Measurements & Experimental Techniques
Chemistry experimental techniques hub: measurement, gas collection, purity, and separation. Includes Paper 3 skill lessons, exam traps, and quizzes.
Before you begin
Accurate measurement and sound technique are the foundation of chemistry. This is the first topic: the lessons cover measuring and recording, planning and evaluating an investigation, then titration, collecting gases, testing purity and separating mixtures.
Learning goals
- name appropriate apparatus for the measurement of time, temperature, mass and volume; including burettes, pipettes, measuring cylinders and gas syringes
- suggest suitable apparatus, given relevant information, for a variety of simple experiments, including drying and collection of gases and measurement of rates of reaction (drying agents will be limited to calcium oxide, concentrated sulfuric acid and fused calcium chloride).
- describe methods of separation and purification for the components of mixtures, to include: — use of a suitable solvent, filtration and crystallisation or evaporation
- describe methods of separation and purification for the components of mixtures, to include: — sublimation
- describe methods of separation and purification for the components of mixtures, to include: — distillation and fractional distillation (see also 11.1(b))
- describe methods of separation and purification for the components of mixtures, to include: — use of a separating funnel
- describe methods of separation and purification for the components of mixtures, to include: — paper chromatography
- suggest suitable separation and purification methods, given information about the substances involved in the following types of mixtures: — solid-solid
- suggest suitable separation and purification methods, given information about the substances involved in the following types of mixtures: — solid-liquid
- suggest suitable separation and purification methods, given information about the substances involved in the following types of mixtures: — liquid-liquid (miscible and immiscible)
- interpret paper chromatograms including comparison with ‘known’ samples and the use of Rf values
- explain the need to use locating agents in the chromatography of colourless compounds (knowledge of specific locating agents is not required)
- deduce from given melting point and boiling point data the identities of substances and their purity.
- explain the importance of measuring the purity in substances used in everyday life, e.g. foodstuffs and drugs.
- follow a sequence of instructions;
- use techniques, apparatus and materials;
- make and record observations, measurements and estimates;
- interpret and evaluate observations and experimental results;
- plan investigations, select techniques, apparatus and materials;
- evaluate methods and suggest possible improvements.
Syllabus statements covered
- name appropriate apparatus for the measurement of time, temperature, mass and volume; including burettes, pipettes, measuring cylinders and gas syringes
- suggest suitable apparatus, given relevant information, for a variety of simple experiments, including drying and collection of gases and measurement of rates of reaction (drying agents will be limited to calcium oxide, concentrated sulfuric acid and fused calcium chloride).
- describe methods of separation and purification for the components of mixtures, to include: — use of a suitable solvent, filtration and crystallisation or evaporation
- describe methods of separation and purification for the components of mixtures, to include: — sublimation
- describe methods of separation and purification for the components of mixtures, to include: — distillation and fractional distillation (see also 11.1(b))
- describe methods of separation and purification for the components of mixtures, to include: — use of a separating funnel
- describe methods of separation and purification for the components of mixtures, to include: — paper chromatography
- suggest suitable separation and purification methods, given information about the substances involved in the following types of mixtures: — solid-solid
- suggest suitable separation and purification methods, given information about the substances involved in the following types of mixtures: — solid-liquid
- suggest suitable separation and purification methods, given information about the substances involved in the following types of mixtures: — liquid-liquid (miscible and immiscible)
- interpret paper chromatograms including comparison with ‘known’ samples and the use of Rf values
- explain the need to use locating agents in the chromatography of colourless compounds (knowledge of specific locating agents is not required)
- deduce from given melting point and boiling point data the identities of substances and their purity
- explain the importance of measuring the purity in substances used in everyday life, e.g. foodstuffs and drugs.
- follow a sequence of instructions
- use techniques, apparatus and materials
- make and record observations, measurements and estimates
- interpret and evaluate observations and experimental results
- plan investigations, select techniques, apparatus and materials
- evaluate methods and suggest possible improvements.
Lessons
Work through them in order.
Measurement and recording
Planning and evaluation
- Planning a chemistry investigationPlan fair, safe and repeatable practical work.
- Presenting practical results in tables and graphsPresent measurements in tables and graphs, and interpret the patterns.
- Evaluating practical results and improving a methodEvaluate limitations and propose specific improvements.
Collection and separation
- Titration technique and concordant resultsCarry out accurate titrations and select concordant titres.
- Collecting gases and measuring their volumesChoose how to collect a gas from its solubility and density, and measure its volume.
- Choosing a drying agent for a gasRemove water vapour without removing the gas: compare calcium oxide, concentrated sulfuric acid and fused calcium chloride.
- Choosing separation methodsUse physical properties to select methods, recover solids and separate immiscible liquids.
- Simple and fractional distillationRecover a solvent or separate miscible liquids by vaporisation, condensation and repeated enrichment in a fractionating column.
- Paper chromatography and Rf valuesSet up paper chromatography, compare unknown and reference spots, calculate Rf and explain the limits of the evidence.
- Using evidence to assess purityJudge purity from melting and boiling points and from chromatography.
Practise and check
Recommended nextExperimental Chemistry topic check
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Topic reference
Quick Reference
| Item | Quick rule / reminder |
|---|---|
| Volume conversions | 1 cm³ = 1 mL and 1 dm³ = 1 L = 1000 cm³ |
| Meniscus reading | Read at eye level; use the bottom of a concave meniscus (most aqueous solutions) and the top of a convex meniscus |
| Purity clue | At the same pressure, a pure substance has a sharp melting or boiling point; an impure sample usually changes over a range |
| Gas collection choice | Need a measured volume → gas syringe; otherwise, an insoluble gas can be collected over water, while a soluble gas is collected by displacement of air using its density |
| Paper chromatography | R_f = (distance from start line to centre of spot)/(distance from start line to solvent front) (no units; 0–1) |
| Chromatography setup | Start line in pencil; solvent level below the start line |
| Separating funnel | Remove the stopper before opening the tap; drain the lower layer first |
Core knowledge to remember
- Accuracy: how close a reading is to the true value.
- Precision: how close repeated readings are to each other.
- Resolution: the smallest change that an instrument can display or that can be read from its scale.
- Parallax error: reading a scale from the wrong eye position.
- Residue: insoluble solid left on the filter paper.
- Filtrate: liquid that passes through the filter paper.
- Distillate: liquid collected during distillation.
- Pure substance: melts/boils at a fixed temperature (sharp point).
- Random error: unpredictable variation; repeats reduce it.
For Paper 3 revision, use the K324 / 6092 Chemistry Practical hub.
Common mistakes
- Meniscus + parallax: measuring cylinders must be read at eye level.
- Gas collection method: avoid water displacement for soluble gases.
- Residue vs filtrate: residue stays on the paper; filtrate passes through.
- Purity logic: mixtures melt/boil over a range, not a point.
- Chromatography setup: start line in pencil; solvent level below the start line.
- R_f mistakes: R_f has no units, is between 0 and 1, and is measured from the start line.
- Separating funnel flow: remove the stopper before opening the tap; drain the lower layer first.
- Apparatus choice: match the apparatus to the task; a gas syringe measures gas volume, while a measuring cylinder is less precise for liquid volume.