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Learn7405Paper 3 · Paper 3: Practical skills and synopticPractical skills and data analysisPractical techniques and data analysis
Practical skills and data analysis · Subtopic 1 of 2

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.

Cambridge 9701 Paper 3Edexcel YCH11 WCH13AQA 7405 Paper 3≈ 50 minRevision 1 · updated 2026-11-01
Section 1 of 14

Learning objectives

  • Carry out and record titrations correctly.
  • Calculate percentage uncertainties.
  • Calculate enthalpy changes from calorimetry data.
  • Recall key qualitative tests.
Pause and think

Why is a titre of 24.95 cm³ more precise than one of 5.00 cm³, even though both are read with the same burette?

Section 2 of 14

Core idea

Start hereResults you can trust

A titre that agrees to 0.10 cm³ and a temperature rise corrected for heat loss turn practical work into reliable data.

The big idea

Every measurement has an uncertainty. Good technique keeps it small, and calculations carry it through to the result.

Worked exampleCalorimetry

50.0 g of solution rises 6.5 °C; 0.0500 mol water formed. ΔH?

Goal
ΔH in kJ mol⁻¹.
Strategy
q = mcΔT, then ΔH = −q/n.
  1. q=50.0×4.18×6.5=1359 Jq=50.0\times4.18\times6.5=1359\ \text{J}
    Heat gained by solution.
  2. ΔH=−1.3590.0500=−27.2 kJ mol−1\Delta H=-\frac{1.359}{0.0500}=-27.2\ \text{kJ mol}^{-1}
    Exothermic, per mole.
Answer−27.2 kJ mol⁻¹.
✓ CheckTemperature rose, so negative ✓.
Percentage uncertainty of a titre
  1. ±0.05×2=±0.10 cm3\pm0.05\times2=\pm0.10\ \text{cm}^3
    Two burette readings.
  2. 0.1025.00×100=0.40%\frac{0.10}{25.00}\times100=0.40\%
    Relative to the titre.

Summary

  • Concordant titres within 0.10 cm³.
  • Double reading uncertainty for differences.
  • Extrapolate cooling curves.
Key words
Concordant
Results within 0.10 cm³ of each other.
Uncertainty
Range within which the true value probably lies.
HistoryGay-Lussac's burette. Joseph Louis Gay-Lussac designed an early burette around 1824; the word comes from French "burette", a small jug.
Fun factProfessional titrators. Quality-control labs use automatic titrators that add titrant in 0.001 cm³ steps and detect the end point with a pH electrode.
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