Thin-layer chromatography
Cambridge A-Level Chemistry (9701) · Unit 37: Analytical techniques (A Level) · 10 flashcards
Thin-layer chromatography is topic 37.1 in the Cambridge A-Level Chemistry (9701) syllabus , positioned in Unit 37 — Analytical techniques (A Level) . In one line: The stationary phase is the solid material on which the separation occurs in TLC. It is typically a thin layer of a substance like aluminium oxide (Al₂O₃) or silica gel supported on a glass or plastic plate.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 10 flashcards — 6 definitions and 4 key concepts — covering the precise wording mark schemes reward. Use the 6 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Some cards in this deck are on other syllabus topics: 37.2 Gas / liquid chromatography. Each card is labelled with its topic.
The term 'stationary phase' in the context of thin-layer chromatography (TLC). Give an example
The stationary phase is the solid material on which the separation occurs in TLC. It is typically a thin layer of a substance like aluminium oxide (Al₂O₃) or silica gel supported on a glass or plastic plate.
What the Cambridge 9701 syllabus says
2025-2027 syllabus, in our words · A2 LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Describe and understand these thin-layer chromatography terms: (a) stationary phase, for instance aluminium oxide held on a solid support; (b) mobile phase, which is a solvent that may be polar or non-polar; (c) Rf value; (d) baseline and solvent front.
- Interpret Rf values.
- Explain why Rf values differ, in terms of how strongly substances interact with the stationary phase and how soluble they are in the mobile phase.
Also in this deck: 37.2 Gas / liquid chromatography
- Describe and understand these gas/liquid chromatography terms: (a) the stationary phase, a non-polar liquid of high boiling point held on a solid support; (b) the mobile phase, a gas that does not react; (c) retention time.
- Interpret a gas/liquid chromatogram to find what percentage of a mixture each component makes up.
- Explain differences in retention time by how strongly each component interacts with the stationary phase.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9701 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Topic 37.1 · Thin-layer chromatography
Define the term 'stationary phase' in the context of thin-layer chromatography (TLC). Give an example.
The stationary phase is the solid material on which the separation occurs in TLC. It is typically a thin layer of a substance like aluminium oxide (Al₂O₃) or silica gel supported on a glass or plastic plate.
Topic 37.1 · Thin-layer chromatography
Define the term 'mobile phase' in the context of thin-layer chromatography (TLC). What is its role?
The mobile phase is the solvent that moves through the stationary phase in TLC, carrying the compounds to be separated. Its polarity influences the relative solubility and movement of different compounds.
Topic 37.1 · Thin-layer chromatography
Define the Rf value in thin-layer chromatography (TLC).
The Rf value (retardation factor) is the ratio of the distance traveled by the compound to the distance traveled by the solvent front in TLC. Rf = (distance traveled by compound) / (distance traveled by solvent front).
Topic 37.1 · Thin-layer chromatography
Explain how the interaction with the stationary phase affects the Rf value of a compound in TLC.
Stronger interactions with the stationary phase result in a smaller Rf value, as the compound spends more time adsorbed to the stationary phase and travels a shorter distance up the plate. Weaker interactions lead to higher Rf values.
Topic 37.1 · Thin-layer chromatography
Explain how the relative solubility of a compound in the mobile phase affects its Rf value in TLC.
Greater solubility in the mobile phase leads to a larger Rf value. The compound is more readily dissolved and carried further up the TLC plate by the solvent.
Topic 37.2 · Gas / liquid chromatography
Describe the stationary phase in gas-liquid chromatography (GLC).
In GLC, the stationary phase is a high-boiling point, non-polar liquid coated on an inert solid support (
Topic 37.2 · Gas / liquid chromatography
Describe the mobile phase in gas-liquid chromatography (GLC).
The mobile phase in GLC is an unreactive carrier gas, such as helium or nitrogen. It's role is to transport the vaporized sample through the column without interacting with it.
Topic 37.2 · Gas / liquid chromatography
Define 'retention time' in gas-liquid chromatography (GLC).
Retention time is the time it takes for a particular compound to travel from the injection point to the detector in GLC. It is used to identify compounds.
Topic 37.2 · Gas / liquid chromatography
How can you interpret a gas/liquid chromatogram to determine the percentage composition of a mixture?
The area under each peak in a GLC chromatogram is proportional to the amount of that component in the mixture. The percentage composition is determined by calculating the percentage of each peak area relative to the total area of all peaks.
Topic 37.2 · Gas / liquid chromatography
Explain how interaction with the stationary phase affects retention times in gas-liquid chromatography (GLC).
Compounds with stronger interactions with the stationary phase will have longer retention times, as they spend more time dissolved in the liquid phase and are therefore slower to pass through the column. Weaker interactions result in shorter retention times.
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