Who this is for: Cambridge IGCSE Chemistry (0620) students who want separation and purification — filtration, crystallisation, simple and fractional distillation — to become a reliable source of marks instead of a list of methods they mix up under pressure.
What query it owns: how to understand and revise separation and purification in Cambridge IGCSE Chemistry.
Why this is safe: this page owns the separation and purification revision-guide angle, while Tutopiya’s Separation and Purification subtopic page owns the learning resource and the free Separation and Purification quiz owns the practice.

Separation and purification is one of the highest-frequency practical topics in Cambridge IGCSE Chemistry (0620). Examiners routinely ask which method suits a given mixture — sand and water, salt solution, crude oil fractions — and expect precise vocabulary: residue, filtrate, distillate, fractionating column. This guide explains exactly what each technique does, how to choose the right method, and where to practise each skill.

Key takeaways

• Filtration separates an insoluble solid from a liquid; the solid is the residue, the liquid passing through is the filtrate.
• Crystallisation obtains a soluble solid from solution by evaporating solvent and allowing crystals to form on cooling.
• Simple distillation separates a solvent from a dissolved solid or collects a single liquid with a fixed boiling point.
• Fractional distillation separates liquids with different boiling points using a fractionating column.
• Match the method to the type of mixture — insoluble solid, soluble solid, liquid mixture or immiscible liquids.

What is separation and purification in Cambridge IGCSE Chemistry?

Separation and purification techniques recover pure substances from mixtures. Cambridge IGCSE Chemistry (0620) covers filtration, crystallisation, simple distillation, fractional distillation and decanting where appropriate. Questions test apparatus diagrams, the reason each method works, and which technique to select for a described mixture such as copper sulfate crystals from solution or ethanol from water.

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

The core ideas you must master

These five 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
Filtration	Insoluble solid trapped on filter paper	”Separate sand from water.”
Crystallisation	Soluble solid from saturated solution	”Obtain pure copper sulfate crystals.”
Simple distillation	Boil and condense one volatile component	”Obtain water from salt solution.”
Fractional distillation	Separate liquids by boiling point	”Separate ethanol from water.”
Residue / filtrate	Solid left behind / liquid collected	”Name the filtrate.”

How to choose the right separation method — step by step

The safest approach is to classify the mixture first, then name the technique.

1. Identify the phases — solid and liquid? two liquids? dissolved solid in water?
2. Ask if the solid dissolves — insoluble → filtration; soluble → crystallisation or evaporation to dryness (crystallisation preferred for hydrated salts).
3. For liquids, check boiling points — large difference and one component needed → simple distillation; close boiling points → fractional distillation.
4. Name apparatus — condenser, fractionating column, evaporating dish as appropriate.
5. State what is collected — filtrate, distillate, crystals.

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

Filtration vs distillation vs crystallisation: which method applies?

Students lose marks by naming the wrong technique or confusing residue with filtrate.

Mixture type	Best method	Typical signal words
Insoluble solid + liquid	Filtration	”sand and water”, “chalk and water”
Soluble solid + water	Crystallisation	”pure crystals from solution”
Solvent from solution	Simple distillation	”obtain the water from seawater”
Two miscible liquids	Fractional distillation	”separate petrol fractions”, “ethanol and water”
Immiscible liquids	Separating funnel	”oil and water”

Separation and purification in past-paper wording: command words that matter

Most lost marks come from vague describe answers or choosing distillation when filtration is enough.

Command word / phrase	What the question wants	Typical separation stem
Name the method	State the technique only	”Name a method to separate iron filings from sulfur.”
Describe	Steps or apparatus setup	”Describe how to obtain pure sodium chloride crystals.”
Explain	Why the method works	”Explain how fractional distillation separates crude oil.”
State	Vocabulary or product	”State what is meant by the distillate.”
Suggest	Method for a new mixture	”Suggest how to separate a mixture of ethanol and water.”

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

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

1. “Describe how to obtain pure copper sulfate crystals from copper sulfate solution.” Heat to evaporate some water to concentrate; leave to cool so crystals form; filter and dry. Mark-scheme reward: evaporation/concentration, cooling, crystallisation — not “evaporate to dryness” unless anhydrous salt is required.
2. “Name the method used to separate sand from a mixture of sand and water. State what is collected as the filtrate.” Filtration; water is the filtrate (sand is residue). Reward: correct method and vocabulary.
3. “Explain why fractional distillation can separate a mixture of liquids.” Liquids have different boiling points; the fractionating column allows repeated evaporation and condensation so each fraction is collected at its boiling point. Reward: boiling point difference + column function.

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

How separation and purification connects to the rest of Experimental Techniques

Separation methods pair with Chromatography for analysing complex mixtures. After purification, Identification of Ions and Gases confirms the product. Organic work on Fuels assumes you understand fractional distillation of crude oil. 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

• Saying crystallisation evaporates the solid (you evaporate the solvent; crystals of solid remain).
• Confusing filtrate (liquid through filter) with residue (solid on paper).
• Using simple distillation when fractional distillation is needed for close-boiling liquids.
• Evaporating to dryness when the question asks for hydrated crystals (water of crystallisation is lost).
• Choosing filtration for a dissolved salt in water.

When you need more support

If separation questions keep costing marks — especially explain stems on fractional distillation — work through the Experimental Techniques topical past-paper questions and the Separation and Purification quiz, then get focused help from a Cambridge IGCSE Chemistry tutor.

Frequently asked questions

Is separation and purification hard in Cambridge IGCSE Chemistry? The methods are few and predictable. Marks are lost when students pick the wrong technique or confuse filtrate and residue.

When do I use fractional instead of simple distillation? When separating two or more miscible liquids with different boiling points, especially when those boiling points are close.

What is the difference between evaporation and crystallisation? Evaporation to dryness removes all solvent; crystallisation concentrates the solution then cools so orderly crystals form — better for hydrated salts.

How do I revise separation techniques effectively? Learn one example mixture per method, practise describe questions with labelled diagrams, then take the Separation and Purification quiz.

Ready to master Cambridge IGCSE Chemistry separation and purification?

Start with the Separation and Purification subtopic page, then book a free trial with a Cambridge IGCSE Chemistry specialist to turn separation techniques into guaranteed marks.

Ready to Excel in Your Studies?

Get personalised help from Tutopiya's expert tutors. Whether it's IGCSE, IB, A-Levels, or any other curriculum — we match you with the perfect tutor and your first session is free.

Book Your Free Trial