Calculations
Quantitative chemistry skills: mole relations, concentrations, yields, and equation-based numerical reasoning.
This route helps when you keep missing the same type of question across different topics. Use it to combine lesson notes with linked practice and tools in one place.
Notes and Hubs in This Route
- Assigning and Calculating Oxidation States
Calculate oxidation states in elements, ions and compounds, then use increases and decreases to identify oxidation and reduction in K324 / 6092 redox reactions.
- Relative atomic, molecular and formula mass
Ar and Mr (formula mass): understand the carbon-12 comparison and calculate relative masses accurately using subscripts and brackets.
- Atomic structure and particle counts
Describe the nucleus and electron shells, compare subatomic particles, and count protons, neutrons and electrons in atoms and single-atom ions.
- Electron configuration
Arrange electrons in shells for the first 20 elements, identify valence electrons and use neutral-atom arrangements to find group and period.
- Finding empirical and molecular formulae
Empirical and molecular formula: find simplest whole-number ratios from mass/% data, then use Mr to get the molecular formula.
- Writing and balancing chemical equations
Chemical equations: write reactants → products, balance using coefficients, and add state symbols (s/l/g/aq) without changing subscripts.
- Writing chemical symbols and formulae
Read chemical notation, balance ion charges and use brackets correctly. Distinguish simplest atom ratios from the actual atoms in a molecule.
- Limiting reactants and excess left over
Limiting reactant: identify what runs out first using moles and the balanced equation, then calculate theoretical yield and excess left.
- Gas volumes and reacting amounts
Convert gas volumes into moles at room temperature and pressure, then use a balanced equation to calculate reacting masses and gas volumes.
- Moles, molar mass and particle counts
Use the mole to connect mass and particle counts. Choose the correct entity and molar mass, keep units consistent and round the final answer.
- Percentage composition by mass
Percentage composition by mass: calculate the element contribution, divide by the compound's total relative mass, then multiply by 100.
- Percentage purity: finding the pure part
Find the pure substance in an impure sample from gas or titration data, calculate percentage purity, and combine purity with percentage yield.
- Percentage yield: actual versus theoretical
Calculate percentage yield from actual and theoretical amounts, distinguish it from purity, and explain low or apparently excessive experimental yields.
- Solution concentration and titration calculations
Use mass and molar concentration, conserve solute amount during dilution, and calculate an unknown concentration from a titration and its balanced equation.
- Stoichiometry & The Mole Concept
Chemistry stoichiometry hub: formulas, balanced equations, mole calculations, concentration, limiting reagent, and yield/purity. Practise the topic with its check.
- Speed of Reaction
Rate of reaction: define change per unit time, choose a measurable quantity, calculate rates with units and interpret reaction graphs.
- Atomic Orbitals: Energies and Shapes (A Level)
Describe the number, relative energies, and shapes of s, p and d orbitals (n=1–3) plus 4s and 4p, and use them to support electron configuration answers.
- Atomic Structure (A Level)
A Level atomic structure notes: nuclides and ions, orbitals and electron configurations, and first/successive ionisation energies (trends, anomalies, data).
- Dalton’s Law and Partial Pressures (A Level)
Use Dalton’s Law to calculate partial pressures from mole fractions and total pressure, and apply it to gas collections over water.
- First Ionisation Energy Trends (A Level)
Define first ionisation energy and explain periodic trends using nuclear charge, shielding, and distance from the nucleus.
- The Gaseous State (A Level)
A Level gaseous state notes: pV = nRT calculations, Dalton’s law and partial pressures (including gas over water), and real-gas deviations with unit traps.
- Ideal Gas Model and pV = nRT (A Level)
Use the ideal gas model and pV = nRT with correct units, and solve for moles, molar mass, or gas volume in data questions.
- Orbitals and Electron Configuration (A Level)
Use orbitals (s/p/d) to write electron configurations for atoms and ions, including the 4s-before-3d removal rule for transition-metal cations.
