STUDENT SPACE · TOPIC 5
Rf and colourless substances
Calculate Rf and explain how a locating agent reveals colourless substances.
The essentials
- Rf = distance travelled by the substance ÷ distance travelled by the solvent front, measured from the same baseline.
- Rf has no unit. Compare Rf values only under the same conditions.
- A locating agent can make colourless spots visible after the chromatogram has been developed and dried.
Key vocabulary
| English | Chinese |
|---|---|
| locating agent | 显色剂 |
| colourless | 无色的 |
| distance travelled | 移动距离 |
| Rf value | 比移值 |
Quick practice
A spot moves 2.4 cm while the solvent front moves 6.0 cm. Calculate its Rf.
Need a hint?
Divide the spot distance by the solvent-front distance.
Check your reasoning after trying
Rf = 2.4 ÷ 6.0 = 0.40. There is no unit.
Use Lesson 5 in your worksheet for written practice. Your teacher will discuss those answers in class.