This common misconceptions covers Common Misconceptions within Chromatography for GCSE Chemistry. Revise Chromatography in Chemical Analysis for GCSE Chemistry with 23 exam-style questions and 15 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 8 of 13 in this topic. Use this common misconceptions to connect the idea to the wider topic before moving on to questions and flashcards.
⚠️ Common Misconceptions
Misconception 1: "The spot that travels furthest is the most concentrated"
Wrong. The distance a spot travels is determined by the substance's relative solubility in the solvent and its affinity for the paper — not by how concentrated it is. A very dilute solution of a highly soluble dye will still travel further than a concentrated solution of a less soluble dye. Spot intensity (darkness) is a rough guide to relative concentration, not travel distance.
Misconception 2: "One spot always means a pure substance"
One spot is strong evidence for purity, but it is not definitive. Two different compounds could happen to have the same Rf value in a particular solvent and appear as one spot. To confirm purity, you would need to run the chromatography in a different solvent — if the spot remains single, it is more likely to be pure.
Misconception 3: "Rf values can be greater than 1"
Impossible. A substance cannot travel further than the solvent that is carrying it. The Rf value is always between 0 and 1. If your calculation gives a value above 1, you have measured distances incorrectly — likely measuring substance distance from the wrong point.
Practice questions for Chromatography
What is the purpose of chromatography?
Explain how a chromatogram can be used to determine whether a substance is pure or a mixture.