Names of lab group
Date
Chromatography Lab
Chromatography is a laboratory technique that is used to separate the components of a mixture. It
allows you to see the different components, and also lets you calculate how far each component
has travelled, letting you accurately identify and compare each component. Chromatography
works because in a mixture you have bigger molecules and smaller molecules. As the water
moves up a piece of chromatography paper with the mixtures of dye molecules on it, the bigger
molecules move slower than the smaller ones, and therefore get left behind.
In this lab, you will examine the ink used to write a “ransom note” and compare them to samples
of ink used by several suspects.
Purpose: To identify which pen was used to write the “ransom note.”
Materials:
-two 250 mL beakers
-4 unknown sample pens
-pencil
-4 strips of chromatography paper
-“ransom note” chromatography strip
-ruler
Procedure:
1) Take one of the unknown sample pens and place a dot on the pencil line at the bottom, in the centre of
the strip. Then, use a pencil to write the brand of pen on the top of the strip.
2) Repeat step 1 for the other 3 pens.
3) Tape the top of a paper strip to a pencil, and let it hang across the top of the beaker. (See diagram on
board). If you have more than one strip in a beaker at a time, the strips should NOT TOUCH.
4) Add just enough water so that the TIP is IN the water, but the DOT is ABOVE the water.
5) Wait.
6) Remove the strip when the water has almost reached the top of the paper. Do this with all 5 strips of
paper, including the “document in question.”
7) On EACH strip, use a pencil to mark the final place that the WATER reached. Measure the distance
between the starting line and the final line of the water. Record this in the table below in the 4th column.
8) On EACH strip, measure the maximum distance that EACH colour travelled from the starting line.
Record this in column 3.
9) Complete the table by calculating the “Rf Value”. Divide column 3 by column 4 for EACH colour.
Results (10 marks)
Brand of
Pen
Document
in
question
Colours seen in
each pen (may be
less than 4 colours,
may be more)
Distance that
EACH colour
moved (d1)
Distance that the
water moved (d2)
Rf Value (calculate
by d1  d 2 )
Questions
Look at the calculated Rf values for each colour. The document in question should have very
similar Rf values for EACH of its colours compared to the test pen. In your opinion, based on
these values, which pen was used? Explain in complete sentences. (2 marks)
Are you confident in your answer enough so that you’d testify in court about the identity of the
pen used to write the ransom note, knowing that your testimony may send someone to prison for a
long time? Why or why not? (2 marks)
For the document in question, which colour has the largest molecules? Which colour has the
smallest molecules? How do you know? Refer to introduction for a hint. (2 marks)
Tape your dry chromatography strips to the paper below.