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Which Food Coloring Dye Has the Highest RF Value?
(Handwritten)
Many commercially available food dyes are mixtures. Paper chromatography is used in this experiment to
separate the dyes and determine their Rf values. Chromatography involves a mobile phase and a stationary
phase. In paper chromatography, the stationary phase is the paper that contains and supports the mobile
phase. The mixture to be separated is placed at one end of the paper. As capillary action draws it up the
paper, the mobile phase (solvent) passes over and dissolves the mixture. The components of the mixture
differ in their attractions to the mobile and the stationary phases, causing each to migrate at a different rate
up the paper. Thus, the components of the mixture separate as they migrate up the paper.
The ratio of the distance traveled by each component to the distance traveled by the solvent front is described
as the Rf value or
MATERIALS
jumbo pipet (1)
scissors distilled water
thin-stem pipet (1)
metric ruler (1)
pencil (1)
chromatography paper
mixtures: water soluble pens, food dyes, or acid-base indicators
1. Cut a strip of chromatography paper (square filter paper found in the filter paper
box) so that is about 0.5 cm wide by 15 cm long.
2. With a pencil, make an “X” 2 cm from one end of the paper strip.
3. Make a small dot of the mixture to be tested on the “X” and let it air dry. Be sure to
keep the dot small (2-3 mm wide). See diagram at right.
4. Cut off the tapered portion at the tip of a jumbo pipet.
5. Insert the stem of a thin-stem pipet containing solvent all the way to the bottom of
the jumbo pipet and squeeze out 5 drops of solvent. Remove the pipet carefully so
that the sides of the jumbo pipet do not get wet (see Figure 1).
6. Insert the prepared chromatography strip into the jumbo pipet; the end with the
mixture spot should go in the pipet. The end of the paper strip should touch the
solvent but the spot should be above the solvent. Insert a stopper into the open
end of the pipet to support the paper (see Figure 2).
7. Allow the solvent to travel up the strip. When the solvent almost reaches the end
of the strip, take the strip out of the pipet. Mark the leading edge of the solvent
and the approximate center of each colored region.
8. Measure the distance the solvent traveled from the “X” to the leading edge.
9. Measure the distance each component of the mixture covered from the “X” to the
approximate center of each colored region.
10. Calculate the Rf for each component in the mixture.
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ANALYSIS
1. Distance traveled by the solvent: __________
2. List the color of each component and the, distance traveled.
Color of Component
Distance Traveled by Component
3. Calculate the Rf value for each component. Show your work.
4. Why should one not use an ink pen or other similar marker to mark the starting point?
5. If a particular component had a greater attraction for the paper than it did for the solvent, would you
expect the component to be near the origin or the top of the paper after allowing the chromatogram to
form?
6. If one component has an Rf value of 0.64 and another component has an Rf of 0.87, how far apart would
the two components be from each other after the solvent has traveled 12.0 cm? Show your work.
7. Write a conclusion paragraph about what you learned.