In the chromatography process, two phases are required for the separation of the components (or compounds) in the mixture, the mobile phase and the stationary phase. The mobile phase consists of the components of the mixture and the solvent-the solvent being called the elute or eluting solution (generally a mixture of solvents of differing polarities). The stationary phase is an adsorbent that has an intermolecular affinity not only for the solvent, but also for the individual components of the mixture.

As the mobile phase passes over the stationary phase, the chromatograph develops. The different components of the mobile phase have different affinities for the stationary phase. The components with stronger affinity for the stationary phase move shorter distances while those with lesser affinity move longer distances along the stationary phase during the time the chromatograph is being developed. Separation, and subsequent identification, of the components is thus achieved. The leading edge of the of the mobile phase on the chromatograph is called the solvent front. When the solvent front reaches the edge of the chromatography paper, the developing of the chromatograph stops.

For a given eluting solution, stationary phase, temperature, and so on, each component of a mixture is characterized by its own Rf (ratio of fronts) factor:

Rf = distance from origin to final position of component color = Dion

distance from origin to eluent front Dsolvent(water)

Objective-to determine the component colors of various samples of ink

Materials

scissorstapemetric ruler600 mL beaker

stirring rodfilter papercolored pen(s)

Prelaboratory Assignment

1. Define the mobile phase in chromatography. What is the chemical component of the mobile phase in this

experiment?

2. Define the stationary phase in chromatography. What is the stationary phase in this experiment?

3. Define Rf value for a component. How will it be measured in this experiment?

4. A representation of an eluted and developed paper chromatograph of a mixture of dyes is shown at right. Use a ruler

to determine the Rf value for each dye in the mixture.

In Class Procedure

NOTE: Touch the filter paper “chromatograph” the least amount possible to ensure the best results.

1. Obtain a piece of filter paper that has already been prepared for you, or create your own by folding and cutting as

described by your teacher.

2. On one of the longest edge of the filter paper, draw a pencil line 2 mm “up” completely across the longest edge of the

paper. This is now the “bottom” of the chromatograph.

3. Using a pen containing ink to be tested, make one dot of ink such that the top of the dot meets the underside of the

pencil line. Repeat this for each different sample of ink to be tested, making sure the ink is equally distributed across

the pencil line and a label of the different sample(s) of ink to be tested is present for each.

4. Place enough water in the bottom of the beaker to just cover the bottom of the beaker.

5. Curl the filter paper into a cylinder shape making sure the dots are on the outside, and tape the ends such that the

shape is permanent but the filter paper sides do not touch.

6. Insert the chromatograph into the beaker. Make sure the pencil line end is closest to the water and that the filter

paper does not touch the sides of the beaker.

7. Allow the solvent front to climb up the chromatograph until it is within approximately 2 mm of the top of the filter

paper.

8. When the solvent front has reached the appropriate height, remove the paper from the beaker, and draw a pencil

line marking the solvent front. Do this carefully so as not to rip the paper, and quickly so as not to lose the solvent to

evaporation. (It may also be necessary to circle the different components of the mixture while the solvent front is

still present to ensure good measurements later.)

9. Allow the chromatograph to dry

Data Table

Record the measurements obtained from your experiment here.

Sample / Component(s) / Dsolvent value (mm) / Dion value (mm) / Rf

Calculations

Show the equation used and work for the calculations on one of the Rf values from the table above.

Post-Experiment Data Analysis

1. Which samples appeared to be composed of the most different colors?

2. Do any of the colors in the different samples appear to have the same Rf value? If so, which ones?

3. What information can you learn about samples containing colors with the same Rf values?

4. Which color that separated out of each type of the samples appears to be the least soluble in water? Which is

the most soluble in water?

Least:Most:

5. If the solvent contained a chemical that was said to be volatile, why would it be necessary to cover the beaker with

plastic wrap or some kind of cover?

6. Suppose two ink components have the same Rf value. Would it be correct to say that the two inks are identical?

Explain your answer.

Conclusion

Write a conclusion for this experiment. A well written conclusion should:

  • Restate the purpose of the experiment
  • State the results of the experiment and/or list any results from evaluation methods used
  • Compare the results with the objective/purpose of the experiment and any standard values you might have to compare your work against by stating whether the results were too high or too low.
  • Hypothesize why the errors occurred and what might be changed to avoid these errors
  • Use past tense, passive voice, and avoid using any pronouns in this conclusion