Chromatography
Chromatography is a technique used to separate a mixture of soluble substances. It works by passing a solvent (the mobile phase) through a stationary phase (e.g., chromatography paper). Different components of the mixture travel at different speeds, causing them to separate out.
Full topic guide: the detailed syllabus page with worked examples and common mistakes lives at studyvector.co.uk/gcse/chemistry/chemical-analysis/chromatography.
Topic preview: Chromatography
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Topic explanation
Chromatography is a technique used to separate a mixture of soluble substances. It works by passing a solvent (the mobile phase) through a stationary phase (e.g., chromatography paper). Different components of the mixture travel at different speeds, causing them to separate out.
Chromatography is easiest to revise when it is treated as a precise exam behaviour, not a loose note-taking category. In GCSE Chemistry, the goal is to recognise how the topic appears in a question, identify the command word, and decide what evidence, method, or vocabulary earns marks. StudyVector keeps this page tied to AQA · Edexcel · OCR language where coverage is available, then routes practice towards the same topic so revision moves from explanation into retrieval.
A strong revision session starts with a short recall check. Write down the rule, definition, process, or method linked to Chromatography before looking at any notes. Then answer one exam-style prompt and compare your answer with the mark-scheme logic: did you make a clear point, support it with the right step, and avoid drifting into a nearby topic? This matters because many lost marks come from almost-correct answers that do not match the expected structure.
Use this guide as the first layer: understand the topic, look at the worked examples, complete the mini quiz, then move into full practice. The full StudyVector practice loop is designed to capture whether mistakes are caused by knowledge, method, language, or timing. That distinction is important. If the error is factual, you need reteaching. If the error is method-based, you need a worked retry. If the error is wording, you need command-word calibration. That is how Chromatography becomes a controlled revision target rather than another page in a folder.
Lost marks → repair task
Why marks are usually lost here
These are the error patterns StudyVector looks for after an attempt. The goal is not a generic explanation; it is one repair move and one follow-up question.
Unit, formula, or method slip
Examiner move: Select the correct method and keep units, substitutions, signs, and rounding visible.
Repair drill: Redo the calculation or method line slowly, naming the formula before substituting values.
Missing chain of reasoning
Examiner move: Show the link between point, method, evidence, and conclusion instead of jumping to the final line.
Repair drill: Write the missing because/therefore step, then retry one isomorphic question.
Command-word miss
Examiner move: Answer the action in the command word before adding extra detail.
Repair drill: 60-second rewrite: start the answer with explain, compare, evaluate, state, or calculate in mind.
Mini quiz
Use these checks before full practice. They test topic recognition, exam technique, and whether you can connect the explanation to a marked response.
1. What should you check first when a Chromatography question appears in GCSE Chemistry?
- A.The command word and the exact topic focus
- B.The longest paragraph in your notes
- C.A memorised answer from a different topic
2. Which revision action gives the strongest evidence that Chromatography is improving?
- A.Rereading the explanation twice
- B.Answering a timed exam-style question and reviewing lost marks
- C.Highlighting every key phrase in the topic notes
Sample questions
Topic-specific public question previews are still being reviewed. We keep them off public pages until the topic match is safe.
Exam tips
- Read the command word carefully — "explain" needs reasons; "state" expects a short fact.
- For Chromatography, show structured working even when you are practising multiple choice — it builds accuracy under time pressure.
- Mark yourself against the mark scheme style: one clear point per mark, in logical order.
- Come back to this topic after a day or two; short spaced reviews beat one long cram.
Worked examples
Example 1
Modelled exam response
In paper chromatography of ink, a spot of ink is placed on a pencil line on filter paper. The bottom of the paper is placed in a solvent. As the solvent moves up the paper, it dissolves the ink and carries it up. The different coloured dyes in the ink separate because they have different solubilities in the solvent and different attractions to the paper.
Example 2
Identify the task before answering
Question type: a Chromatography prompt asks for a clear response in GCSE Chemistry. Step 1: underline the command word. Step 2: name the exact part of Chromatography being tested. Step 3: decide whether the mark scheme wants a definition, method, explanation, comparison, or calculation. Why it works: most weak answers fail before the content starts because they answer the topic generally rather than the exact exam task.
Example 3
Turn feedback into a repair task
Suppose your answer shows partial understanding but loses marks for precision. First, rewrite the missing mark as a short target: "I need to state the mechanism, unit, reason, or evidence explicitly." Then answer one similar question without notes. Finally, compare the second attempt with the first and check whether the same mark was recovered. Why it works: Chromatography improves faster when feedback creates a specific retry, not another passive reading session.
Next revision routes from this subject
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Common mistakes
- Placing the starting line in the solvent at the beginning of the experiment. The baseline must be drawn in pencil and be above the solvent level, otherwise the sample will just dissolve in the solvent.
- Using a pen to draw the starting line. The ink from the pen will run and interfere with the results.
- Calculating the Rf value incorrectly. It is the distance moved by the spot divided by the distance moved by the solvent front, and it must be less than 1.
Exam board notes
Chromatography is a required practical for all exam boards. You must know the method for paper chromatography, be able to interpret a chromatogram, and calculate Rf values.
FAQs
What is the Rf value?
The Rf (retention factor) value is a ratio used to identify a substance in chromatography. It is calculated by dividing the distance the substance has moved from the baseline by the distance the solvent has moved from the baseline.
Why is the lid placed on the container during chromatography?
A lid is used to create a saturated atmosphere of the solvent vapour inside the container. This prevents the solvent from evaporating as it moves up the paper, which would affect the results.
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