Question about paper chromatography

Question

1. A pharmaceutical chemist runs a chromatography test on a substance and identifies two of its components by comparing their Rf values against certain standards. If two components have Rf values of 1.0 and 0.41, and the solvent front has travelled 12.0 cm from the sample's origin, what is the separation distance on the chromatogram?


2. A chemist performs an Rf calculation, obtains a value of 1.2, and decides that the answer is unacceptable. Why??

Answer 1

1.
Rf = (distance traveled by the spot) / (distance traveled by the solvent)
Then, (distance traveled by the spot) = (distance traveled by the solvent) x Rf

Distance traveled by the spot of the component with Rf 1.0
= 12 x 1
= 12 cm
Distance traveled by the spot of the component with Rf 0.41
= 12 x 0.41
= 4.92 cm

Distance between the spots of the two components
= 12 - 4.92
= 7.08 cm

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2.
In paper chromatography, the spots are carried upwards by the solvent.
Therefore, (distance traveled by the spot) ≤ (distance traveled by the solvent)

Rf = (distance traveled by the spot) / (distance traveled by the solvent)
Therefore, Rf ≤ 1.

It is impossible if Rf = 1.2 > 1.