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LearnAQA7405First teaching 2015Paper 3 · Paper 3: Practical skills and synopticPractical skills and data analysis
Paper 3 · Module

Practical skills and data analysis

2 subtopics≈ 95 min in total
Start the module: Practical techniques and data analysisOpen graphing calculator

  1. Practical techniques and data analysis

    Titration: rinse the burette with the solution, fill, remove the funnel, read the bottom of the meniscus at eye level to ±0.05 cm³; do a rough titre, then accurate titres until two are concordant (within 0.10 cm³); average only concordant titres. Uncertainty: each reading has an uncertainty; a burette titre uses two readings (±0.10 cm³). % uncertainty=uncertaintyvalue×100\%\,\text{uncertainty}=\frac{\text{uncertainty}}{\text{value}}\times100; add % uncertainties when quantities are multiplied or divided. Calorimetry: q=mcΔTq=mc\Delta T; ΔH=−q/n\Delta H=-q/n. Extrapolate a cooling curve to correct for heat loss. Qualitative tests: precipitates with NaOH/NH₃, gas tests, flame tests, organic functional group tests.

    ≈ 50 min

  2. Planning and evaluating experiments

    Planning: state the independent (changed), dependent (measured) and controlled variables; write a hypothesis; choose apparatus and quantities (with reasons); give a step-by-step method; identify hazards and precautions. Analysis: tabulate with units; plot graphs with the independent variable on xx; draw a line of best fit; calculate gradients using a large triangle; use derived quantities (1/t, ln k). Evaluation: identify anomalies; distinguish random errors (scatter; reduce by repeats) from systematic errors (shift all results; reduce by changing method); calculate % error against a reference value and compare with total % uncertainty; suggest specific improvements.

    ≈ 45 min