Who this is for: Cambridge IGCSE Chemistry (0620) students who want chromatography — paper chromatography, Rf values and locating colourless substances — to become a reliable source of marks instead of a practical they only half-remember.
What query it owns: how to understand and revise chromatography in Cambridge IGCSE Chemistry.
Why this is safe: this page owns the chromatography revision-guide angle, while Tutopiya’s Chromatography subtopic page owns the learning resource and the free Chromatography quiz owns the practice.

Chromatography is one of the most frequently tested practical ideas in the Experimental Techniques and Chemical Analysis unit of Cambridge IGCSE Chemistry (0620). Whenever a question involves separating coloured mixtures, comparing dyes or calculating how far a substance has moved on chromatography paper, examiners expect you to know the setup, the meaning of Rf and how to interpret results. This guide explains exactly what chromatography covers, how to handle the question types that actually appear, and where to practise each skill.

Key takeaways

• Paper chromatography separates substances in a mixture because they have different solubilities in the solvent and different affinities for the paper.
• Rf value = distance moved by substance ÷ distance moved by solvent front — no units, always ≤ 1.
• The same substance gives the same Rf in the same solvent under the same conditions.
• Locating agents (e.g. iodine vapour, UV light) reveal colourless spots after the run.
• Draw the solvent front and baseline clearly before measuring distances.

What is chromatography in Cambridge IGCSE Chemistry?

Chromatography is a separation technique used to analyse mixtures, especially when the components are present in small amounts. In paper chromatography, a spot of mixture is placed on chromatography paper above the solvent level; as the solvent rises, each substance travels at a different rate. Cambridge IGCSE Chemistry (0620) tests the apparatus, how to calculate Rf, how to identify pure substances versus mixtures from the number of spots, and how to locate colourless compounds.

You can read the full explanation, worked examples and notes on Tutopiya’s Chromatography subtopic page before you attempt questions.

The core ideas you must master

These four ideas appear again and again. Learn what each one means and the exam phrasing that signals it.

Idea	What it means	How the exam uses it
Solvent front	Highest point reached by the solvent	”Measure from the baseline to the solvent front.”
Rf value	Ratio of distances (substance ÷ solvent)	“Calculate the Rf value of substance X.”
Pure vs mixture	One spot = pure; two or more = mixture	”State how many substances are present.”
Locating agent	Makes invisible spots visible	”Describe how to locate amino acids.”
Same Rf	Same substance in same solvent	”Explain whether A and B are the same dye.”

How to carry out paper chromatography — step by step

The safest method works for every describe question and Rf calculation.

1. Draw a pencil baseline near the bottom of the paper — ink would dissolve and smear.
2. Place a small spot of the mixture on the baseline; do not let the spot touch the solvent initially.
3. Pour solvent into the tank to a depth below the baseline; place the paper so the solvent rises past the spot.
4. Cover the tank to saturate the atmosphere and reduce evaporation at the edges.
5. Mark the solvent front when the run stops (before it reaches the top).
6. Locate spots — visible colours or a locating agent for colourless substances.
7. Measure distances from baseline to centre of each spot and to solvent front; calculate Rf.

Once you have worked through a few, test yourself with the free Chromatography quiz — it tells you fast whether the method has actually stuck.

Rf calculation vs interpretation: which approach does the question want?

Students lose marks by measuring from the wrong line or giving units for Rf.

Situation	What to do	Typical signal words
Calculate Rf	Substance distance ÷ solvent front distance	”Calculate the Rf value.”
Compare substances	Same Rf in same solvent → likely same substance	”Are dyes A and B the same?”
Identify purity	Count spots after one run	”State whether the sample is pure.”
Describe setup	Baseline above solvent, pencil line, covered tank	”Describe how to separate the inks.”
Colourless compounds	Name locating agent after run	”How would you locate the amino acids?”

Chromatography in past-paper wording: command words that matter

Most lost marks in chromatography questions come from misreading the command word or measuring from the wrong reference line.

Command word / phrase	What the question wants	Typical chromatography stem
Describe	Steps of the method or setup	”Describe how paper chromatography is used to separate the dyes.”
Calculate	Numerical Rf with working	”Calculate the Rf value of dye X.”
State	Short factual answer	”State what is meant by the solvent front.”
Explain	Reason linked to solubility/affinity	”Explain why the substances separate.”
Suggest	Apply to a new scenario	”Suggest why the Rf values would change in a different solvent.”

Worked exam-style stems (how to answer the wording)

Practising the wording — not just the formula — is what method marks reward.

1. “A dye moved 4.0 cm and the solvent front moved 10.0 cm. Calculate the Rf value.” Rf = 4.0 ÷ 10.0 = 0.40 (no units). Mark-scheme reward: correct ratio, no units stated.
2. “Two spots from different samples have the same Rf in the same solvent. What can you conclude?” They may be the same substance — same Rf in identical conditions is strong evidence, though not absolute proof without a reference. Reward: links same Rf to identity.
3. “Describe how to separate a mixture of food colourings by paper chromatography.” Pencil baseline; spot above solvent level; solvent rises; different dyes travel different distances; mark solvent front. Reward: baseline not in solvent, covered tank optional but creditworthy.

When you can recognise the wording instantly, work the full set on the Experimental Techniques topical past-paper questions and the Chromatography quiz to lock the method in.

How chromatography connects to the rest of Experimental Techniques

Chromatography sits alongside Separation and Purification, where filtration, distillation and crystallisation handle bulk separation. Identification of Ions and Gases follows when you need to confirm what a separated substance is. Paper 6 and the Alternative To Practical Skills unit often combine chromatography diagrams with analysis questions. When you are ready to mix topics, the Cambridge IGCSE Chemistry resource hub lets you move straight from a weak subtopic into the next.

Common mistakes students make

• Giving units for Rf (Rf is a ratio — no units).
• Measuring from the top of the paper instead of the solvent front.
• Letting the baseline dip into the solvent at the start, dissolving the spot.
• Using ink for the baseline instead of pencil.
• Saying chromatography separates by boiling point (that is distillation).

When you need more support

If chromatography questions keep tripping you up — especially Rf calculations and describe stems — work through the Experimental Techniques topical past-paper questions and the Chromatography quiz to pinpoint the exact gap, then get focused help from a Cambridge IGCSE Chemistry tutor to fix it quickly.

Frequently asked questions

Is chromatography hard in Cambridge IGCSE Chemistry? The setup is straightforward. Marks are lost when students give Rf units, measure from the wrong line or confuse chromatography with distillation.

What is the formula for Rf? Rf = distance moved by substance ÷ distance moved by solvent front. The value has no units and is always between 0 and 1.

How do you find colourless spots? Use a locating agent such as iodine vapour or ninhydrin for amino acids, or view under UV light if the substance fluoresces.

How do I revise chromatography effectively? Read the subtopic notes, practise Rf calculations on every diagram, then take the Chromatography quiz. Revisit describe questions before Paper 6.

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