chromatography of food colors vanderbilt student volunteers for science spring, 2007 training...
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Chromatography of Food Colors
Vanderbilt Student Volunteers for Science
Spring, 2007
Training Presentation
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Important!!!
• Please use this resource to reinforce your understanding of the lesson! Make sure you have read and understand the entire lesson prior to picking up the kit!
• We recommend that you work through the kit with your team prior to going into the classroom.
• This presentation does not contain the entire lesson—only selected experiments that may be difficult to visualize and/or understand.
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Pre-lab
• Use the scissors to cut the top off one Kool-Aid package of each color.
• Add one scoop of blue to the blue cups, one scoop of grape to the grape cups, and two scoops of orange to the orange cups.
• After you finish, roll the top of the package up and fasten with a piece of scotch tape.
• Take the brown food color from the #2 bag and add 2 to 4 drops to the 1-oz cup labeled brown.
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I. Introduction (p.2)• Ask: What is a mixture? a compound? How do you tell the
difference?– Both a mixture and a compound are combinations of substances. – The difference between them is that a mixture can be separated by
physical means and a compound can’t. • In a mixture each substance keeps its own properties.
– Write the formula for water on the board. (H2O) Explain that water is the combination of two elements: hydrogen and oxygen.
– Does water have the properties of oxygen and hydrogen? (no) – Can you separate water into hydrogen and oxygen?
• Not easily. It takes special equipment to separate water. Water is a compound, not a mixture.
• Ask: What substances make up a salad? How would you separate the mixture?– Salads are mixtures that are easy to separate. You simply take out the
lettuce, tomatoes, and carrots. You can physically separate the different substances.
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II. Check: Identifying mixtures and compounds (p.2)
Substance Mixture or compound? How to separate physically
• raisin bread mixture pick out the raisins and nuts with your hand
• sugar compound can’t separate (C12H22O11)
• salt water mixture filter the salt out of the water or evaporate the water
• salt compound can’t separate - NaCl
• hamburger mixture buns, lettuce, tomatoes,scrape off catsup, remove
meat
• rubbing alcohol compound can’t separate (C3H7OH)
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III. Demo: Separating colors (p.3) • Ask: Is green a pure color or a mixture of
colors? If so, how can we physically separate it?
– Record their ideas.
• Use a 16 oz. plastic cup, chromatography paper strip and a green marker.
• Pour a small amount of water in the bottom of the cup.
• Place a wooden stick across the top of the cup.
• Draw a line with the green marker just above the pencil mark on the chromatography strip.
• Fold the paper and hang it from the wooden stick as shown on the next page. Be sure the color line is above the water.
• In about 2-5 minutes the green should be separated into blue and yellow.
• Take the chromatography paper out of the water as soon as the separate colors can be seen.
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Explanation (p.3)• As the water travels to the top of the
paper, it dissolves the dyes in the pen.• Each dye travels at a different speed
depending on how strongly it is absorbed on the paper and how soluble it is in water.
– In this case the blue travels faster than the yellow.
• The retention factor (RF) of the dye is defined as the distance the dye moves divided by the distance traveled by the water.
• The retention factor of any dye is characteristic for a given combination of paper and solvent.
• For the same type of paper and solvent, and in the same time allowed, the blue and yellow dyes will always travel to the same position on the paper.
• We can use retention factors in experiments to help us identify unknown dyes. RF = distance dye moved /distance water moved
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IV. Chromatography of food colors--demo (p.4)
• Demonstrate the procedure first!• Show each student where to place the well
plates on the worksheet so they can tell what materials will be going into the wells.
• Add one scoop of each Kool Aid flavor to its own well and then add 2-4 drops of water to each well containing the Kool Aid.
• Use the dropper bottles of food colors to add 2 to 4 drops of food color to the appropriate well.
• Pick up the chromatography sheet they will be using and explain that they will be using a different toothpick to draw a line of each food color on one chromatography sheet and Kool-aid colors and brown food color on another chromatography sheet following the color and Kool-aid notations at the top of the two sheets.
• Using a different half toothpick each time, draw a line for each of the food colors on the one sheet by using a different toothpick for each color and drawing a line on the pencil line, following the color notation at the top of the chromatography sheet.
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IV. Chromatography of food colors (cont.)
• Gently wave the chromatography sheet to allow the colors to dry.
• Show the laminated chromatography sheet for both food colors and Kool-aid colors already drawn on the lines as an example
• Refold the chromatography sheet like an accordion so it stands in the cup.
• Remove the chromatography sheet and add the contents from the small bottle of water.
• Then place the chromatography sheet back in the cup, making sure the water is below the color lines.
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IV. Chromatography of food colors (cont.)
• Distribute the 24-well plates to the students and have each student add one scoop of Kool Aid to the appropriate well.
• Take the dropper bottles of food colors around to the student in each pair that has the food colors worksheet, and add 2 to 4 drops of food colors to the appropriate well in the well plate (blue, green, red, yellow for one student and brown for the other student.)
• While this is being done, tell students working with the Kool-Aid to add a few drops of water to each well containing Kool-Aid, using their water dropping bottle and stir with the toothpick.
• Use the toothpicks to draw a line of color on the pencil line on the student chromatography sheet.
• Use a different toothpick for each Kool-Aid solution.
• Dip the toothpick in the solution, then draw a line of that color on the pencil line on the chromatography sheet.
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IV. Chromatography of food colors (cont.)
• Gently wave the chromatography sheet to allow the
colors to dry.
• Refold the chromatography sheet like an accordion
so it stands in the cup. Remove the sheets from
the cups.
• Take out the 2 small bottles of water and add one
bottle to each of the 16-oz cups.
• Put each chromatography sheet in a cup. It doesn’t
matter if it rests against the edge.
• Make sure the water in the cup is below all the color
lines.
• The chromatography sheets should be left to
develop (about 20 minutes).
• While colors are separating, do the
chromatography skit and discuss retention
factors and the different food dyes.
• After the solvent front reaches the line drawn on the
chromatography sheet, remove the
chromatography sheet from the cup and place each
one on a sheet of paper towel to dry.
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IV. Chromatography of food colors (cont.)• Look at their food color
chromatography sheet and identify which of the food colors listed to the right are present.
• Refer to the Kool-aid ingredient sheets and show how to check for what food colors are present.
• Ask students to determine what colors are present in each of the Kool-aid chromatograms. These should be compared to the Kool-aid ingredient sheet.
• Finally, students should determine what food colors are present in the brown food color.
• Question: If you are allergic to yellow food colors, which of the Kool-aid flavors you’ve studied today might cause you to have an allergic reaction?
– Answer: Orange• Each student gets to keep their
chromatography sheet.
• Food Dyes. • The seven food colors approved by the
Food and Drug Administration are: – Red #3
– Red #40
– Yellow #5
– Yellow #6
– Blue # 1
– Blue #2
– Green #3.
• Only Red #3, Red #40, Yellow #5, Blue #1, and Green #3 are available in food color sets in grocery stores.
• Green #3, Yellow #6, and Blue #2 are not used very much in coloring food.
• Since Yellow #5 causes allergic reactions in some people, the FDA now requires that it be listed on food labels when it is used.