paper chromatography

• paper chromatography separates soluble substances in a mixture
• METHOD

  1. on chromatography paper, draw the base line with a pencil 1.5cm from the bottom
  2. drop the ink onto the paper in a dot using a capillary tube
  3. put 1cm solvent (water or ethanol) into the beaker
  4. place the paper in the beaker, ensuring the solvent does not touch the base line
  5. place lid on beaker to stop evaporation
  6. wait for the solvent to seep up to nearly the top of the paper
  7. take paper out and leave to dry
  8. the pattern left is called a chromatogram
  9. calculate Rf value
• mobile phase - thing the molecules can move in (solvent)
• stationary phase - thing molecules cant move in (paper)
• insoluble substances stay at the base line
• more soluble substances move higher up the paper as they spend more time in the mobile phase so move quicker
• less soluble substances spend more time in the stationary phase because e they are more attracted to it, meaning they don't move as far as they travel at a slower rate
• Rf = distance travelled by the substance /

  distance travelled by the solvent
• pure substance - only one dot travels up the paper
• mixture - multiple dots travel up the paper