chromatography

• What is the purpose of paper chromatography?

  To identify substances in a mixture
• What are the four methods scientists use to separate mixtures?

  • Filtration
  • Crystallization
  • Distillation (simple and fractional)
  • Chromatography
• What does chromatography allow us to separate substances based on?

  Different solubilities
• How do you set up a paper chromatography experiment with colored pens?

  Draw a pencil line, place dots of colors, and put the paper in a solvent
• What is the name of the paper used in chromatography?

  Chromatography paper
• What do we call the solvent in chromatography?

  The mobile phase
• What does a single spot on chromatography paper indicate about a color?

  It indicates that the color is a pure compound
• What do we call the paper in chromatography?

  The stationary phase
• What happens to a more soluble substance in chromatography?

  It travels further up the paper
• Why do we draw the starting line in pencil in chromatography?

  Because pen would move with the solvent
• How can paper chromatography be used to identify an unknown substance?

  • Place a dot of the unknown on the pencil line
  • Measure the distance moved by the substance and the solvent
  • Calculate the RF value using the formula:

  $RF =$$\frac{\text{distance moved by substance}}{\text{distance moved by solvent}}$

  • Compare the RF value with a database
• What is the formula to calculate the RF value in chromatography?

  $RF =$$\frac{\text{distance moved by substance}}{\text{distance moved by solvent}}$
• If a substance moved 44 mm and the solvent moved 75 mm, what is the RF value?

  $RF =$$\frac{44 \text{ mm}}{75 \text{ mm}} =$$0.57$
• What should you do if the RF value of a substance is not found in the database?

  Repeat the experiment with a different solvent
• What are the characteristics of a pure compound in chromatography?

  • Produces a single spot in all solvents
  • Does not separate into different spots
• What happens to the position of a spot when a different solvent is used in chromatography?

  • The position of the spot may change
  • The number of spots remains the same for pure compounds