Paper Chromatography of Inks
The inks in marking pens are often mixtures of dyes of several basic
colors. In this MiniLab, you will use the technique of chromatography to
analyze the ink from several pens.
PROCEDURE
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Wear an apron and goggles.
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Obtain a clear plastic cup that is at least 6 cm high. From a coffee
filter, cut a strip of paper about 2.5 cm wide and about 2.5 cm longer
than the height of the cup.
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Place the paper strip in the cup so that the bottom of the strip just
rests on the bottom of the cup.
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Push a pencil through the top of the paper in such a way that when the
pencil rests on the top of the cup, the paper is suspended with its
lower edge just touching the bottom.
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Prepare several strips in the same way, one strip for each type of
marker ink you will analyze.
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Using one water-soluble ink marker for each strip, draw a narrow,
horizontal line across the strip about 2 cm up from the bottom. If
possible, include one black or brown marker.
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Add about 1 cm of water to the cup and suspend the first strip in the
water. The marker line must be above the water level when the strip is
suspended in the cup.
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Cover the top of the cup loosely with clear plastic wrap to reduce
evaporation. Observe and record the effect on the marker line as the
water moves up the paper.
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Remove the strip from the cup or beaker when the water level has risen
to just below the pencil. Lay the strip on a paper towel to dry.
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Repeat procedures 6 through 9 with each of your marker strips.
ANALYSIS
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Capillary action is the movement of a liquid upward through small
pores that exist in some materials. Did you note any evidence of
capillary action in this MiniLab?
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Does your evidence indicate that any of the marker inks were composed
of more than one pigment?
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Which colors contained the greatest number of pigments?