This guide covers IGCSE Chemistry topic 2: experimental techniques. You will revise filtration, crystallisation, simple and fractional distillation, chromatography, and when to use each method.

Key concepts to revise

• Filtration – Separate insoluble solid from liquid; filter paper; residue and filtrate.
• Crystallisation – Separate soluble solid from solution; evaporate water; crystals form on cooling.
• Distillation – Separate liquid from solution (simple) or mixture of liquids (fractional); boil; condense; collect.
• Chromatography – Separate mixtures of coloured substances (e.g. inks, dyes); solvent moves up paper; different Rf values.

Exam tips and command words

• State – Which method to use for a given mixture (e.g. sand and water: filtration).
• Describe – The steps of filtration, crystallisation, or distillation; the setup for chromatography.
• Explain – Why fractional distillation separates liquids (different boiling points; column allows repeated condensation).
• Calculate – Rf value = distance moved by substance / distance moved by solvent.

Common mistakes

• Saying crystallisation “evaporates the solid” (you evaporate the solvent; the solid is left as crystals).
• Confusing filtrate (liquid that passes through) with residue (solid left on filter).
• Not stating that Rf is a ratio (no units); same substance same Rf in same solvent.

Revision checklist

• State which separation method to use for: insoluble solid + liquid; soluble solid + liquid; two liquids; coloured mixture.
• Describe the steps of filtration, crystallisation and simple distillation.
• Describe paper chromatography and how to calculate Rf.
• Explain why fractional distillation can separate liquids with different boiling points.

Next steps

Book a free trial with an IGCSE Chemistry tutor to practise separation and chromatography questions, or explore Tutopiya’s learning portal for more revision resources.