Chemistry › Working in the laboratory
Working in the laboratory
Unit C00 · 3 lessons.
Reading a burette to the nearest 0.05 cm³, stating the uncertainty in a reading and carrying it into a percentage, choosing the right glassware, and writing a formula, an ionic equation and its state symbols without hesitating: every later unit assumes these. None of it is a topic you finish. It is the working language of the required practicals and of every calculation that follows.
Most marks here go in the uncertainty arithmetic. A titre is the difference of two burette readings, each ±0.05 cm³, so the titre itself is ±0.10 cm³, not ±0.05 cm³. An answer quoted to more significant figures than the least precise measurement claims a precision the apparatus never had.
On the written papers it is set on AQA Papers 1, 2 and 3, OCR A Papers 1, 2 and 3, Edexcel Papers 1, 2 and 3 and Cambridge Papers 1 and 2.
Specification sections: AQA 3.1.2.5 · OCR A 1.1.3, 1.1.4, 2.1.2, 2.1.4 · Edexcel 5.6 to 5.16, 18.21, 3.10 · CAIE 2.3
Notes
Illustrated notes for each topic in this unit, with worked examples and a checklist of objectives.
- Measurement, uncertainty and significant figures in chemistry
Resolution and the uncertainty of a single reading on a burette, pipette, volumetric flask, balance and thermometer, doubling the uncertainty for a difference of two readings, percentage uncertainty and how it combines through a calculation, reducing percentage uncertainty by measuring more, significant figures, accuracy and precision, random and systematic error, parallax, concordant and anomalous titres in a mean, and the maths a chemistry calculation uses: standard form, rearranging, unit conversion, logarithms, and the gradient and intercept of a straight-line graph.
- Apparatus, techniques and safety: the twelve required practicals in outline
The pipette, burette, volumetric flask and measuring cylinder and when to use each, weighing by difference, the water bath, heating under reflux, simple distillation, filtration under gravity and under reduced pressure, recrystallisation and melting point, hazard and risk, hazard pictograms and the fume cupboard, the hazards of concentrated acids, bromine, sodium and organic solvents, and a map of the twelve AQA required practicals.
- Formulae, equations and state symbols
Formulae of ionic compounds from the charges on common ions, including polyatomic ions and brackets, the diatomic elements, balancing equations by inspection, the four state symbols and the meaning of (aq), the solubility rules for deciding what precipitates, state symbols from observations, hydrated salts and water of crystallisation, ionic equations and spectator ions, the formulae of common acids, alkalis and their salts, ionic equations for acids with carbonates, and half-equations as a preview of redox.
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