chromatography

• In paper Chromatography, what is the stationary phase and what is the mobile phase?

  Stationary = paper

  mobile = Solvent (usually water or ethanol)
• How can chromatography show the difference between pure and impure substances?

  Pure ones will not separate into a number of spots
• How is the Rf value calculated?

  distance moved by spot/distance moved by solvent
• What does a substance's Rf value depend on?

  How soluble it is in the solvent and how attracted it is to the paper (or other stationary phase)
• In chromatography why must the solvent height be lower than the pencil line?

  So that the substances do not dissolve off the paper into the solvent
• Why do we use pencil rather than pen in the starting line?

  Pencil doesn't dissolve in the solvent. Therefore it won't run up the page.
• What does a higher RF value mean?

  The further up the chromatography paper the substances travelled
• What are the instructions for paper chromatography?

  -Draw a pencil line near the bottom of a sheet of filter paper

  -Add a spot of the ink to the line and place the sheet in the beaker of solvent (the solvent depends on what is being tested)

  -Make sure the ink isn't touching the solvent

  -Place a lid on top to stop evaporation

  -As the solvent goes up the paper the ink will move

  -Each different dye will move at a different rate and seperate out

  -if any of the dyes in the ink are insoluble they'll stay on the baseline

  -When the solvent has nearly reached the top take the paper out

  -The end result is a chromatogram