What effect on the Rf value of the compound would be observed if the developing jar had been inadvertently wet (with water) (Manual p 5)? Why?

 

  • What is the purpose of treating your spinach with methanol prior to extraction?
  • You are using light petroleum to extract the organic components of your spinach sample. Why does the extraction solvent also contain methanol?
  • If you placed some light petroleum and some water in a separating funnel, you would get two layers. Which layer would be on the top and why (Hint: see Manual p 8)?
  • By considering their structures (Manual p 2), explain why β-carotene has a higher Rf than xanthophyll.
  • Delete the appropriate (bold) words to complete the following:

    If the solvent is more polar than the sample, then the sample/solvent binds more strongly to the polar adsorbent of the TLC plate than the sample/solvent, thus the sample ascends the TLC plate quickly/slowly.

  • If a compound has an Rf value of 0.5 using 50% dichloromethane/50% light petroleum as eluting solvent, will it then have an Rf value greater or less than 0.5 if the following solvents were used as eluants (Manual p 5):
    1. a)  80% dichloromethane / 20% light petroleum
    2. b)  100% light petroleum
  • What effect on the Rf value of the compound would be observed if the developing jar had been inadvertently wet (with water) (Manual p 5)? Why?

 

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