2: Chromatography Flashcards Preview

IB Biology SL > 2: Chromatography > Flashcards

Flashcards in 2: Chromatography Deck (6)
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1
Q

How could we separate photosynthetic pigments?

A

with chromatography

  • paper chromatography used in class
  • thin layer chromatography is better
2
Q

Describe method for chromatography (first 4 steps).

A
  1. tear up leaf into small fragments
  2. grind pieces of leaf with sharp sand and propanone to extract leaf pigments
  3. transfer sample of extract to a watch glass
  4. evaporate to dryness with hot air from hair-dryer
3
Q

Describe method for chromatography (second 4 steps).

A
  1. add a few drops of propanone to dissolve the pigments
  2. build up a concentrated spot of pigment 10mm from the end of the strip of paper/TLC strip
  3. suspend the strip in a tube with the base dipping into running solvent
  4. remove the strip from the tube when the solvent has nearly reached the top (of strip)
4
Q

What is the Rf value? Describe method for calculating Rf value.

A

Rf = ratio of the distance traveled by a compound to that of the solvent front

Rf = distance moved by spot (a pigment) / distance moved by solvent

5
Q

Why do pigments separate in chromatography?

A

because of their varying solubility in the running solvent

6
Q

State 4 main pigments and their approximate Rf values.

A
  1. carotene (0.9)
  2. chlorophyll a (0.65)
  3. chlorophyll b (0.6)
  4. xanthophylls (0.3-0.5)

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