In chromatography, how does the Rf value relate to movement?

In chromatography, how does the Rf value relate to movement?

• A. Higher Rf means slower movement
• B. Higher Rf means faster movement
• C. Rf is always equal to 1
• D. Rf is a measure of color intensity

Answer: (B)

In chromatography the movement of a substance is described relative to how far the solvent front travels. The Rf value is a ratio: distance moved by the substance divided by distance moved by the solvent front. Because it’s a ratio to the solvent front, a substance that follows the solvent more closely (moves further relative to the front) gives a larger Rf. So a higher Rf means the substance moved faster relative to the solvent front. For example, if the solvent front moves 10 cm and the substance moves 7 cm, the Rf is 0.7, indicating fairly rapid movement. If it only moves 1 cm, the Rf is 0.1, indicating slow movement. Rf values typically range from 0 to 1. This is not about how intense the color is, and it’s not always 1. It’s also not indicating slower movement when Rf is higher.

In chromatography the movement of a substance is described relative to how far the solvent front travels. The Rf value is a ratio: distance moved by the substance divided by distance moved by the solvent front. Because it’s a ratio to the solvent front, a substance that follows the solvent more closely (moves further relative to the front) gives a larger Rf. So a higher Rf means the substance moved faster relative to the solvent front.

For example, if the solvent front moves 10 cm and the substance moves 7 cm, the Rf is 0.7, indicating fairly rapid movement. If it only moves 1 cm, the Rf is 0.1, indicating slow movement. Rf values typically range from 0 to 1.

This is not about how intense the color is, and it’s not always 1. It’s also not indicating slower movement when Rf is higher.