(Marking Scheme) A Level Edexcel Paper 3 General And Practical Principles In Chemistry

(MARKING SCHEME) A LEVEL EDEXCEL PAPER 3 GENERAL AND PRACTICAL PRINCIPLES IN CHEMISTRY General & Practical Principles in Chemistry • Original questions, worked reasoning and exam traps Paper context: Pearson's specification identifies Paper 3 (9CH0/03) as a 2 hour 30 minute, 120-mark paper. Questions may draw on Topics 1–19, including synoptic questions, calculations, extended responses and indirect assessment of practical skills. ■cite■turn0search24■turn0search0■ Important: This guide is independently written. It does not reproduce the 2024 paper, marking scheme, or the linked Stuvia document. It is designed to build the knowledge and reasoning skills needed for comparable questions. Edexcel A Level Chemistry Paper 3 • Original Premium Practice • 2026 Page 2 HOW TO APPROACH PAPER 3 1. Read the command word. Define, explain, calculate, determine, suggest, evaluate and compare require different answer styles. 2. Show working. In calculations, write the equation, substitute values, give units and sensible significant figures. 3. Link practical answers to errors. Do not write generic improvements; identify the source of uncertainty and how your change addresses it. 4. Think synoptically. A single question may combine equilibrium, energetics, kinetics, organic chemistry, analysis and practical reasoning. HIGH-YIELD PAPER 3 CHECKLIST Area What to remember Mass spectrometry m/z, ionisation, acceleration, flight time, isotopic abundance. Bonding shape, polarity, intermolecular forces, electronegativity. Energetics Hess cycles, bond enthalpy, entropy, Gibbs free energy. Kinetics rate equations, orders, k, activation energy, catalysts. Equilibrium Kc, Le Chatelier, temperature/pressure/concentration effects. Acids/bases Ka, pKa, buffers, titration curves, indicators. Redox oxidation/reduction, E°, cells, feasibility. Organic mechanisms, reagents, conditions, stereochemistry, polymers. Analysis IR, NMR, mass spectra, chromatography. Practical uncertainty, accuracy, precision, validity, reliability, evaluation. Edexcel A Level Chemistry Paper 3 • Original Premium Practice • 2026 Page 3 1. ATOMIC STRUCTURE & MASS SPECTROMETRY 1. Relative isotopic mass is defined relative to: A. 1/12 of the mass of a carbon-12 atom B. the mass of one proton C. the mass of one electron D. the mass of one mole of carbon ANSWER: A. 1/12 of the mass of a carbon-12 atom Rationale: Relative isotopic mass compares the mass of an isotope with one-twelfth of the mass of a carbon-12 atom. Exam trap / memory cue: Trap: Relative isotopic mass is dimensionless. 2. In a time-of-flight mass spectrometer, ions are separated primarily according to differences in: A. mass-to-charge ratio and resulting flight time B. boiling point C. electronegativity D. melting point ANSWER: A. mass-to-charge ratio and resulting flight time Rationale: For ions given comparable kinetic energy, lighter or more highly charged ions generally reach the detector sooner. Exam trap / memory cue: Memory cue: TOF = lighter m/z arrives first. 3. A sample contains 75% isotope X-35 and 25% isotope X-37. Its relative atomic mass is: A. 35.5 B. 36.0 C. 36.5 D. 37.0 ANSWER: A. 35.5 Rationale: (0.75 × 35) + (0.25 × 37) = 35.5. Exam trap / memory cue: Exam cue: weighted mean, not simpl