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What is the purpose of treating your spinach with methanol prior to extraction?

  1. You are using light petroleum to extract the organic components of your spinach sample. Why does the extraction solvent also contain methanol?
  2. 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)?
  3. By considering their structures (Manual p 2), explain why β-carotene has a higher Rf than xanthophyll.
  4. 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.
  5. 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
  6. 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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