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Imagine a researcher allowed the paper chromatogram to develop for far longer than necessary in the mobile phase, such that the solvent front ran into the top edge of the paper and the spots continued to move. Would the resulting Retention Factors (Rf) be overestimated, underestimated or remain unaffected? Explain your reasoning.

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Answer:

The resulting Retention Factors (Rf) would be overestimated

Explanation:

A Retention Factor (Rf) is calculated from the division of the distance of a spot (A) by the distance of the solvent front (B).

  • Rf = A/B

Let's assume we have a paper with 10 cm of lenght. In that in a normal experiment, the solvent front is at the 8cm mark, while the spot is at the 4cm mark. Thus the Rf is 0.5. However, if we let the solvent front run into the top edge of the paper, B will always be 10cm, while A keeps increasing. For instance, after a while B would be 10 cm while A is 7 cm, resulting in a Rf of 0.7. This means that the Rf was overestimated.

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