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OCR A-Level Chemistry H432
Foundations in Chemistry
Topic overviewAtomic structure, isotopes and counting sub-atomic particlesRelative isotopic, atomic, molecular and formula massPredicting ionic charges and the common ionsWriting formulae, balanced equations and ionic equationsThe mole, molar mass and the Avogadro constantEmpirical and molecular formulae, and hydrated saltsGas volumes, concentration and the ideal gas equationStoichiometry, percentage yield and atom economyApparatus, and why high atom economy mattersMathematical skills and measuring mass, volume and gasAcids, alkalis, dissociation and neutralisationPreparing a standard solutionCarrying out a titration and its calculationsPlanning an experiment: variables, apparatus and recording resultsPractical safety, heating and filtrationUncertainty, percentage error, precision and accuracyEvaluating results: anomalies, conclusions, limitations and improvementsAssigning oxidation numbersRoman numerals in names, and the chlorate and nitrate ionsOxidation, reduction and metals reacting with acidsRedox equations and identifying what is oxidisedShells, orbitals and sub-shellsThe order in which sub-shells fillWriting electron configurations for atoms and ions
Bonding and Structure
Topic overviewIonic bonding and the properties of ionic compoundsCovalent and coordinate bondingLone pairs, bonding pairs and average bond enthalpyElectron pair repulsion theory, linear and trigonal planar shapesTetrahedral, pyramidal and non-linear shapes and their bond anglesOctahedral shapes, ions, and drawing molecules in three dimensionsElectronegativity, polar bonds and polar moleculesPermanent and induced dipoles, and hydrogen bondingSimple molecular lattices and why they melt easilySolubility and conductivity of simple molecular compounds
Periodic Table and Energy
Topic overviewPeriodicity and the electron configurations of periods 2 and 3The blocks, and first and successive ionisation energiesMetallic and giant covalent structures and their propertiesGroup 2 reactions with oxygen, water and acidsIonisation energy down Group 2 and the alkalinity of the hydroxidesUses of Group 2 compounds in agriculture and medicineThe halogens: boiling points, London forces and reactivityHalogen displacement reactions and the colours seenDisproportionation and the chlorination of waterTesting for halide ions with silver nitrate and ammoniaTesting for carbonate, sulfate and halide ionsTesting for ammonium ions and the order of the testsConcentration, pressure and measuring reaction rateCatalysts and their industrial importanceThe Boltzmann distribution, temperature and catalysts
Enthalpy Changes
Topic overviewExothermic and endothermic reactions and enthalpy profilesStandard conditions and the standard enthalpy changesBond enthalpies, q = mcΔT and calorimetryCalculating enthalpy change from bond enthalpiesWhy average bond enthalpies give only an approximationHess' law and enthalpy cycles from combustion and formation dataWorking through an enthalpy cycle and the sign conventionsCalorimetry and correcting for heat loss
Chemical Equilibrium
Basic Concepts of Organic Chemistry
Topic overviewIUPAC nomenclature and the alkyl groupsGeneral, structural, displayed and skeletal formulaeHomologous series, functional groups and saturationStructural isomers, bond fission and curly arrowsChain, position and functional group isomerismCurly arrows, homolytic and heterolytic fissionNucleophiles, electrophiles, radicals and the mechanism steps
Core Organic Chemistry
Topic overviewAlkanes: bonding, shape and boiling pointsCombustion of alkanes and their reaction with halogensThe radical substitution mechanism and its limitationsAlcohols: polarity, solubility and classificationOxidation, dehydration and substitution reactions of alcoholsHydrolysis of haloalkanes and comparing the ratesNucleophilic substitution and carbon-halogen bond strengthCFCs, radicals and the catalytic destruction of ozoneCombining analytical techniques to identify a compound
Alkenes
Topic overviewAlkenes: the double bond, sigma and pi bonding, and shapeE/Z and cis-trans isomerism in alkenesHydrogenation, halogenation and hydration of alkenesElectrophilic addition, carbocation stability and Markownikoff's ruleAddition polymerisation and repeat unitsWaste polymers, and biodegradable and photodegradable alternatives
Organic Synthesis
How Fast?
