Required Practical 7- Chromatography on leaf pigments

Question 1

Rf value?

Answer 1

Distance travelled by spot/distance travelled by solvent front

Question 2

Why are pigment spots measured from centre?

Answer 2

-average distance
-standardise readings
-allow comparisons to be made

Question 3

Why is pencil used rather than pen?

Answer 3

Ink in pen may dissolve in solvent- interfere with chromatogram

Question 4

Why is it important to allow each pigment to dry before applying next?

Answer 4

Drop could expand too much and blur separation

Question 5

Why must pigment spot be above solvent level?

Answer 5

Pigment doesn’t wash off (dissolve into solvent)

Question 6

Solvent front marked immediately after chromatogram complete?

Answer 6

Solvent front impossible to see once solvent evaporated

Question 7

Better to compare Rf values rather than distance moved by pigment?

Answer 7

Fr value ratio- remains constant for pigments
-allows comparisons to be made
-solvents can travel different distances

Question 8

Important not to move boiling tube?

Answer 8

Prevent solvent splashing up and distorting/diluting spits formed by samples