Lab Report: Paper Chromatography printable pdf download

Lab: Paper Chromatography

Paper chromatography is a method of separating mixtures by using a piece of absorbent paper and a solvent. In

this process, the mixture to be separated is placed on a piece of dry filter paper. The paper is the stationary

phase. The solvent, or mobile phase, is allowed to travel across the paper by capillary action. As the solvent

front moves, the components of the mixture separate. Due to the difference in relative attraction which each

component in the mixture has to the paper and to the solvent, the parts of the mixture separate as each travels a

different distance up the paper. The components of the mixture which are most attracted to the solvent travel

farthest with the solvent. The components of the mixture which are most attracted to the paper move slower,

remaining closer to where they were originally placed, the origin. The different polarities of the paper, solvent

and mixture components determine the degree of attraction between each. (Remember, in terms of polarity, like

attracts like.) For example, if acetone is nonpolar and the paper is slightly polar, nonpolar components of the

mixture will travel with the solvent and be deposited farther from the origin, while the polar components will be

more attracted to the paper and be deposited closer to the origin.

In this experiment, you will place small spots of black ink, made by each of several different black pens, near

the center of a piece of filter paper. By means of a wick, solvent will be drawn to the center of the filter paper

and will then spread outward toward its edge. The different colored substances that make up the black ink

mixture will be distributed by the solvent along a path to the edge of the paper according to relative polarities.

You will use three different solvents of different polarities to obtain three chromatograms. Because each brand

of black ink is a unique mixture of colored molecules, each pattern on the paper, or chromatogram, is

characteristic of the brand of pen used. You will then make chromatograms of two unknown pen spots and

attempt to identify the pen which made each spot.

Chromatography is an important tool of the forensic chemist in solving crimes. This method can help to identify

drugs, inks, or other chemicals found at a crime scene. For example, chromatography could help scientists to

identify the brand of pen used to write a ransom note. It could also be used to determine whether an unknown

powder found on a suspect matches the drug used to poison a victim.

Procedure:

Radial Chromatography of Knowns

1. Obtain 3 pieces of round filter paper. Prepare each in an identical manner. (See sample set up on front

desk.) Use your pencil (not pen!!) to make a small hole in the center of the paper.

2. Use your pencil to draw a circle around this hole about the size of a quarter. (Pencil will not travel with

your solvent in the chromatogram because it will not dissolve in any of the solvents provided.)

3. Along this circle, make a dot with each of the black pens. Use a pencil to number the dots with the

corresponding pen numbers.

4. Fill each of three Petri dishes halfway with a different solvent. Use water in the 1

dish, ethanol in the

and acetone in the 3

. The acetone dish must be glass!!

5. For each filter paper, obtain a small piece of chromatography paper, roll it into a wick and place it in the

hole in the center of the paper. This wick will extend from the paper down into the solvent in the dish.

The solvent should then travel up the wick to the center of the paper and spread radially to the edges of

the paper.

6. Place the filter paper circle on top of the Petri dish with the wick extending into the solvent. The filter

paper itself should not be in direct contact with the solvent.

7. When the solvent has reached about 1 cm from the edge of the filter paper, remove the paper from the

dish and, using a pencil, mark the distance that the solvent front traveled. Allow the chromatogram to

dry.

Lab Report: Paper Chromatography

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