The Case of the Kidnapped Snowman
A CSI Chromatography Lab
Oh No! There’s been a tragedy in the kingdom of Arendelle. Anna’s good friend Olaf has
been kidnapped! Fortunately, the kidnappers left behind a ransom note and Anna knows how she can
figure out who wrote the note. All she needs to do is apply some of the knowledge she has gained in
science class and she’ll know how to quickly find Olaf!
Background: Chromatography (from the Greed word chromos for color) is the collective term for a
family of laboratory techniques used in the separation of mixtures. This procedure is the physical
separation of a mixture into its individual components.
We can use chromatography to separate the components of inks and dyes. The process can also be
used to separate the colored pigments in plants or used to determine the chemical composition of
many substances.
To prove that an ink sample is a certain brand, it is necessary to calculate the Rf (retention factor)
values of the different colored chemicals present in the marker. Rf is a calculation that compares the
distance the solvent traveled up the paper strip to the distance a pigment traveled up the same strip.
The Rf value is calculated using the following simple formula:
Rf value = ____Distance traveled by solute (pigments in the ink)_____
Distance traveled by solvent (water)
Objective: Anna has contacted you to help with investigating the kidnapping of Olaf. She has brought
you the ransom note and a list of 4 possible suspects – Oaken, Hans, Kristoff, and the Duke of
Weselton. When you questioned each of the suspects you found that each person was carrying a
black writing utensil. Your job is to utilize the process of chromatography to determine which
pen/suspect wrote the ransom note.
Materials:
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1 250mL beaker
Chromatography paper (or filter paper)
Samples of black markers
Water
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Pencil
Small binder clip
Metric ruler
Calculator
Procedure:
1. Using one strip of filter paper, measure and draw a light pencil line 2 cm from the bottom of the
strip.
2. Pour about 10 mL of water into the large beaker.
3. Send one group member to the evidence table with a piece of filter paper to choose a marker
to test. Record the letter of the marker at the top of your filter paper. Use the marker to make a
solid dot of color in the center of the pencil line you already marked. (Leave the marker at the
evidence table!)
4. Carefully lower the filter paper into the water BUT make sure the color dot stays above the
water level. If the dot falls below the water level, you will have to start over.
5. Once the paper is at the right level, use the binder clip to attach the end of the paper to the
pencil so the pencil rests on the edge of the beaker.
6. As soon as you put the paper in the water, begin timing for 5 minutes.
7. After 5 minutes, remove the paper from the water and let dry for a few minutes.
8. Repeat this procedure for 3 more markers.
9. After you have tested the 4 markers, check with your teacher to get an ink sample from the
ransom note and repeat the procedure with the sample.
10. Measure the distance the ink traveled (measure from the pencil line to where the ink stopped)
and the distance the water traveled (measure from the bottom of the paper to where the paper
is no longer wet). Record this information in the data section. Then, divide the distance the
ink traveled by the distance the water traveled to get the Rf value and record that information.
Data:
In your science notebook, copy the following table for each of the markers that you test. Tape your
chromatograph in your notebook next to the table that matches it.
Pen/Marker:
Color #1
Color #2
Color #3
Color #4
Brand:
Name:
Name:
Name:
Name:
# of Colors:
Solvent Distance (mm):
Distance (mm):
Rf Value:
Distance (mm):
Rf Value:
Distance (mm):
Rf Value:
Distance (mm):
Rf Value:
Discussion and Conclusion (answer in complete sentences):
1. What component of this experiment is the solute? Which one is the solvent?
2. Is chromatography a physical or chemical means of separation? Why?
3. Why do you think it was important to make sure the dot of ink did not fall below the water level
in the beaker?
4. Were there any markers that did not separate in the water? If so, which ones? Why do you
think they “refused” to separate?
5. Do you think linking a brand of pen or marker to the crime is enough evidence to convict a
suspect? Why or why not?
Extension:
If your group finishes early, try using rubbing alcohol to test the markers that did not separate. Follow
the same procedure as above and create a similar table for the results. Did the ink separate using the
rubbing alcohol? If so, why do you think it worked in alcohol, but not water? Which of the solvents –
water or rubbing alcohol – worked best? Why?