NameDate_Block
Training Lab: Paper Chromatography
I.BackgroundInformation:
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 eateveryday.
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:• 1400ml beaker• 2q-tips
•1 strip ofchromatographypaper• Grape Kool-Aidsolution
•Peach MangoKool-Aidsolution• Solvent (alcohol, salt, & water)
•1pencil•ruler
III.Procedure:
DAY I: Separation of Chemicals
1.Cut 1 strip1 of chromatography paper so that it is about an inch longer than thebeaker.
2.Draw a straight line across the strip an inch above the bottom.
3.Label the top of the strip “Grape” and“Peach Mango.”
4.Use a q-tip to place a dot of grape Kool-Aid on the line under where you labeled grape. Do the same with the peach mangoKool-Aid.
5.Poke a wood splint through the opposite end of the strip. Use to hold strip in place.
6.Add a small amount (about 1/2 inch) of solvent to the beaker.
9.Lower the strip into a beaker 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. The solvent will begin to move up the strip, dissolve the food dyes, and carry themupwards.
10.Leave the strip in the beaker for 30minutes or until the solution line gets near the top of the beaker.
11.Remove the strip and immediately make a PENCIL mark to show where the level of solvent stopped rising. Place the strip on a watch glass so they can dryovernight.
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 ofKool-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 3rddye). Record the number of dyes present in Table2.
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 Table2.
4.Now, calculate the Rf value for each separated dye asfollows:
a.Using a pencil, lightly draw a circle around the darkest area of color for each food dye (ignore the lightercolor“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 Table2.
c.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 Table2.
d.To calculate the Rf value, divide the distance the dye moved by the distance the solvent moved. Record this value in Table2.
5.Using Table 1, identify specifically which dyes are present in grape and peach mango Kool-Aid. Record this in Table2.
6.CLEANUP: Once you have collected all of your data, you may keep or throw away your chromatography strips. Return the rulers to the supplytable.
IV. Data & Observations:
Table 1: Colors and Rf values of 7 food dyes
COLOR / Rf / FOOD DYEBlue / 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
Kool-Aid Flavor / # of Dyes / Color of each Dye / Distance each Dye Moved (cm) / Distance Solvent Moved (cm) / Rf of each Dye / Name of DyeGrape / 1
2
3
Peach Mango / 1
2
3
V.Analysis/Follow-UpQuestions:
1.What food dyes were present in grapeKool-Aid?
2.What food dyes were present in peach mango Kool-Aid?
3.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 youanswer.
4.Explain why it is important the mark the solvent level on the chromatography paper when you finished your experiment on Day1.
5.Find 3 different food or drinks that contain artificial coloring. Read the nutrition label on each and complete Table 3below.