Ulrich and Fabian
CHROMATOGRAPHY
NAME___________________
Chromatography is a useful method for separating mixtures. The components or parts of
a mixture are not chemically combined. Therefore, they can be separated. Many
mixtures, such as food coloring and inks, consist of two or more dyes. These dyes
dissolve in water. Using chromatography, you can separate the different dyes because
they dissolve at different rates. You will see a pattern of colors. Each color will be a
single component of the mixture.
You may wonder how chromatography works. A small portion of the mixture
you wish to separate is put on an absorbent material such as filter paper or a paper towel.
A liquid called a solvent is absorbed into one end of the filter paper. This solvent soaks
the filter paper, dissolving the food coloring. If a dye in the food coloring dissolves
extremely well, it will move along the filter paper at the same rate as the solvent. If
another dye in the food coloring does not dissolve so well, it will not move so far.
The distance that a component dye travels on the filter paper is a property of dyes.
You can use this property to identify the dyes that make other colored mixtures.
STRATEGY
You will use chromatography to separate the components of a mixture. You will then
explain how chromatography separates a mixture.
MATERIALS
apron
5 test tubes
chromatography paper
5 food colorings
5 tooth picks
goggles
metric ruler
pencil
scissors
tape
PROCEDURE
1. Cut five paper strips (15 cm long and 2 cm wide) from.
Make diagonal cuts at one end of the strip so it comes to
a point. Use a pencil (do not use pen or ink) to mark a line
across the bottom width of the strip.
This line is called the “origin”. Draw another line across
the width of the strip 10 cm away from the first line. The
second line is called the “finish.”
2. Add water to each test tube so it is about 1-2 cm deep.
3. Place a small drop of food coloring on the center of the “origin”
line of a paper strip using a toothpick.
4. Carefully put the pointed tip of one strip in the water. Be careful
to keep the origin line well above the level of the water.
Water should begin to travel the length of the strip.
Ulrich and Fabian
5. Using four other food colorings, repeating steps 3 and 4. You will have five test
tubes, each with different food coloring. Be careful not to touch or disturb the test tube
while the water travels the length of the paper strip.
6. Allow each paper strip to soak up water until the coloring reaches the finish line.
Observe the paper strip for a few minutes and describe what is happening in the Data and
Observations section.
7. When the coloring reaches the finish line, remove the strip from the beaker and allow
it to dry in the air. The dyes can easily stain your hands and clothing, so do not
touch
the colored areas of the strip.
8. In Data Table 20-3, list the original shade of each food color mixture. List all of the
colors of the component dyes you observe on each strip.
9. List the shades of the five original food colorings on the black spaces on the back
page. Tape the dried paper strips to this page below the labels for each shade.
DATA AND OBSERVATIONS
Description of your experiment:
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________________________________________________________________________
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Data Table 20-3
Original food coloring
Component dyes________________
1______Green____________________________________________________________
2______Blue_____________________________________________________________
3______Yellow___________________________________________________________
4______Red_____________________________________________________________
5______Black____________________________________________________________
QUESTIONS AND CONCLUSIONS
1. What type of change -chemical or physical- took place in your chromatography
experiment?______________________________________________________________
How do you know?______________________________________________________
______________________________________________________________________
______________________________________________________________________
Ulrich and Fabian
2. The introduction stated that food colorings are mixtures. Based only on your
observations, do you agree or disagree with this statement? Give your reasons.
________________________________________________________________________
________________________________________________________________________
3. What information would tell you that a particular food coloring is made of a single
dye?____________________________________________________________________
________________________________________________________________________
________________________________________________________________________
4. Which component dye traveled the farthest distance for each food coloring?
a. food coloring
Green
dye__________________________
b. food coloring
Blue
dye__________________________
c. food coloring
Yellow
dye__________________________
d. food coloring
Red
dye__________________________
e. food coloring
Black
dye__________________________
5. Make a hypothesis about the relationship between dye color and distance travels on the
paper strip._______________________________________________________________
________________________________________________________________________
6. How would you prove or disapprove your hypothesis?__________________________
________________________________________________________________________
7. What do you think would be the results of your chromatography experiment if the
original food coloring were replaced with black ink? _____________________________
________________________________________________________________________
8. An art student made a drawing using felt-tipped markers. Unfortunately, the drawing
was splashed with water. The colors began to run and smear. Based on what you have
learned from this activity, explain what happened to the drawing.
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________________________________________________________________________
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Ulrich and Fabian
Food coloring
Food coloring