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Chalk It Up

Chromatography is the science of separation. The components to be separated are distributed between 2 phases; one is stationary while the other moves in a definite direction.

Materials needed

  • Box of white chalk
  • Assorted black markers with water-soluble nonpermanent ink (Sanford® and Crayola® brands work best.)
  • Watch glass
  • Forceps
  • Pipet
  • Filter paper
  • Ruler
  • A small beaker (less than 100 mL)
  • Water
  • Pencil
  • Scissors
  • Clock or watch

Prepare the chalk

  1. Stand a piece of chalk on end in the beaker. It must stand on end without falling over. If it does not, try the other end or another piece of chalk.
  2. Use the pencil to write an "x" on the upward-facing end of the chalk.
  3. Make a light pencil mark on the side of the chalk about 1" down from the upward-facing end.
  4. Remove the chalk from the beaker and set it aside.
  5. Fill the beaker with 3 mL of water and set it aside.

Prepare the marker solution

  1. Use the scissors to cut a section out of the filter paper about 1 cm x 3 cm in size.
  2. Select a marker and use it to color both sides of the filter paper so that no areas of white are showing.
  3. Place the colored filter paper in the center of the watch glass.
  4. Fill the pipet with 0.5 mL of water.
  5. Hold the paper in place with the forceps and carefully cover it with the water in the pipet.
  6. Stir the paper and water gently for 5 minutes with the forceps.
  7. Remove the paper from the watch glass and discard it.
  8. Hold the chalk vertically with the "x" end up and place it in the marker solution. The chalk should absorb all of the solution.
  9. Invert the chalk so that its inked end is up and hold it in that position.

Prime the chalk

  1. Fill the pipet with 0.5 mL of water from the beaker.
  2. Use the pipet to place 1 drop of water on the inked end of the chalk, being careful not to let it overflow the sides of the chalk. Allow the drop to soak in completely.
  3. Repeat step two 9 times.
  4. Stand the chalk on its inked end in the beaker. Again, the chalk must stand on end and not fall over.
  5. Observe the ink solution separate into bands of color as the water is drawn into the chalk.
  6. Allow the column to develop for 5-10 minutes or until the water reaches the pencil mark on the side of the chalk.
  7. Remove the chalk from the beaker.
  8. Record your observations.

More details

The discovery of chromatography is credited to the Italian-born Russian botanist Mikhail Tswett. Tswett discovered that he could extract the plant pigments that produce the fall colors in leaves by grinding the leaves in a solvent and pouring the resulting mixture through a tube full of powdered chalk (CaCO3, or calcium carbonate). The various pigments separated into colored bands as the mixture percolated down through the chalk. Tswett then carefully removed the column of chalk from the tube and separated the colored bands. Although he received some awards for his work, by the time he died in 1919 chromatography seemed to have made little impact. However, in the 1930s it was rediscovered and then spread worldwide.

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