Which apparatus and techniques give reliable, accurate chemical data?
Common chemical apparatus and the laboratory techniques used to prepare, purify and analyse substances, including titration, distillation, reflux, vacuum filtration, recrystallisation, thin-layer chromatography, colorimetry and melting-point determination.
An SQA Advanced Higher Chemistry answer on common laboratory apparatus and techniques, covering the use of volumetric glassware, titration, distillation and reflux, vacuum filtration and recrystallisation, thin-layer chromatography, colorimetry and melting-point determination, and how each contributes to reliable and accurate data.
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What this key area is asking
The SQA wants you to know common chemical apparatus and the techniques used to prepare, purify and analyse substances, and to explain how each gives reliable, accurate data. Choosing the right apparatus, describing purification by recrystallisation and filtration, and using melting point and chromatography to check purity are reliable exam earners.
Measuring volumes accurately
A standard solution of accurately known concentration is prepared by weighing a solid on an accurate balance, dissolving it, and making up to the mark in a volumetric flask. These are far more accurate than a measuring cylinder, which is only used for approximate volumes.
Separating and purifying liquids
Distillation separates liquids by their different boiling points: the mixture is heated, the most volatile component vaporises first, and the vapour is cooled and collected in a condenser. Reflux heats a reaction mixture for a long time without losing volatile reactants or products, because the vapour continually condenses and runs back into the flask. Reflux is essential for slow organic reactions such as oxidations and esterifications.
Isolating and purifying solids
Analysing with chromatography and colorimetry
Thin-layer chromatography (TLC) separates the components of a mixture as a solvent rises up a coated plate; each component travels a characteristic distance, giving an value. TLC is used to monitor a reaction (watching the reactant spot fade and a product spot appear) and to check purity (a pure substance gives a single spot). Colorimetry measures the absorbance of a coloured solution; because absorbance is proportional to concentration, a calibration graph of absorbance against known concentrations lets the concentration of an unknown be read off.
Examples in context
These techniques are the practical foundation of the whole course. In an organic synthesis, a chemist refluxes the reactants, monitors progress by TLC, isolates the solid by vacuum filtration, purifies it by recrystallisation, and confirms purity by melting point, exactly the sequence used to make and check aspirin. In quantitative analysis, a standard solution made in a volumetric flask is delivered by pipette and titrated from a burette to find an unknown concentration, while colorimetry quantifies coloured transition metal ions such as copper(II) or manganese(VII). Choosing the most accurate apparatus, and justifying the choice, is precisely the skill the project and the question paper reward.
Try this
Q1. Name the apparatus used to deliver a fixed, accurately known volume of solution. [1 mark]
- Cue. A pipette.
Q2. State the purpose of recrystallisation. [1 mark]
- Cue. To purify a solid by dissolving it in hot solvent and crystallising it on cooling, leaving impurities in solution.
Q3. State what a sharp melting point at the literature value tells you about a solid. [1 mark]
- Cue. That the solid is pure.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA AH 20193 marksA student purifies an impure solid organic product. (a) Name the technique that uses a hot solvent to purify a solid by crystallisation. (b) Name the apparatus used to separate the purified crystals quickly from the solvent. (c) State how the melting point of the product confirms its purity.Show worked answer →
Markers reward the technique, the filtration apparatus and the purity check.
(a) The technique is recrystallisation: the solid is dissolved in the minimum volume of hot solvent, then cooled so pure crystals form while soluble impurities stay in solution.
(b) Vacuum (Buchner) filtration is used to separate the crystals quickly from the cold solvent, drawing the liquid through under reduced pressure.
(c) A pure compound has a sharp melting point close to the literature value. An impure sample melts over a wider range and at a lower temperature, so a sharp, correct melting point confirms purity.
SQA AH specimen2 marks(a) State why a pipette rather than a measuring cylinder is used to measure the aliquot in an accurate titration. (b) State the purpose of thin-layer chromatography in monitoring a reaction.Show worked answer →
The answer must link the pipette to accuracy and TLC to monitoring.
(a) A pipette delivers a fixed, accurately known volume with a much smaller uncertainty than a measuring cylinder, so the aliquot volume in the titration calculation is reliable. A measuring cylinder is too imprecise for accurate volumetric work.
(b) Thin-layer chromatography lets a chemist follow a reaction by comparing spots from the reaction mixture against the starting material; the disappearance of the reactant spot and the appearance of a product spot show how far the reaction has gone and whether it is complete.
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Sources & how we know this
- SQA Advanced Higher Chemistry Course Specification — SQA (2019)