Practical Techniques: Experimental Design, Titrations, Chromatography and Separation

This guide covers Topic 12.1–12.4 — Experimental design, Acid–base titrations, Chromatography, and Separation and purification — for Cambridge IGCSE Chemistry 0620 and Cambridge O Level Chemistry 5070, 2026–2028 series. Topic 12.5, Identification of ions and gases, is covered separately in Identification of Ions and Gases.

Where this fits in 0620/5070

This is the “how do you actually do it” topic — it’s tested both directly (name the apparatus, describe the method) and indirectly, woven into questions from other topics. Salt preparation in Acids, Bases and Salts uses the filtration/crystallisation methods described here; a rate-of-reaction experiment in Rates of Reaction and Reversible Reactions depends on choosing the right apparatus from 12.1. Treat this topic as the toolkit the rest of the syllabus draws on, not an isolated block.

Syllabus coverage

CAMBRIDGE IGCSE CHEMISTRY 0620 / O LEVEL CHEMISTRY 5070

Core

• Naming appropriate apparatus for measuring time, temperature, mass and volume — stop-watches, thermometers, balances, burettes, volumetric pipettes, measuring cylinders, gas syringes (12.1)
• Suggesting advantages and disadvantages of experimental methods and apparatus (12.1)
• Defining solvent, solute, solution, saturated solution, residue and filtrate (12.1)
• Describing an acid–base titration, including the use of a burette, volumetric pipette and suitable indicator (12.2)
• Describing how to identify the end-point of a titration using an indicator (12.2)
• Describing how paper chromatography separates mixtures of soluble coloured substances, using a suitable solvent (12.3)
• Interpreting simple chromatograms to identify unknown substances by comparison, and to distinguish pure from impure substances (12.3)
• Describing and explaining separation/purification using a suitable solvent, filtration, crystallisation, simple distillation and fractional distillation (12.4)
• Suggesting suitable separation/purification techniques given information about the substances involved (12.4)
• Identifying substances and assessing purity using melting point and boiling point data (12.4)

Supplement / Extended (0620) · Required (5070)

• Describing how paper chromatography separates mixtures of soluble colourless substances, using a suitable solvent and a locating agent — specific locating agents are not required (12.3)
• Stating and using the Rf equation (12.3)

There is no Supplement content listed for 12.1, 12.2 or 12.4 — those three are Core-only, identical for every candidate regardless of tier. Both bullets above are Extended-only for 0620, but are required outcomes for every 5070 candidate — 5070 has no Core/Extended split, so an O Level candidate must know colourless-substance chromatography and the Rf equation regardless of the 0620-style tiering used elsewhere on this page.

Choosing apparatus (12.1)

Match the quantity to the apparatus — this is a very literal, name-the-tool skill:

Measuring	Apparatus
Time	Stop-watch
Temperature	Thermometer
Mass	Balance
A precise, variable volume of liquid added gradually	Burette
One exact, fixed volume of liquid	Volumetric pipette
An approximate volume of liquid	Measuring cylinder
Volume of a gas produced	Gas syringe

Key vocabulary you must be able to define exactly, not just recognise:

• Solvent — a substance that dissolves a solute
• Solute — a substance that is dissolved in a solvent
• Solution — a mixture of one or more solutes dissolved in a solvent
• Saturated solution — a solution containing the maximum concentration of solute dissolved in the solvent at a specified temperature
• Residue — a substance that remains after evaporation, distillation, filtration or a similar process
• Filtrate — a liquid or solution that has passed through a filter

Acid–base titrations (12.2)

A titration finds the exact volume of one solution needed to react completely with a known volume of another.

1. Measure a fixed volume of one solution (e.g. the alkali) into a conical
   flask using a volumetric pipette
2. Add a few drops of a suitable indicator
3. Fill a burette with the other solution (e.g. the acid)
4. Add the acid from the burette, swirling the flask, until the indicator
   just changes colour — this is the end-point
5. Read the volume of acid used from the burette

Identifying the end-point: the end-point is the exact point at which the indicator permanently changes colour with the addition of a single further drop — read as the volume at which the colour change first becomes permanent, not simply the first hint of a colour shift.

The salt-preparation route in Acids, Bases and Salts uses exactly this technique when the base is soluble (an alkali) — titrate first with an indicator to find the volume needed, then repeat without the indicator so the crystallised salt isn’t contaminated by it.

