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The Colors Of Kool-Aid

Description of Activity

Title: The Colors Of Kool-Aid

Overview: Working in small groups (2-4 students) students will perform a chromatographic separation and then design and conduct an experiment using chromatography. This laboratory exercise should take two or three fifty minute lab periods.

Materials: Skill Development Activity - Felt tip markers of several different brands, colors, and uses (permanent markers, Vis-A-Vis overhead pens, white board markers, etc.). Various solvents including water, alcohol, acetone, etc. Chromatography paper and/or filter paper. Evaporating dishes, petri dishes, graduated cylinders, or similar glassware.
Inquiry Lab Activity - Several different flavors of ÒKool-aidÓ (recommended at least six different colors). Chromatography supplies from the skill development lab.

Background

Chromatography (from the Greek chroma, for color, and graphein, to write) is a technique often used by chemists to separate the components of a mixture. Because of the simplicity and efficiency, this technique has wide applications for separating and identifying compounds such as drugs and natural products. Chromatography is what is generally done when people on T.V. say that they are sending something to the lab to have it analyzed.

The basis of chromatography is the partitioning (separation arising from differences in solubility) of compounds between a stationary phase and a moving phase. This brings about a separation as the components of the mixture travel with different speeds in the moving solvent.

Three methods of chromatography are: paper chromatography, column chromatography, and gas chromatography. In this experiment students will use paper chromatography to analyze different dye components of ink and Kool-Aid. The separation occurs as the mixture moves up the filter paper and each component is "left behind" at different points, depending on its relative solubility. In paper chromatography, a small spot of the mixture to be separated is placed at one end of a strip of paper, and the solvent is allowed to move up the paper, through the spot, by capillary action. The solvent and various components of the mixture each travel at different speeds along the paper.

The identity of components in a mixture can be deduced by comparing a chromatogram of the unknown with chromatogram of mixtures of components suspected to be present in the unknown. An additional aid in identification of a compound is its Rf value, which is defined as the ratio of the distance traveled by a compound to the distance traveled by the solvent.

Rf (substance) = dsubstance/dsolvent

The Rf value of a compound is a characteristic of the compound, the support, and the solvent used and serves to identify the constituents of a mixture.

Teaching and Learning Strategies

Prerequisite instruction:

A discussion of chromatography is necessary. Explain to students the process of chromatography and how to interpret the results.

At least two different setups for the chromatography are possible, the ascending strip technique using standard chromatography paper (or filter paper strips) and the horizontal circular technique using round filter paper.

The ascending strip technique requires a large beaker or graduated cylinder for the solvent. Place the solvent to a depth of 10-12 mm in the bottom of the cylinder. Obtain a piece of chromatography paper about 15 cm long. Spot ( a small drop of about 5 mm diameter) the strips with the solution being tested about 2 cm from the bottom of the strip. Allowing students to investigate the size of the spots and the height at which they should be placed would allow students to experiment and solve problems independent of specific instructions.

The horizontal circular technique uses Whatman #1 filter paper. With filter paper it is necessary to use a "wick" (a small piece of rolled filter paper) to pull the solvent onto the filter paper. The wick is inserted through a small hole in the center of the filter paper. The paper is spotted just off the center of the paper. The filter paper is placed over the top of an evaporating dish or petri dish with the wick resting in the solvent. A second petri dish can be inverted over the top to slow evaporation of some solvents. Four or five samples can be tested at one time using this setup.

A demonstration of common procedures used in paper chromatography is recommended.

Have the students do a guided chromatographic separation using different colored water soluble inks, being sure to include black and green colored inks (these will separate into different pigments.) Suggest that the student try as many combinations of ink and solvents as possible.

Before the students start the inquiry laboratory, they must realize that the Kool Aid must first be dissolved (for spotting purposes) and the spots must be heavy enough on the paper.

Safe Operating Procedures:

Wear safety goggles at all times while in the laboratory. Dispose of dry chromatography paper or filter paper in the dry trash. All solvents should be disposed of properly. Disposal method depends on the solvents used. Kool aid can be rinsed down the drain.

Skills Development Lab

Are all inks in felt tip markers identical?

Using the procedures demonstrated by your instructor test the ink used in felt tip markers. Try all combinations of markers and solvents that you have time to complete. Keep very careful records of your trials. Be creative.

Summary of Learning

The lab report should include a data table showing the combination of marker inks and solvents tested and a conclusion about the inks in markers is appropriate for this activity. Compare Rf values for each ink component. Are any of the components the same? Justify your conclusion.

Invitation to Learn

Now that you know how to do chromatography and how to interpret the results, how many food colorings or dyes are needed to make all these different flavors of Kool-Aid?

Assessment of Learning:

Suggested Evaluation Tools

In the formal lab report students should address the number (and perhaps kinds if known chromatograms are provided) of the food colorings used in Kool-Aid. They should show, by calculation of Rf values, how they reached the conclusions. Students should also include the chromatograms with their reports.

Alternative Evaluation Tools

Make a poster to exhibit your results. Include your chromatograms, samples or packages of the drink mixes tested, and an analysis and/or conclusion of your findings. The poster should include calculations comparing Rf values.

Multiple Choice Questions

Chromatography is useful for:

a. separating solutions into individual components.
b. separating compounds into individual elements.
c. separating subatomic particles in atoms.
d. separating materials prior to quantitative analysis.

In chromatography what causes the substances to separate?

a. Covalent bonding
b. Affinity for the solvent
c. Molecular weight of the substance
d. polarity of the solvent

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Updated September 26 1997 by Michelle Dumas