Required Practicals

Question 1

Describe how to produce a chromatogram of chlorophyll pigments (6)

Answer 1

1. Draw a straight line in pencil 1cm above bottom of filter paper
   * don’t use pen
2. Cut section of leaf and place in mortar, add 20 drops of acetone and grind with pestle to release pigments
3. Use a capillary tube to extract some pigment and blot it onto centre of drawn pencil line
4. Suspend chromatography paper in solvent so level of liquid is below pencil line and leave until solvents travels near to the top
5. Remove paper from solvent and draw line where solvent moves up to (pigments should have separate sources and should be different spots at different heights)
6. Calculate Rf value for each spot

Question 2

Rf value equation

Answer 2

Distance travelled by dye/distance travelled by solvent

Question 3

What to remember about measuring distance of blobs in chromatography?

Answer 3

Always measure distance from centre of the blob

Question 4

How would you use the Rf values of the different pigments to identify each pigment?

Answer 4

Compare to known Rf values in a database

Question 5

When comparing Rf values to a known database, what must you make sure?

Answer 5

Make sure they are for paper chromatography and use the same solvent

Question 6

Pigments that travel further up the paper have…

Answer 6

A HIGHER Rf value

Question 7

What factors affect the rate of mobility of the pigment in chromatography?

Answer 7

Affinity - lower affinities travel further up paper

Solubility - more soluble travel faster and further up paper (end up closer to the top at the solvent front)