When working in a lab, scientists often need to identify different molecules that are present in a sample they are studying. There are many ways to identify unknown molecules/chemicals in a sample. The method you will be using today is called Paper Chromatography and consists of 2 steps. First, you will separate the unknown chemicals and then you will identify them. This process can also be applied to the food we eat everyday.
When you eat food or drink liquids you are trying to get important chemicals to your cells. (chemicals that your cells might use for energy or maybe to build more cells. ) Look at the food label below, though, and you’ll see a list of several chemicals that your cells cannot use. These chemicals may be added to keep the food from spoiling, give the food a flavor or texture that makes it taste better, or add color to the food/drink to make it look more appetizing so you will buy it. Many of the foods and drinks you buy each day would be clear or white without the addition of food dyes (artificial colorings).
Knowing this, we can ask what food dyes are used to make Kool-Aid, for example, look appetizing? Without food dyes, ALL flavors would be clear. In order to identify the food dyes in Kool-Aid, you must first separate them, and you will do this using paper chromatography. II. Materials: • 2 chromatography tubes • 2 strips of chromatography paper • Lemon-lime Kool-Aid solution • 1 pencil • 2 toothpicks • Grape Kool-Aid solution • Solvent (alcohol, salt, & water) • ruler III. Procedure: DAY I: Separation of Chemicals 1. Obtain all the supplies you need (at supply table). 2.
Cut 2 strips of chromatography paper so that each is about an inch longer than the tubes. 3. Cut one end of each paper strip to form a point (see drawing 1). 4. Draw a straight line across each strip an inch above the bottom of the tip. 5. Label the top of one strip “GRAPE” & the other “LEMON-LIME. ” 6. Use a toothpick to place a dot of grape Kool-Aid on the center of the line you drew (see drawing 1). Do the same with the lemon-lime Kool-Aid. 7. Poke a toothpick through the opposite end of the strip (see drawing 2). 8. Add a small amount (about 1/2 inch) of solvent to the 2 tubes. 9.
Lower each strip into a tube so that the tip of the paper touches the top of the solvent. DO NOT LET THE DOT OF KOOL-AID TOUCH THE SOLVENT DIRECTLY. (see drawing 2). The solvent will begin to move up the strip, dissolve the food dyes, and carry them upwards. 10. Leave the strips in the tubes for 30 minutes. 11. Remove the strips and immediately make a PENCIL mark on each to show where the level of solvent stopped rising. Place the strips on a tray so they can dry overnight. 12. CLEANUP: Pour the solvent back into the solvent beaker. Rinse the tubes out. Return all your supplies to the supply table. DAY II: Identify Unknown Food Dyes 1.
There are only 7 different food dyes that have been approved for use in foods and drinks. Table 1 in the data section lists these 7 dyes and some important information that you will need in order to identify the dyes present in 2 flavors of Kool-Aid. 2. Look closely at your chromatography strips. The mixture of food dyes in your sample should now be separated. Because the food dyes have different chemical properties, each will dissolved in the solvent and move up the strip at different rates. How many different food dyes are present in each Kool-Aid flavor? (look closely: sometimes 2 dyes overlap and produce what may look like a 3rd dye).
Record the number of dyes present in Table 2. 3. In order to identify the food dyes in each Kool-Aid flavor, you will need 2 pieces of information: the color and Rf value of each dye. First, record the color of each separated dye in Table 2. 4. Now, calculate the Rf value for each separated dye as follows: a. Using a pencil, lightly draw a circle around the darkest area of color for each food dye (ignore the lighter color“tails”). b. Measure the distance (in cm) from the starting point (in the center of the line you drew) to the center of the circle you just drew (see drawing). Record this distance in Table 2. . Measure the distance (in cm) that the solvent moved (from the original line to the mark you made yesterday indicating where the solvent stopped rising – see drawing). Record this distance in Table 2. d. To calculate the Rf value, divide the distance the dye moved by the distance the solvent moved. Record this value in Table 2. 5. Using Table 1, identify specifically which dyes are present in grape and lemon-lime Kool-Aid. Record this in Table 2. 6. CLEANUP: Once you have collected all of your data, you may keep or throw away your chromatography strips. Return the rulers to the supply table. IV.
Data & Observations: Table 1: Colors and Rf values of 7 food dyes COLOR Rf FOOD DYE Blue 0. 8-1. 0 Blue #1 Blue 0. 45-0. 65 Blue #2 Bright pinkish-red 0. 5-0. 65 Red #3 Light red 0. 67-0. 85 Red #40 Yellow 0. 4-0. 7 Yellow #5 Orange 0. 8-0. 9 Yellow #6 Green 0. 65-0. 75 Green #3 Table 2: Food Dye Characteristics obtained from chromatography experiment Color of each Distance each Distance Rf of each Kool-Aid # of Dye Dye Moved Flavor Dyes Solvent Dye (cm) Moved (cm) Name of Dye Grape 1 2 3 1 2 3 LemonLime V. Analysis/Follow-Up Questions: 1. What food dyes were present in grape Kool-Aid? 2. What food dyes were present in lemon-lime Kool-Aid? . Scenario: You have a mixture of 2 food dyes (Red #3 and an unknown). You separate the two dyes using paper chromatography. The Rf value of the unknown dye is 0. 75. Would the unknown dye travel further than the Red #3 dye? Explain you answer. 4. Explain why it is important the mark the solvent level on the chromatography paper when you finished your experiment on Day 1. 5. Find 3 different food or drinks that contain artificial coloring. Read the nutrition label on each and complete Table 3 below. Table 3: Food Dyes Present in Various Food and Drink Samples Name of Food/Drink Brand Name Color Food Dyes Present