Chromatography (12.3)

Paper chromatography separates a mixture of soluble substances based on how strongly each one is attracted to the paper versus how soluble it is in the solvent — different substances travel different distances up the paper.

Coloured substances (Core): spot the mixture near the base of a strip of chromatography paper (above the level of the solvent), stand the paper in a suitable solvent, and let the solvent rise up the paper, carrying the different coloured components different distances depending on their solubility and attraction to the paper.

Colourless substances (0620 Extended/Supplement only; required for every 5070 candidate): the same method, but since there’s no colour to see directly, a locating agent is sprayed or applied afterwards to reveal the spots. You are not required to know any specific locating agent — only that one is needed for colourless substances.

Interpreting a chromatogram:

• Identifying unknowns — compare the position of an unknown spot against known reference substances run on the same chromatogram (same solvent, same paper, same conditions); a matching position (matching Rf) suggests the same substance.
• Pure vs impure — a pure substance produces exactly one spot; an impure substance separates into two or more spots.

Rf value (0620 Extended/Supplement only; required for every 5070 candidate):

Rf = distance travelled by substance / distance travelled by solvent

Both distances are measured from the same starting (baseline) point. Rf is always less than 1 (the substance never travels further than the solvent itself), and is used to identify a substance by comparing it against known Rf values measured under the same conditions.

Separation and purification (12.4)

Which method to use depends entirely on the properties of what you’re trying to separate:

Method	Separates	When to use
Using a suitable solvent	A soluble component from an insoluble one	One substance dissolves in the solvent, the other doesn’t
Filtration	An insoluble solid from a liquid	You want the residue, the filtrate, or both
Crystallisation	A dissolved solid from its solvent	The solid is much more soluble hot than cold, or you want to recover a solute as pure crystals
Simple distillation	A solvent from a dissolved solute	You want the liquid (solvent) back, e.g. pure water from salt solution
Fractional distillation	Two or more miscible liquids	The liquids have different, known boiling points (e.g. separating ethanol from water)

Assessing purity from melting/boiling point: a pure substance melts and boils at a single, sharp, exact temperature (its known melting/boiling point). An impure substance melts over a range of temperatures, starting below and often finishing below the pure substance’s true melting point — and boils over a range as well, generally above the pure substance’s true boiling point. Comparing a measured melting or boiling point (and whether it’s a sharp point or a range) against the known value for the expected pure substance is a direct purity test.

Common mistakes

• Reading a burette from the wrong reference point, or misreading the meniscus — always read at eye level, from the bottom of the meniscus.
• Adding the indicator before deciding the correct titration volume for salt preparation, then crystallising with the indicator still present — this contaminates the crystals; the indicator run is only to find the volume, then it’s repeated without the indicator.
• Confusing simple distillation with fractional distillation. Simple distillation separates a dissolved solid or one liquid from a mixture where only one component is volatile; fractional distillation is specifically for separating two or more miscible liquids with different boiling points.
• Forgetting that a pure substance melts/boils at a sharp, exact point — stating only “impure substances have a different melting point” without the key idea that impurity produces a range, not just a shifted single value.
• Applying Rf backwards — the formula is always distance travelled by the substance over distance travelled by the solvent, never the other way round.

Quick revision checklist

• Matching each quantity (time, temperature, mass, volume) to its correct apparatus
• Definitions: solvent, solute, solution, saturated solution, residue, filtrate
• The exact titration method and how to identify the end-point
• Coloured vs colourless chromatography (0620 Extended, 5070 required, for the colourless case), and how to interpret a chromatogram for identity and purity
• (0620 Extended, 5070 required) the Rf equation and how to apply it
• The five separation/purification methods and when each applies
• Using melting point/boiling point (sharp point vs range) to assess purity

Related resources

• Acids, Bases and Salts — uses titration and the excess/filter/crystallise route directly
• Identification of Ions and Gases — Topic 12.5, the qualitative-analysis half of this topic
• Rates of Reaction and Reversible Reactions — practical methods for investigating rate rely on the apparatus covered here
• Cambridge IGCSE Chemistry hub · Cambridge O Level Chemistry hub

Written against Cambridge IGCSE Chemistry 0620 and Cambridge O Level Chemistry 5070, 2026–2028 series. Always check the current syllabus for your examination year.