtures by separating them into their components. The separation of a
mixture into its components is a physical process, i.e. because the components of the
mixture are not chemically combined, they can be separated by physical means.
Here's how chromatography works: Different inks have different properties, such
as how much they can be dissolved in solvents. When you place chromatography
paper into the solvent, the solvent begins to move up the paper. As the solvent rises,
it dissolves the ink on the paper and separates the ink into its components. The
farther the ink travels, the more it is attracted to the solvent.
The Scenario: Mr. Brown has been kidnapped!! The kidnapper left a ransom note in
the school’s mailbox. FBI agents are on the way, but in the meantime there are tests
that can be performed to help solve the crime. Suspects have been narrowed down
to six teachers who all had a meeting with Mr. Brown after school yesterday. On
your table there are six black pens that were found on each suspect’s desk and now
all you have to do is determine which pen wrote the ransom note.
Procedure:
1. Label strips of chromatography paper at the top with the number of each
marker and the solvent to be tested. For example: #1 H2O; #1 Iso; #1 L
(H2O = water; Iso = alcohol; L= lemon juice)
2. Take the strips of chromatography paper and fold each piece about an inch
from the top.
3. Using the corresponding marker, draw a horizontal line near the other end of
the chromatography paper. Make the line about as high off the bottom as the
length of your thumb. Make sure to use the numbered marker that is labeled
at the top of the chromatography strip.
4. Use a pencil (you may need 2 pencils with 3 strips on each pencil) to suspend
the papers in each beaker. Make sure the strips do not touch the sides of the
beaker. Make sure the correct strips are in the correct solvent beaker
(Ex: all 6 H2O strips should be in the H2O labeled beaker)
5. Carefully add the correct solvent (H2O, Iso, or lemon juice) to the correct
beaker. Add just enough of each liquid so that it touches the bottom of the
hanging strip.
6. Describe what happens and set up a data table to record the results
(Google docs) (15 points)
7. Discuss with your group how do go about comparing the results of the tests
with the original ransom note.
8. Perform the tests on the ransom note
9. Compare the results on the tests on the ransom note with those of the
numbered markers.
Analysis Questions (Google docs)
1. What were the solvents in this experiment? (5 points)
2. Black ink is more attractive to which solvent? How do you know?
(10 points)
3. What colors are present in black ink? (5 points)
4. What do these colors represent? (10 points)
5. Which suspect is the kidnapper? Use data to support your claim
(15 points)
6. How might the ability to separating solutions into their components be
important to environmental engineers looking into water quality
issues? (25 points)
Taking Things Further
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Perform an experiment using water as a solvent on the three colored
markers – red, green, and brown
Make a data table showing your results (what colors did the marker
separate into?) (5 points)
Calculating the retention factor of the specific dyes in colored markers. To do so,
you need perform this additional step:
Using the ink samples after the ink has separated, each separated spot can be
assigned a retention factor (Rf ). This factor is characteristic of the specific dyes
in the colored markers. The Rf is a ratio of the distance the color spot travels

compared to the distance the solvent, or the water, travels. The Rf is calculated by
dividing the color distance by the water distance. This ratio should be a constant
for that specific dye on the chromatography strip and the solvent. It should be able
to be repeated in the same circumstances.
The following is an example of calculating the retention factor of a specific dye.
Actual tests on the inks used in the activity would have to be done to calculate the
answers to the retention factors of the inks.
Calculations for the following diagram:
Rf (magenta)
Water
level
-----------------
9.4 cm
6.8 cm/ 9.4 cm= 0.72
Magenta
6.8 cm
Rf (cyan)
3.5 cm /9.4 cm = 0.37
3.5
cm
Cyan
Ink
spot
----------------
Original
water level