chromatography

• What is the method for carrying out paper chromatography?

  1. Draw a horizontal pencil line on chromatography paper.
  2. Mark five pencil spots at equal spaces across the line.
  3. Use a capillary tube to place spots of known and unknown food colors.
  4. Pour water into a beaker to a depth of 1 cm.
  5. Attach the paper to a glass rod and lower it into the beaker.
  6. Ensure the pencil line is above the water surface.
  7. Remove the paper when the water has traveled 3/4 up.
  8. Mark the water's reach and hang the paper to dry.
• What is the purpose of the capillary tube in paper chromatography?

  To put a small spot of each food color onto the pencil spots
• Why is it important to keep the spots of food coloring small?

  To prevent the colors from spreading into each other
• What is used as the solvent in the paper chromatography experiment?

  Water
• What happens if the pencil line touches the water in the chromatography experiment?

  The water will wash the ink off the line
• Why do we usually put a lid on the beaker during chromatography?

  To reduce evaporation of the solvent
• When should the paper be removed from the beaker?

  When the water has traveled around 3/4 up the paper
• What does it indicate if the unknown color separates into three spots?

  It is a mixture of three colors
• How can you determine which known colors are in the unknown color?

  By comparing the spots in the unknown color with the known colors
• What is the purpose of calculating RF values in chromatography?

  To identify the chemicals in the colors
• How do you calculate the RF value for a chemical?

  By dividing the distance moved by the chemical by the distance moved by the solvent
• What is the RF value for the chemical in color A if the distance moved is 14 mm and the solvent moved 70 mm?

  $RF =$$\frac{14 \text{ mm}}{70 \text{ mm}} =$$0.2$
• What should you do if the RF value of a chemical is not found in the database?

  You need to carry out further analysis to identify it
• What are the key points to remember during the chromatography process?

  • The pencil line must be above the water surface.
  • The sides of the paper must not touch the beaker walls.
  • A lid should be placed on the beaker to reduce evaporation.