How is an experimental investigation planned, analysed and reported?
The practical skills of scientific inquiry assessed by the project: planning a valid investigation, generating reliable raw data, processing and presenting results, analysing data with uncertainties, evaluating the procedure, and reporting with referencing.
An SQA Advanced Higher Chemistry answer on the practical skills assessed by the project, covering planning a valid investigation, generating reliable raw data, processing and presenting results, analysing data including accuracy, precision and uncertainty, evaluating the procedure, and writing a structured report with references.
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What this key area is asking
The SQA wants you to demonstrate the practical skills assessed by the project: planning a valid investigation, generating reliable raw data, processing and presenting results, analysing data with uncertainties, evaluating the procedure, and reporting with references. Distinguishing accuracy from precision, identifying random and systematic errors, and structuring a report are reliable exam earners.
Planning a valid investigation
Good planning also selects the most appropriate apparatus (the most accurate available for the measurement) and chooses a method that produces reliable, replicable data with enough repeats.
Generating reliable raw data
Raw data must be recorded as it is measured, with units and to a number of significant figures that matches the precision of the apparatus. Measurements should be repeated so that a mean can be taken; a single reading cannot be checked for reliability. Outliers (anomalous results) should be identified and, where justified, excluded from the mean.
Processing and presenting results
Processing turns raw data into a result: calculating a mean, a rate, a concentration, a percentage yield or an atom economy. Results are presented in clearly headed tables (with units in the headings), and trends are shown with line graphs or calibration curves, drawn with labelled axes, a sensible scale and a best-fit line. A calibration graph, for example of colorimeter absorbance against known concentrations, lets an unknown be read off.
Analysing: accuracy, precision and uncertainty
Evaluating and reporting
Evaluation judges the reliability (would repeats give the same result?) and validity (did the experiment measure what it set out to?) of the procedure, identifies the main sources of error, and suggests realistic improvements. The report is structured: aim, underlying chemistry, method, results, analysis, evaluation and conclusion. All sources of information must be referenced to acknowledge other work, allow the reader to check it, and avoid plagiarism.
Examples in context
These skills are assessed in the project but also sampled in the question paper. A candidate investigating the rate of a reaction plans to change one concentration at a time, controls the temperature, records times with units, repeats each run, plots a graph, and concludes the order of reaction, while evaluating the timing uncertainty. A candidate measuring the concentration of a coloured ion builds a colorimeter calibration curve, reads off the unknown, and discusses the accuracy of the colorimeter. The distinction between random and systematic error explains why some experiments need more repeats and others need recalibration, and the requirement to reference sources mirrors the standard expected in first-year university laboratory reports, which is exactly what the Advanced Higher project prepares candidates for.
Try this
Q1. State the difference between accuracy and precision. [2 marks]
- Cue. Accuracy is closeness to the true value; precision is closeness of repeated measurements to each other.
Q2. State how taking the mean of several repeats improves a result. [1 mark]
- Cue. It reduces the effect of random errors, because scatter above and below the true value tends to cancel.
Q3. State why sources of information must be referenced in the project report. [1 mark]
- Cue. To acknowledge other people's work, allow it to be checked, and avoid plagiarism.
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 measures a reaction rate three times and obtains values that agree closely but are all higher than the true value. (a) State whether the results are precise, accurate, or both. (b) Suggest one possible cause. (c) State how repeating measurements improves the reliability of a mean value.Show worked answer →
Markers reward distinguishing precision from accuracy, a systematic-error cause, and the role of repeats.
(a) The results are precise (they agree closely with each other) but not accurate (they are consistently away from the true value).
(b) A consistent offset suggests a systematic error, such as an uncalibrated instrument or a consistent timing delay, which shifts every reading the same way.
(c) Repeating measurements and taking the mean reduces the effect of random errors, because random scatter above and below the true value tends to cancel, making the mean more reliable.
SQA AH specimen2 marksIn the project report, (a) state why raw data should be recorded with units and to an appropriate number of significant figures, and (b) state why sources of information must be referenced.Show worked answer →
The answer must link data recording to validity and referencing to academic honesty.
(a) Recording raw data with units and to an appropriate number of significant figures reflects the precision of the apparatus and lets the reader judge the reliability of the results; missing units or false precision make the data unusable.
(b) Sources must be referenced to acknowledge other people's work, to allow the reader to check the underpinning chemistry, and to avoid plagiarism. Referencing is a requirement of the project and of good scientific practice.
Related dot points
- 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.
- Stoichiometric calculations from balanced equations, gravimetric analysis from measured masses, volumetric analysis including acid-base, redox, complexometric and back titrations, and the calculation of percentage yield and atom economy.
An SQA Advanced Higher Chemistry answer on stoichiometric calculations, covering the mole and balanced equations, gravimetric analysis from measured masses, volumetric analysis through acid-base, redox, complexometric and back titrations, and the calculation of percentage yield and atom economy from experimental data.
- The reactions of the main functional groups including nucleophilic substitution, elimination, oxidation, reduction, condensation and hydrolysis, the use of these reactions to design multi-step synthetic routes, and the assessment of a route by percentage yield, atom economy and hazards.
An SQA Advanced Higher Chemistry answer on synthesis, covering the reactions of the main functional groups (nucleophilic substitution, elimination, oxidation, reduction, condensation and hydrolysis), how these reactions are combined into multi-step synthetic routes, and how a route is assessed by percentage yield, atom economy and hazards.
- Rate equations of the form rate = k[A]^m[B]^n, the order of reaction with respect to each reactant and overall, the rate constant and its units, and the link between the rate equation, the rate-determining step and a reaction mechanism.
An SQA Advanced Higher Chemistry answer on kinetics, covering rate equations of the form rate = k[A]^m[B]^n, finding the order of reaction with respect to each reactant and overall, calculating the rate constant and its units, and using the rate equation to identify the rate-determining step and propose a reaction mechanism.
Sources & how we know this
- SQA Advanced Higher Chemistry Course Specification — SQA (2019)