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Chromatography: A Separating Process

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Author: Janice VanCleave

The color of many things is actually a combination of color pigments. When the pigments are physically mixed together, but their atoms and molecules are not combined, the different pigments can often be separated. The separation of the pigments is achieved by a process called chromatography.

In this project, you will test different methods of chromatography. You will also determine the effects of various absorbencies of materials on color separation and measure the flow rate of color pigments.

Getting Started

Purpose: To calculate the flow rate for a yellow food dye.

Materials

  • color-coated candies (such as M&Ms™)
  • baby-food jar
  • distilled water
  • marking pen
  • masking tape
  • scissors
  • ruler
  • coffee filter
  • pencil
  • toothpick
  • drinking straw
  • drinking glass
  • paperclip
  • water
  • 2-liter plastic soda bottle with cap

Procedure

  1. Place ten yellow-colored candies in the baby-food jar.
  2. Add enough distilled water to cover the candies.
  3. Gently shake the jar until the yellow color on each candy is removed. Dissolve as little of the white undercoating on the candies as possible.
  4. Remove and discard these candies. Keep the yellow liquid.
  5. Add ten more yellow-colored candies to the yellow liquid in the jar.
  6. Again, gently shake the jar until the yellow color on each candy is gone. Remove and discard these candies. Keep the yellow liquid.
  7. With the marking pen, write "Yellow Food Dye" on a piece of masking tape and tape this label to the jar.
  8. Cut a strip about 11/2 inches (3.8 cm) wide and 6 inches (15 cm) long from the coffee filter.
  9. Cut a point at one end of the paper strip.
  10. Draw a faint pencil line across the pointed end of the paper strip. Use the pencil to label the line "Start."
  11. Draw a second pencil line 4 inches (10 cm) above the Start line. Label this second line "End."
  12. With the end of the toothpick, transfer a drop of the yellow dye to the center of the start line.
  13. Allow the dot of dye to dry before depositing another drop of dye on the same spot.
  14. Place ten more drops of dye on the same spot, but allow each dot to dry before adding a new one. Note: You want a dark, heavy coating of the yellow pigment on the paper strip.
  15. Wrap the even end of the paper strip around the straw.
  16. Place the pointed end of the paper strip into the empty glass. Adjust the paper strip so that the point barely touches the bottom of the glass when the straw is resting across the top of the glass.
  17. Paper clip the strip around the straw (see Figure 16.1).
  18. Remove the strip from the empty glass.
  19. Pour water into the glass to a depth of 1/2 inch (1.8 cm).
  20. Return the paper strip to the glass, resting the straw across the top of the glass. Note: The point of the paper strip should touch the water, but the yellow dot must be above the water level.
  21. Cut off the bottom of the plastic soda bottle.
  22. Secure the cap on the bottle and set the bottle over the glass with the paper strip (see Figure 16.2).
  23. Watch the water rise up the paper strip. At the instant the water reaches the top line, remove the strip and allow it to dry.
  24. Measure the distance from the start line to the center of the color band formed.
  25. Chromatography: A Separating Process

  26. Use the following equation to calculate the flow rate (R) for the yellow dye. See Appendix 9 for an example calculation.
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