Chemistry 0620 · syllabus 12.1, 12.3, 12.4
Cambridge IGCSE Chemistry 0620 — Separation and chromatography topical past papers
Choosing apparatus, separating mixtures by filtration, crystallisation and distillation, judging purity from melting points, and paper chromatography with Rf values.
- Questions
- 452
- Years
- 2009–2026
- With mark scheme
- 98%
- Questions 2022–2026
- 141
Anyone can browse these pages. Opening the questions and their mark schemes takes a free Momentum account.
What Separation and chromatography covers
Practical chemistry starts with the right apparatus: a stop-watch for time, a thermometer for temperature, a balance for mass, and for volume a measuring cylinder, a burette, a volumetric pipette for one fixed volume, or a gas syringe for a gas. It also has its own vocabulary. A solvent dissolves a solute to make a solution, and a saturated solution holds as much solute as it can at that temperature; the residue is what is left behind by filtration, evaporation or distillation, and the filtrate is the liquid that passes through the filter paper. You are asked to suggest the advantages and disadvantages of methods and apparatus, not only to name them.
Mixtures are separated by using a difference between their parts. A suitable solvent dissolves one substance and leaves another; filtration removes an insoluble solid from a liquid; crystallisation recovers a dissolved solid by heating the solution until crystals start to form and then letting it cool; simple distillation recovers the solvent from a solution; and fractional distillation separates miscible liquids with different boiling points, such as ethanol and water. A pure substance melts and boils at fixed temperatures, while impurities lower the melting point, raise the boiling point and make either change happen over a range of temperatures.
Paper chromatography separates soluble substances. Spots are placed on a pencil baseline above the level of the solvent, and each substance travels a different distance up the paper as the solvent rises. Comparing the spots with known substances identifies the unknown, and a pure substance gives a single spot. On the Extended route a locating agent reveals colourless substances, and you calculate Rf = distance travelled by the substance ÷ distance travelled by the solvent, a value that identifies a substance in a given solvent. Separation, purity and chromatography are standard contexts in the practical papers.
In the syllabus
The headings this topic has in the Cambridge International 2026–2028 syllabus, as the board prints them.
- 12.1 Experimental design
- 12.3 Chromatography
- 12.4 Separation and purification
What you should be able to do
- Name suitable apparatus for measuring time, temperature, mass and volume, and suggest advantages and disadvantages of methods
- Use the terms solvent, solute, solution, saturated solution, residue and filtrate correctly
- Choose and describe a separation method: a solvent, filtration, crystallisation, or simple or fractional distillation
- Use melting and boiling points to identify a substance and judge whether it is pure
- Describe paper chromatography and interpret a chromatogram to identify substances and judge purity
- Use a locating agent for colourless substances and calculate Rf values (Extended)
Key ideas
- Rf = distance travelled by substance ÷ distance travelled by solvent, a number between 0 and 1 with no units
- A pure substance has a sharp, fixed melting point and boiling point; impurities lower the melting point and raise the boiling point
- Fractional distillation separates miscible liquids by their boiling points; simple distillation separates a solvent from what is dissolved in it
- Filtration separates an insoluble solid, the residue, from a liquid, the filtrate
- A volumetric pipette measures one fixed volume accurately; a burette delivers a measured, variable volume; a measuring cylinder is quicker but less accurate
How Separation and chromatography has been examined
From 2022 to 2026, Separation and chromatography was on Paper 3 · Theory (Core) in 9 of 14 exam series, worth about 6% of that paper’s marks.
| Paper | Questions | Share of marks | Series |
|---|---|---|---|
| Paper 1 · Multiple Choice (Core) | 48 | 4% | 14 of 14 |
| Paper 2 · Multiple Choice (Extended) | 45 | 4% | 14 of 14 |
| Paper 3 · Theory (Core) | 17 | 6% | 9 of 14 |
| Paper 4 · Theory (Extended) | 10 | 5% | 6 of 14 |
| Paper 6 · Alternative to Practical | 21 | 11% | 11 of 14 |
Momentum’s own count, over the questions in its bank for these years: a series is one exam session, every zone included, and a question filed under two chapters counts in both. Median marks per question: 1.
Filed in Momentum under: Separating Substances.
A worked example
A food dye is tested by paper chromatography beside two known dyes, P and Q. The solvent front is 8.0 cm above the baseline. The food dye gives two spots, 2.0 cm and 4.8 cm from the baseline; P gives one spot at 2.0 cm and Q one at 6.0 cm. Calculate the Rf values of the food dye's spots and say what the results show.
- Rf = distance moved by the spot ÷ distance moved by the solvent
- First spot: 2.0 ÷ 8.0 = 0.25; second spot: 4.8 ÷ 8.0 = 0.60
- P: 2.0 ÷ 8.0 = 0.25, the same as the first spot, so the food dye contains P
- Q: 6.0 ÷ 8.0 = 0.75, which matches neither spot, so the food dye does not contain Q
- There are two spots, so the food dye is a mixture of at least two substances, one of which is neither P nor Q
Answer: Rf values 0.25 and 0.60; the food dye is a mixture containing P and another substance that is not Q
Written by Momentum for this page, with its own numbers; it is not taken from a past paper.
Mistakes that cost marks
- Drawing the baseline in ink — ink is a mixture of dyes that dissolves and runs up the paper; a pencil line stays where it is
- Setting the baseline below the solvent level — the spots dissolve into the solvent in the container instead of moving up the paper
- Measuring the solvent distance to the top of the paper — it runs from the baseline to the solvent front, which must be marked as soon as the paper is taken out
- Choosing simple distillation for two miscible liquids — liquids such as ethanol and water need fractional distillation to separate them by boiling point
- Saying an impure solid has a higher melting point — impurities lower the melting point and make the solid melt over a range of temperatures
Exam technique
- For 'suggest a method', identify the property that differs — solubility, boiling point, or whether a solid is dissolved — and name the method that uses it
- Describe a separation as a sequence: what is added, what is heated or filtered, and what is collected where
- Show both distances in an Rf calculation and give the value to two decimal places, then compare it with the known values
- When reading a chromatogram, count the spots to judge purity, and match an unknown only to a known substance whose spot has travelled the same distance in the same solvent
Practising in Momentum
- Every question in a chapter as one list, from every paper and year in the bank, newest first or shuffled.
- Each question turns over to its own part of the mark scheme, where the board published one.
- Narrow by paper, year, session, zone and marks, and star the questions worth keeping.
- Pick chapters, a number of questions and a time, and the exam builder draws a mock to sit and mark.
Past-paper questions and mark schemes are the copyright of Cambridge International. Momentum shows them to signed-in learners for revision and does not publish them on these pages.