Community College of Philadelphia

Department of Chemistry

Laboratory Report Sheet
Name:

Date:

Email:

Laboratory Instructor:

Course Nbr.: CHEM 101 Distance

Section:

Experiment Nbr.: 4

Experiment Title: PAPER CHROMATOGRAPHY

Purpose:

Concepts related to the textbook:

Conclusion:

EXPERIMENT 4- PAPER CHROMATOGRAPHY

Background

Paper Chromatography is a purification technique used to separate a sample mixture into its pure components. The word “chromatography” is defined as “graphing of colors” (Tswett, 1906). Tswett used this technique to separate a mixture of colored pigments from leaves. Now, the technique is applied to colorless compounds and ions as well.

Chromatography separates substances in a sample mixture. The sample is placed on filter (or chromatography) paper that is set up so that the solvent can move over the surface (and the sample). The paper is called the “stationary phase” and the solvent is called the “mobile phase”. The end of the paper is dipped into the solvent, which then rises up the paper, by capillary action. As the solvent passes over the sample, which has been adsorbed on the paper, it begins to transport the sample upwards. However, each component in the sample mixture is dissolved by the solvent and simultaneously retained by attraction to the stationary paper phase to a different extent. This combination of effects causes each component in the sample to progress up the paper at a different rate thus causing the sample mixture to separate into its individual components.

Each component, in a given solvent system at a fixed temperature, can be characterized by a constant called a retention factor.

Rf. = Distance from origin to center of component spot

Distance from origin to solvent front

The origin is the point where the sample mixture was originally placed on the chromatography paper and solvent front is the line of most advanced penetration of the solvent system on the paper, i.e., where “wet” meets “dry.”

In this experiment, you will be separating black (or very dark) ink into its components.

Needed: 2 black felt-tip markers (different brands; non-permanent ink)

[Black ink is preferred but dark blue, red, purple or green will also work]

Salt

Water

3 sheets chromatography paper (Paper is available at the Chemistry Lab, W4-50, or you may use a coffee filter cut into a rectangle about 3″x 4”.)

8 or 16 oz. clear drinking glass

Saran wrap

Procedure:

1. Mix 1/2-teaspoon salt and 1/4 cup of water in the glass. Swirl until salt is dissolved

2. Take a piece of chromatography paper and draw a PENCIL line 2.0 cm from bottom. (This is the origin line)

3. Place 1 small dot of ink from each pen on the origin line.

4. Stand the paper in the glass. Be sure the origin line is above the surface of the solvent system. Cover the glass with saran wrap to prevent evaporation of the solvent and to saturate the atmosphere. PRECAUTION: Take care not to jiggle or disturb the even flow of the liquid solvent up through the paper.

5. When the solvent has risen to within (approximately) 2 cm of the top of the paper, remove the saran wrap and remove the paper from the glass. Wait ½-1 minute and then draw a pencil line along the solvent front (i.e. interface of wet and dry).

6. Lay the chromatogram on a clean surface and allow to dry completely.

7. Using the instructions above, make the appropriate measurements and calculations of Rf and complete the REPORT SHEET.

Sample Diagrams:

Solvent front (about 2 cm from top)

A3

B2

6.6 cm

A2

3.8cm

B1

A1

B Origin (2 cm from bottom)

At beginning At end

Sample Calculation:

For Component 2 in Ink A (A2)

Distance from origin to solvent front 6.6 cm

Distance of component A2 from origin 3.8 cm (measure to center of component)

Rf of component A2 = 3.8 cm/6.6cm = 0.58

Data

l. What is the distance from the origin to the solvent front (cm)? __________

2. a. What pen (brand and color) was used for Sample A? __________________

b. How many components were in Sample A? _____________

c. Fill in the table below for your Sample A.

It is unlikely that your sample has more than three components so be careful to distinguish between each component and ignore areas/colors that are obvious overlaps of components that have not fully separated from each other.

Component

Color of component

Distance of component from origin (cm)

Rf

1

2

3

4

5

3. a. What pen (brand and color) was used for Sample B? __________________

b How many components were in Sample B? _____________

c Fill in the table below for your Sample B.

It is unlikely that your sample has more than three components so be careful to distinguish between each component and ignore areas/colors that are obvious overlaps of components that have not fully separated from each other.

Component

Color of component

Distance of component from origin (cm)

Rf

1

2

3

4

5

4. Based on your results, what do you think of the effectiveness of paper chromatography as a purification technique? Could you improve upon the effectiveness?

5. Based on your observations of color and the corresponding Rf value, do you think that the two ink samples have any components in common? Why or why not?

6. Submit your chromatogram with your report (pdf or jpg is suggested).

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