Topic overviewRate equations, order and the rate constantDeducing orders and finding the units of kWhat the rate equation reveals about the mechanismConcentration-time graphs and continuous monitoringHalf-life and the rate constant of a first-order reactionRate-concentration graphs and the initial rates methodClock reactions, colorimetry and analysing kinetic graphsThe rate-determining step and testing a proposed mechanismTemperature, the rate constant and the Arrhenius equationThe ln k against 1/T graph and finding the activation energy
Physical Chemistry and Transition Elements
Topic overviewMole fraction, partial pressure and ICE tablesKc and Kp expressions, their units and calculationsWhat changes the equilibrium constant, and the reaction quotientLattice enthalpy and the Born-Haber cycleEnthalpy of solution and hydration, and the effect of ionic charge and sizeEntropy and calculating entropy changeGibbs free energy and thermodynamic feasibility
Acids, Bases and Buffers
Topic overviewBrønsted-Lowry acids and bases and their reactionsKa, pKa, pH and the ionic product of waterCalculating the pH of strong acids, strong bases and weak acidspH and hydrogen ion concentrationWhat a buffer is and how it resists a change in pHBuffer calculations and the buffer that controls blood pHTitration curves, choosing an indicator and using a pH meterpH titration curves for the four acid-base combinationsHow an indicator works and choosing the right one
Redox and Electrode Potentials
Topic overviewOxidising and reducing agents, and balancing half-equationsCombining half-equations and using oxidation numbersRedox titrations and their calculationsStandard electrode potentials and setting up half-cellsThe electrochemical series and predicting feasibilityStorage cells and fuel cells
Transition Elements
Topic overviewLigands, complex ions and coordination numberElectron configurations from Sc to Zn, and which are transition elementsVariable oxidation states, coloured ions and catalysisThe shapes of complexes, stereoisomerism and cisplatinLigand substitution, haemoglobin and the copper complexesHydroxide precipitates of iron, manganese and chromiumRedox interconversions of iron, chromium and copperWhy ligand substitution happens and the changes it causesPrecipitation reactions written as aqua complexesDissolving hydroxides in excess ammonia and distinguishing the ions
Aromatic Compounds
Topic overviewThe delocalised model of benzene and the evidence for itNitration, halogenation and Friedel-Crafts reactions of benzeneThe reactions of phenol, and directing effectsElectrophilic substitution and directing effectsPhenol: acidity, bromination and nitrationWhy phenol is more reactive than benzene, and planning a synthesis
Organic Chemistry and Analysis
Topic overviewOxidation and reduction of carbonyls, and the addition of HCNThe nucleophilic addition mechanism2,4-DNPH and Tollens' reagentCarboxylic acids: solubility and reactions with metals, carbonates and basesEsterification and the hydrolysis of estersAcyl chlorides and their reactions with alcohols, amines and ammoniaAmines as bases, and preparing aliphatic aminesSecondary and tertiary amines, and preparing aromatic aminesAmino acids, their reactions, and amidesOptical isomerism and identifying a chiral centreCondensation polymerisation and the ester and amide linkagesHydrolysing condensation polymers and telling them from addition polymersNitriles from haloalkanes and from carbonyl compoundsFriedel-Crafts reactions and lengthening the carbon chainThin-layer and gas chromatography, Rf values and retention timesTest-tube tests for the organic functional groupsTests for the inorganic ions and interpreting chromatograms
Spectroscopy
Topic overviewCarbon-13 and proton NMR: peaks, chemical shift and integrationSpin-spin splitting and predicting a spectrumTMS, deuterated solvents and the D₂O shakeCombining elemental analysis, mass spectrometry, IR and NMRMolecular formula from the molecular ion, and fragmentation lossesWhat IR and NMR each contribute to a structureInfrared absorption, global warming and breathalysersA systematic approach and the degree of unsaturation
How Fast?
- 10 subtopics
- 19 things to know
- Components 01 and 03
What How Fast? covers
Kinetics beyond collision theory: rate equations, orders and the rate constant, reading order from concentration-time and rate-concentration graphs, what the rate equation reveals about the mechanism, and the Arrhenius equation.
Where it is assessed
Components 01 and 03
Periodic Table, Elements and Physical Chemistry, then the unified paper.
Check the OCR specification ↗The 10 subtopics
Each one has its own page.
