In Rf calculation, which distance is the numerator?

In Rf calculation, which distance is the numerator?

• A. The distance traveled by the spot
• B. The distance traveled by the solvent front
• C. The distance from origin to the solvent front
• D. The distance traveled by the plate edge

Answer: (A)

In TLC, Rf is defined as the ratio of how far the compound’s spot moves to how far the solvent front moves. The numerator is the distance traveled by the spot itself, measured from the origin line to the center of the spot. The denominator is the distance traveled by the solvent front, measured from the origin to the leading solvent edge. This ratio is unitless and allows comparison across runs. For example, if the spot moved 2.0 cm and the solvent front moved 5.0 cm, Rf = 2.0 / 5.0 = 0.40. Other distances mentioned don’t represent the numerator: the distance moved by the solvent front is the denominator, the distance from origin to solvent front is the same solvent-front distance, and the distance traveled by the plate edge isn’t used in the Rf calculation.

In TLC, Rf is defined as the ratio of how far the compound’s spot moves to how far the solvent front moves. The numerator is the distance traveled by the spot itself, measured from the origin line to the center of the spot. The denominator is the distance traveled by the solvent front, measured from the origin to the leading solvent edge. This ratio is unitless and allows comparison across runs.

For example, if the spot moved 2.0 cm and the solvent front moved 5.0 cm, Rf = 2.0 / 5.0 = 0.40.

Other distances mentioned don’t represent the numerator: the distance moved by the solvent front is the denominator, the distance from origin to solvent front is the same solvent-front distance, and the distance traveled by the plate edge isn’t used in the Rf calculation.