GT CHEMISTRY

Unit: Chemical Bonding

Name: ______Date: ______MOD: ______

Paper Chromatography of Powdered Beverage Mix

If you have ever watched a crime television program, you have probably noticed that law enforcement agencies often send their crime scene samples to a lab for analysis. This analysis typically involves separating various parts of the sample and identifying each chemical present. One method often used is chromatography.

Chromatography is a physical separation technique. The word “chromatography” comes from the Greek “chroma” meaning color and “graphein” meaning to write. There are several types of chromatography commonly used: paper, column, and gas.


In this experiment you will use paper chromatography to analyze different dye components of powdered beverage mix. Powdered beverage mixes typically contain a mixture of several dyes such as Yellow 5 (tartrazine) and Red 3 (erythrosine). Polar dyes should dissolve in the water and be carried up the chromatography paper. The more polar dyes will rise higher than the less polar or nonpolar dyes. You will analyze the rates at which each dye rises on chromatography paper using the retention factor, Rf.

OBJECTIVES

When you have completed this activity, you will be able to:

1.  Use liquid chromatography to separate dyes in powdered beverage mix.

2.  Calculate Rf values for each dye.

3.  Rank the polarity of each dye present.

MATERIALS

Concentrated solutions of various flavors of powdered beverage mix

Toothpick

Beakers

Deionized water

Chromatography or filter paper cut to approximately 5 cm × 8 cm

Ruler

Tape

PROCEDURE

1.  In pencil, draw a starting line 1 cm from the bottom of your chromatography paper. Label the paper below this line with the flavor of the beverage mix. Use the tooth pick to transfer a dot of concentrated solutions to the center of your line. Repeat with a second flavor. Record the drink flavor and list of dyes on the package in your data table.

2.  Pour deionized water into your beaker so that the level is less than 1 cm deep.

3.  Tape the strips of paper to your pencil and allow to hang into the water. The bottom of the paper should be in the water below the 1 cm line. Vary the amount of water if needed. Both strips should be at the same height.

4.  Record your observations below.

5.  Allow the strips to remain in the water until the water rises to within 1 cm of the top of the strip. Remove and allow the strips to dry.

6.  Draw lines indicating the level the water level and each dye rose. Measure each distance.

OBSERVATIONS

DATA

Figure 1:

Beverage flavor______Sample setup

Dyes listed on the package ______

Distance Traveled
Water
Dye Color ______
Dye Color ______
Dye Color ______
Dye Color ______

Beverage flavor______

Dyes listed on the package ______

Distance Traveled
Water
Dye Color ______
Dye Color ______
Dye Color ______
Dye Color ______


ANALYSIS

1.  The most common dyes in powdered beverages are yellow 5, red 3, blue 1, and red 40. List which are present in each of your samples. Are there any additional dyes?

2.  Calculate the retention factor (Rf) for each dye you observed using the formula:

Rf = (distance dye traveled) / (distance water traveled)

3.  Rank the dyes in order of polarity.

4.  How would your results differ if instead of using water as the solvent, you used a nonpolar substance such as carbon tetrachloride? What if you used a weakly polar substance such as acetone?

PRELAB: Paper Chromatography of Powdered Beverage Mix

1.  Define the following terms:

a.  Eluent-

b.  Mixture-

c.  Capillary Action-

d.  Mobile Medium-

e.  Stationary Medium-

2.  How does paper chromatography work?