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WHAT WILL YOU DO?:
Are you glued to the television
as your favorite detective finds a mysterious substance at
the scene of the crime? As the evidence is collected, someone says, "We'll
send this to the lab for identification." How does the laboratory
figure out what that substance is?
Chromatography is a technique used to separate mixtures.
Chromatography is used by crime
laboratories to identify clues such as blood,
ink, or other substances found at a crime
scene. Chromatograms of these clues are
compared against chromatograms of known
substances for identification.
In this experiment you get to be the detective! Can you identify
the 12 color markers?
STEPS TO FOLLOW:
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Good researchers always think about their experiment before they start. They
try to evaluate the test procedures and figure out what's
going to happen. Look at the chart
of completed chromatograms and guess what color marker was used for
each of the samples from A to R. Match the
number of the marker to the letter of the
chromatogram. Use one of your data
sheets to record your guesses.
Check the answer sheet. Are you surprised?
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MATERIALS:
12 Different Water-Soluble Color Marking Pens
Transparent Tape
Tap Water
Pencil
Paper Towels
Transparent Plastic Cup
3 Coffee Filters Cut Into 12 1" X 5" Strips
2 Copies Of The Data Collection Sheet
(Note: This demonstration can be a class or team activity.
If using student teams duplicate these supplies for each team.)
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Using a clear plastic cup, fill cup with about 1" of water.
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Take a strip of filter paper and draw a line about
1" from the bottom. If the marker is weak
you may redraw the line darker to get more ink on the paper.
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Take a pencil and tape the top of the
strip to the pencil so that the strip will touch the
water, but the line of ink at the bottom of
the strip does not touch the water.
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Set the pencil on top of the cup so the strip
hangs down. Don't let the ink touch the water!
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Remove the strip from the cup when the water has traveled about 3/4 of
the way up.
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Lay your test sample on a paper towel to dry. Repeat the test for
all 12 color markers.
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Looking at your chromatograph chart, write on your second data sheet
the number of the marker that REALLY belongs to each letter.
Compare your experimental
results with your guesses. Were you right? What colors
looked different after being tested in water?
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