How to Study Experimental Techniques for IGCSE Chemistry

Experimental techniques is the first topic in the 0620 syllabus, and students sometimes treat it as a simple introductory chapter not worth serious study. This is a mistake. The techniques covered here — separation methods, measurement, and practical reasoning — are tested on every paper. Paper 6 (Alternative to Practical) is built almost entirely on this content. Papers 2 and 4 regularly ask about apparatus, procedure, and experimental design. Studying this topic thoroughly gives you marks across the entire exam.

The separation techniques

For each technique, you need four pieces of knowledge:

1. What it separates: The type of mixture (solid from liquid, miscible liquids, etc.)
2. What property difference it exploits: Boiling point, solubility, particle size, etc.
3. The apparatus and procedure: What equipment is used and in what order
4. When to choose it: Given a mixture, which technique is appropriate

Filtration

Separates an insoluble solid from a liquid. Uses filter paper in a funnel. The liquid passes through (filtrate); the solid stays on the paper (residue). Choose this when you have an insoluble solid in a liquid, like sand in water, or excess base after a neutralisation reaction in salt preparation.

Evaporation and crystallisation

Separates a dissolved solid from its solution. Evaporation removes the solvent by heating. Crystallisation is controlled evaporation: heat until the point of crystallisation (when crystals start forming at the edge), then allow to cool slowly for larger, purer crystals. The distinction matters — the exam penalises writing “evaporate to dryness” when crystallisation is needed, because rapid evaporation produces poor crystals with trapped impurities.

Simple distillation

Separates a liquid from a dissolved solid, or collects a pure solvent from a solution. The solution is heated, the solvent evaporates, passes through a condenser (cooled by running water), and is collected as a pure liquid. Choose this when you want the liquid, not the solid (if you wanted the solid, you would use evaporation).

Fractional distillation

Separates two or more miscible liquids with different boiling points. The fractionating column provides a temperature gradient: the liquid with the lowest boiling point reaches the top first and passes into the condenser. The thermometer reading tells you which liquid is being collected. Choose this for mixtures like ethanol and water.

Paper chromatography

Separates dissolved substances based on their relative solubility in the solvent (mobile phase) versus their attraction to the paper (stationary phase). More soluble substances travel further up the paper. A baseline is drawn in pencil (not ink, which would dissolve), spots of the mixtures are placed on the line, and the paper is dipped into the solvent (which must be below the baseline).

Rf value (extended) = distance moved by substance / distance moved by solvent front. This value is constant for a given substance under the same conditions and can be used to identify unknown substances by comparison.

Separating funnel

Separates two immiscible liquids (like oil and water). The denser liquid settles at the bottom and is drained off through the tap.

Measurement and accuracy

Reading scales

Read the meniscus at eye level for liquids. The bottom of the meniscus is the correct reading for most liquids. For a burette, readings are taken from the top (zero is at the top).

Appropriate apparatus

The exam may ask you to choose the right apparatus for a measurement:

• Measuring cylinder: for approximate volumes (accuracy to 1 cm3 or 0.5 cm3)
• Burette: for precise volumes in titrations (accuracy to 0.05 cm3)
• Pipette: for fixed accurate volumes (25.0 cm3)
• Balance: for mass measurements (accuracy depends on the balance, typically 0.01 g)
• Thermometer: for temperature (accuracy to 0.5 or 1 degree C)

Choosing a beaker to measure 25 cm3 when a measuring cylinder is available is a common error. The exam awards marks for selecting the most appropriate piece of apparatus for the required precision.

Practical reasoning skills

These skills appear on every Paper 6 and frequently on Paper 4:

Sources of error

Identify what could make the results inaccurate. Common sources:

• Heat loss to surroundings in calorimetry experiments
• Incomplete reactions (not all the reactant reacted)
• Spillage or transfer losses
• Parallax error when reading scales
• Impure reagents

Improvements

Suggest how to reduce errors. Match each improvement to a specific error:

• Use a lid or insulation to reduce heat loss
• Use excess reactant to ensure complete reaction
• Repeat the experiment and take an average to improve reliability
• Use a more precise measuring instrument

Variables

Identify the independent variable (what you change), dependent variable (what you measure), and control variables (what you keep the same). This framework applies to every experiment in the syllabus.

Study approach

Drawing apparatus

You need to be able to draw and label apparatus setups for:

• Filtration
• Simple distillation
• Fractional distillation
• Chromatography
• Gas collection (over water, using a gas syringe)
• Electrolysis cells
• Titration

Practise drawing each setup from memory. Use our diagram guide for the conventions examiners expect: correct proportions, standard labels, heat arrows under the apparatus (not flames wrapping around the beaker).

Linking to other topics

Separation techniques are not isolated. They appear throughout the syllabus:

• Salt preparation uses filtration, evaporation, and crystallisation
• Identifying substances uses chromatography
• Collecting gases uses displacement of water or a gas syringe
• Water purification uses distillation and filtration

When studying other topics, note which experimental techniques are involved. This builds the cross-topic understanding that Paper 6 and extended response questions test.

Past paper practice

Paper 6 is the primary exam for this topic. Work through past Paper 6 sessions under timed conditions, marking against the scheme. The Paper 6 guide covers the specific question types and how to approach them. Paper 4 structured questions also draw on practical reasoning, particularly “describe an experiment to show…” questions.