Candy Chromatography
Introduction:
Paper chromatography is an introductory concept that opens into many different kinds of chromatography,
such as gas, column, thin-layer, and other types of chromatography that are familiar to all chemists. The
idea of the mobile phase is the most important step in chromatography because this is the step where the
separation occurs. In this lab, the separation of the dyes used in two different kinds of candy is performed.
By comparing the Rf values of the dyes in each of the candies, we can hypothesize that the dyes with the
same Rf values are the same dye. However, since the separation of the dyes is dependent on many different
factors, we can only guess that the two dyes are the same compound unless the name of the dye is given on
each package and is the same on each.
Purpose:
To separate and compare the dyes found in different kinds of candy.
Materials/Equipment:
2 400 mL beakers
2 Chromatography strips
Ruler
Pencil
2 pieces of plastic wrap
50-mL graduated cylinder
Vinegar
Water
M & Ms and Skittles
Tape
Safety Considerations:
• Always wear goggles in the lab.
• Do not eat any of the candy because it may be contaminated.
Procedure:
1.
To one of the 400 mL beakers add 10 mL of water and cover with plastic wrap. To the other
beaker add 10 mL of vinegar and cover with plastic wrap. These will be your chromatography
chambers.
2.
On each piece of chromatography paper, draw a PENCIL line 1.5 cm from the bottom of the
paper. On the line you drew, make one mark in the middle of the line. Make one mark on each
side of the first (it should be half the distance from the middle mark and the edge of the paper).
Both papers should now look like this:
NOTE: You are preparing two identical chromatograms, so do the following step for both pieces of
chromatography paper.
ASIM Candy Chromatography
Revised: 2/06
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3.
Obtain a dark M&M, a light M&M, and a dark Skittles. Dampen the dark M&M and make a
smudge on one of the three marks on the line. Repeat with the light M&M on the second mark and
the Skittle on the last mark.
4.
Wait about two minutes to make sure the smudge is completely dry. Then place one paper in the
water beaker and the other in the vinegar beaker at the same time. (The smudged end of the paper
goes in the bottom of the beaker. Make sure that the line you drew is above the liquid level in the
beaker!) It may help to fold the paper where it leaves the beaker to keep it from sinking down into
the beaker.
5.
Replace the plastic wrap and allow the chromatogram to develop until the solvent (the vinegar or
the water) nearly reaches the top of the beaker. At that point, remove the paper from the beaker
and draw a PENCIL line across the paper to mark how far the solvent moved up the paper.
6.
Clean your area by dumping and rinsing the beakers.
ASIM Candy Chromatography
Revised: 6/06
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Data:
In the space below, tape both of your chromatograms.
Now calculate the Rf factor for each color on each chromatogram. Use the following formula:
Rf = distance color moved from original spot on line
distance solvent moved from line
Chromatogram in water:
Chromatogram in vinegar:
ASIM Candy Chromatography
Revised: 2/06
Color -
Rf -
Color -
Rf -
Color -
Rf -
Color -
Rf -
Color -
Rf -
Color -
Rf -
Color -
Rf -
Color -
Rf -
Color -
Rf -
Color -
Rf -
Color -
Rf -
Color -
Rf -
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Questions:
1.
Did your dark M&M and Skittle have any of the same dyes? Why or why not?
2.
Compare the M&M you spotted on the water chromatogram to the one on the vinegar
chromatogram. Did they develop differently? If so, what do you think could have caused this
difference?
3.
Do you think that the mobile phase (solvent) affects the Rf? Why or why not?
4.
How could you tell if yellow M&M's and yellow Skittles use the same dye?
5.
Explain in your own words why the colors in the candy separated when you allowed the water or
the vinegar to climb the paper.
6.
Define "chromatography" in your own words.
ASIM Candy Chromatography
Revised: 6/06
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