RP6

Question 1

Why is it important to stop the chromatogram before the solvent front reaches the top of your chromatography paper?

Answer 1

The solvent will run off so the Rf value can’t be calculated

Question 2

Why is it important to mark positions in pencil rather than pen?

Answer 2

The pen ink would contain pigment which would dissolve in the solvent separating out, obscuring results

Question 3

Why is it important that the spot of plant extract is above the surface of the solvent when the chromatography plate is placed in the vial?

Answer 3

Would dissolve into the solvent .Solvent and sample would mix so could cause inaccurate results

Question 4

How could you modify the equipment/experiment, in order to get more accurate measurements of the Rf values for each pigment?

Answer 4

1. Measure in mm instead of in cm
2. Use longer paper
3. Increase the amount of time you wait before measuring

Question 5

Suggest why we should mark the spots immediately to calculate the Rf values.

Answer 5

The chromatograms will fade very quickly, particularly in the light

Question 6

Explain why it would be better to use Rf values rather than the distance moved by pigment spots?

Answer 6

The Rf value is constant/proportion so can compare whereas different distances may have been moved by both the solvent and pigment on the other chromatogram