- Real Gases and Deviations (A Level)
Explain when gases deviate from ideal behaviour and link deviations to intermolecular forces and molecular size at very high pressure and very low temperature.
- Subatomic Particles, Isotopes, Ions (A Level)
Use proton/neutron/electron facts to interpret nuclide symbols, explain isotopes and ions, and predict deflection of beams in electric fields.
- Successive Ionisation Energies (A Level)
Interpret successive ionisation energy data to deduce valence electrons and group, and explain large jumps using shell changes.
- Electrolysis Predictions and Faraday’s Law (A Level)
Predict molten and aqueous electrolysis products, write balanced half-equations, and calculate charge, electron amount, mass or gas volume using Faraday’s law.
- Reaction Kinetics (A Level)
A Level reaction kinetics notes: rate laws and orders, initial rates, concentration–time graphs and half-life, mechanisms/RDS, and catalysis.
- Titration Curves and Indicators (A Level)
Interpret acid–base titration curves, identify buffer regions and equivalence points, and choose suitable indicators with clear justification.
- Chemistry of Aqueous Solutions (A Level)
A Level aqueous equilibria notes: pH and Ka/Kb/Kw calculations, buffers and titration curves, Ksp and precipitation, plus common ion effect and complex ions.
- Bond Enthalpy Calculations (A Level)
Estimate reaction enthalpy using average bond enthalpies (ΔH ≈ Σ bonds broken − Σ bonds formed), with sign conventions and exam pitfalls.
- Buffer Solutions (A Level)
Understand buffer action and calculate pH changes using Ka/pKa and concentration ratios, including approximation checks and common exam traps.
- Calorimetry (q = mcΔT) (A Level)
Perform calorimetry calculations using q = mcΔT, then convert to ΔH per mole with correct signs, units, and heat-loss corrections.
- Cell Potentials and Spontaneity (A Level)
Calculate E°cell, predict electron flow direction, and connect the sign of E°cell to feasibility under standard conditions.
- Chemical Equilibria (A Level)
A Level chemical equilibria notes: dynamic equilibrium and Le Chatelier, Kc/Kp expressions, ICE-table calculations, equilibrium composition, and Haber process.
- Common Ion Effect and Complex Ions (A Level)
Predict solubility changes using the common ion effect, and explain how complex-ion formation increases solubility in linked equilibria.
- Complex Ions, Ligands, Ligand Exchange (A Level)
Define ligands and complexes, then explain the prescribed copper(II) water, ammonia and chloride exchanges and oxygen/carbon monoxide exchange in haemoglobin.
- Concentration–Time Graphs and Half-life (A Level)
Recognise 0th and 1st order behaviour from concentration–time and rate plots, use half-life to test reaction order, and extract k correctly.
- d-Orbital Splitting and Colour (A Level)
Use octahedral d-orbital orientation, splitting and d–d transitions to explain why many transition-metal complexes are coloured.
- ΔG = −nFE (A Level)
Link electrode potentials to energetics using ΔG° = −nFE°cell, and connect feasibility, electron count, and cell voltage in one chain.
- Empirical and Molecular Formula (A Level)
Use the exam-proof workflow to find empirical and molecular formulae from composition data, including hydrates and combustion-style traps.
- Energetics & Thermodynamics (A Level)
A Level energetics and thermodynamics notes: calorimetry, Hess and Born–Haber cycles, lattice energy, entropy, and Gibbs free energy (ΔG) reasoning.
- Enthalpy Changes and Energy Profiles (A Level)
Use energy profile diagrams to interpret ΔH and activation energy, and write correct exothermic/endothermic explanations.
- Entropy and Gibbs Free Energy (A Level)
Predict entropy change and use ΔG° = ΔH° − TΔS° to decide feasibility, with careful signs, units, and data-booklet cues.
