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Rf ratio and solvent distance
Why is the Rf value of a dye not affected by how far the solvent front is allowed to travel?
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Marking points
- 1 Explains that the spot-to-solvent distance ratio is constant, or that the two distances are directly proportional.
Full-mark answer
The dye spot and the solvent front travel proportional distances, so their distance ratio—the Rf value—remains constant.
Why this answer loses marks
The Rf value increases whenever the solvent is allowed to travel farther.
The spot also travels farther in proportion, so the distance ratio remains constant.