- Rate equations, order and the rate constantRecall questions on the meaning of order, the overall order, the role of k, half-life, and how rate depends on concentration for each order.Open →
- Deducing orders and finding the units of kRecall questions on reading order from initial rates data, the general form rate = k[A]ᵐ[B]ⁿ, why orders cannot be read off the balanced equation, and deriving the units of k.Open →
- What the rate equation reveals about the mechanismRecall questions on which species appear in the rate equation and why one may not, and on the principle and advantage of the initial rates method.Open →
- Concentration-time graphs and continuous monitoringRecall questions on the shapes for zero and first order, why a tangent rather than a chord is used, and what continuous monitoring offers.Open →
- Half-life and the rate constant of a first-order reactionRecall questions on the constant half-life of a first-order reaction, reading it from a graph, and k = ln 2 / t½.Open →
- Rate-concentration graphs and the initial rates methodRecall questions on the shapes for zero, first and second order, and on what the gradient of a linear rate-concentration graph gives.Open →
- Clock reactions, colorimetry and analysing kinetic graphsRecall questions on what a clock reaction approximates, how colorimetry follows a rate, and choosing scales, reading intercepts and drawing tangents.Open →
- The rate-determining step and testing a proposed mechanismRecall questions on what the rate-determining step is, what the orders imply about it, and the two criteria a proposed mechanism must satisfy.Open →
- Temperature, the rate constant and the Arrhenius equationRecall questions on why raising the temperature raises k, and on what Eₐ, A, R and T each represent in the Arrhenius equation.Open →
- The ln k against 1/T graph and finding the activation energyRecall questions on the logarithmic form, which graph is plotted, and what its gradient and intercept give.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
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How does rate depend on concentration for a zero-order, a first-order and a second-order reactant?
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If doubling a concentration quadruples the rate, what is the order, what is the general rate equation for reactants A and B, and what decides the units of k?
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Can the orders in a rate equation be predicted from the balanced chemical equation? Explain.
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Which species from a reaction mechanism will appear in the rate equation?
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What does a zero-order concentration–time graph look like, how does a first-order graph differ, and why is a tangent used rather than a chord?
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What is characteristic of the half-life of a first-order reaction, how is it read off a concentration–time graph, and what do equal successive half-lives show?
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What equation links k to the half-life, when does it apply, and what is k when t½ = 280 s?
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How is first-order dependence recognised on a rate–concentration graph, why does its gradient give k, and what does a zero-order reactant give?
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What is continuous monitoring in the context of reaction kinetics?
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Give an example of a technique used for continuous monitoring of reaction rates.
Process
A reaction is second order with respect to reactant A. What does this suggest about the mechanism?
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If a species appears in the balanced equation but has zero order in the rate equation, what does this indicate about the mechanism?
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What type of experimental evidence is used to propose and support reaction mechanisms?
Process
How does raising the temperature change molecular energies, and why does that speed up the reaction?
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What does T represent in the Arrhenius equation and in what units, what is its logarithmic form, and what does A represent?
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What does R represent in the Arrhenius equation, which graph is plotted to obtain a straight line, and what does its gradient equal?
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State the formula used to calculate the pre-exponential factor from the y-intercept of an Arrhenius plot.
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State the general rate equation and interpret its powers.
Take How Fast? further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Rate constant vs Reaction rate
Rate constant: proportionality constant linking rate with reactant concentrations. Reaction rate: change in concentration of a reactant or product per unit time.
Order of reaction vs Overall order
Order of reaction: power to which a concentration is raised in a rate equation. Overall order: sum of concentration powers in a rate equation.
Rate-determining step vs Elementary step
Rate-determining step: slowest stage controlling the overall reaction rate. Elementary step: one stage in a multi-stage reaction mechanism.
Questions from this topic
Each one with the model answer underneath.
- 1
How is rate of reaction defined in terms of concentration?
Model answer
Rate of reaction is the change in concentration of a reactant or product per unit time.
- 2
What does the order with respect to a reactant represent in a rate equation?
Model answer
The order with respect to a reactant is the power to which the concentration of that reactant is raised in the rate equation.
- 3
How is the overall order of a reaction determined from the rate equation?
Model answer
The overall order is the sum of the individual orders with respect to each reactant in the rate equation.
- 4
What is the role of the rate constant k in a rate equation?
Model answer
The rate constant k is the proportionality constant that relates the rate to the concentrations of reactants raised to their respective orders.
- 5
Define half-life in the context of chemical kinetics.
Model answer
Half-life is the time taken for the concentration of a reactant to fall to half its initial value.
- 6
What happens to the rate of reaction if the concentration of a zero-order reactant is increased?
Model answer
The rate remains unchanged; changing the concentration of a zero-order reactant has no effect on the rate.
What is inside Levo
Six ways to work the same material.
How Fast? revision questions
- What does How Fast? cover in OCR A-Level Chemistry?
- 10 subtopics: rate equations, order and the rate constant, deducing orders and finding the units of k, what the rate equation reveals about the mechanism, concentration-time graphs and continuous monitoring, half-life and the rate constant of a first-order reaction, rate-concentration graphs and the initial rates method, clock reactions, colorimetry and analysing kinetic graphs, the rate-determining step and testing a proposed mechanism, temperature, the rate constant and the arrhenius equation and the ln k against 1/t graph and finding the activation energy. Each one has its own page with questions and model answers.
- How is How Fast? organised?
- By the OCR H432 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in How Fast?, on a schedule.
Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.
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