- Equilibrium Composition Calculations (A Level)
Solve Kc/Kp equilibrium composition questions with ICE tables, justified approximations, and quick sanity checks that prevent errors.
- Equilibrium Constants (Kc and Kp) (A Level)
Write correct Kc and Kp expressions, interpret what magnitude means, and avoid the common expression, units and pressure traps.
- Gas Calculations (pV = nRT) (A Level)
Use pV = nRT safely: consistent units, correct R, Pa/kPa and cm³↔dm³ conversions, and gas stoichiometry traps that lose marks.
- Hess’ Law and Cycles (A Level)
Use Hess’ law to build enthalpy cycles and calculate unknown ΔH values from formation/combustion data, with clean sign/multiple handling.
- Initial Rates Method (A Level)
Deduce reaction orders from initial-rate data and build the rate equation using comparisons, including the common table-reading and rounding traps.
- Ka, Kb, Kw, pKa, pKb (A Level)
Define Ka, Kb, Kw, pKa and pKb, and use key relationships to move between constants, pH and equilibrium reasoning with exam-safe meanings.
- Ksp and Solubility Calculations (A Level)
Write Ksp expressions, calculate molar solubility, and predict precipitation using Qsp vs Ksp, with a repeatable exam workflow.
- Lattice Energy and Born–Haber Cycles (A Level)
Define lattice energy, predict trends with ionic charge/radius, and use Born–Haber cycles to connect lattice energy to formation enthalpy.
- Mechanisms and Rate-determining Step (A Level)
Link mechanisms to rate equations using the slow step (RDS), and perform the ‘consistency check’ between mechanism and observed rate law.
- Mole and Avogadro Constant (A Level)
Learn the mole as a counting unit: Avogadro constant (NA), particles vs moles, and the core equations you reuse everywhere.
- pH Calculations (Strong and Weak) (A Level)
Calculate pH for strong and weak acids/bases using Ka/Kb, with clear approximations, ICE tables when needed, and final-answer checks.
- Rate Equations, Orders, Rate Constant (A Level)
Use rate equations to connect rate to concentration, deduce orders, and handle rate constant k units with methodical comparisons and checks.
- Reacting Masses and Limiting Reagent (A Level)
Solve reacting-mass questions reliably: find the limiting reagent, calculate theoretical yield, handle leftovers, and avoid ratio-table mistakes.
- Solution Concentration and Dilution (A Level)
Use c = n/V and c1V1 = c2V2 safely with correct units (dm³ vs cm³), and avoid the most common dilution and mixing mistakes.
- Standard Electrode Potentials and the SHE (A Level)
Define standard electrode potential (E°), understand standard conditions, and use the standard hydrogen electrode (SHE) as the reference half-cell.
- Stoichiometry (A Level)
A Level stoichiometry notes: moles, formulas, limiting reagent, solutions and titrations, and gas calculations (pV = nRT) with strict units.
- Titration Calculations (A Level)
A Level titration arithmetic: a repeatable method from balanced equation to moles to concentration, with correct units and ratios.
- Transition Elements (A Level)
A Level transition elements notes: electron configurations, complex ions, variable oxidation states/redox, colour (d splitting), and catalysis.
- Transition Elements: Definition and Electron Configurations (A Level)
Apply both branches of the 9476 transition-element definition, write first-row atom and ion configurations, and explain the series’ physical trends.
- Transition-metal Catalysis (A Level)
Explain transition-element catalysis through surface adsorption or regenerated redox intermediates across the prescribed heterogeneous and homogeneous contexts.
- Variable Oxidation States and Redox Systems (A Level)
Explain variable oxidation states in transition elements, and write key redox half-equations for Fe, MnO4− and Cr2O7^2− with conditions and colour changes.
- Writing Redox Equations from Half-equations (A Level)
Combine half-equations into balanced overall redox equations, using E° values to decide which half-equation is reversed (oxidation).