Process
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
Aromatic Compounds
- 6 subtopics
- 11 things to know
- Components 02 and 03
What Aromatic Compounds covers
Benzene's delocalised structure and the evidence for it, electrophilic substitution and the directing effects of substituents, and phenol, which reacts far more readily than benzene and shows why.
Where it is assessed
Components 02 and 03
Synthesis and Analytical Techniques, then the unified paper.
Check the OCR specification ↗The 6 subtopics
Each one has its own page.
- The delocalised model of benzene and the evidence for itRecall questions on the Kekulé and delocalised models, the overlapping p-orbitals, and the bond length and hydrogenation enthalpy evidence.Open →
- Nitration, halogenation and Friedel-Crafts reactions of benzeneRecall questions on the reagents for each, the nitronium ion and the halogen carrier, and why benzene resists bromination where an alkene does not.Open →
- The reactions of phenol, and directing effectsRecall questions on phenol with sodium hydroxide, with carbonates and with bromine water, and on which positions electron-donating and electron-withdrawing groups direct to.Open →
- Electrophilic substitution and directing effectsRecall questions on why substitution is favoured over addition, and on planning the order of steps in a disubstituted synthesis from the directing effects.Open →
- Phenol: acidity, bromination and nitrationRecall questions on the neutralisation with sodium hydroxide, distinguishing phenol from a carboxylic acid, and the mild conditions its bromination and nitration need.Open →
- Why phenol is more reactive than benzene, and planning a synthesisRecall questions on the oxygen lone pair donated into the ring, its effect on electron density, and using directing effects to sequence a multi-step synthesis.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Numbers
What is required for the halogenation of benzene, which species is the electrophile in nitration, and how does phenol react with sodium hydroxide?
Key term
What forms when phenol reacts with bromine water, is a catalyst needed, and what forms when phenol reacts with dilute nitric acid?
Key term
Give two examples of electron-donating groups and state which positions they direct substitution to.
Process
What is the characteristic reaction mechanism of aromatic compounds?
Key term
If a nitro group (–NO₂) is attached to a benzene ring at position 1, at which positions would a second substituent most likely be introduced?
Key term
What are 3-directing groups and which positions do they direct substitution to?
Key term
How can phenol be told apart from a carboxylic acid, does phenol need a halogen carrier to react with bromine water, and what temperature is needed?
Numbers
What concentration of nitric acid nitrates phenol, is a concentrated sulfuric acid catalyst needed, and which type of orbital holds the oxygen lone pair that activates the ring?
Key term
What does the donated oxygen lone pair do to the ring, and are the OH and NH₂ groups electron-donating or withdrawing?
Key term
To which position does an electron-withdrawing group such as NO₂ direct incoming electrophiles?
Take Aromatic Compounds further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Aliphatic compound vs Aromatic compound
Aliphatic compound: a carbon compound without an aromatic ring. Aromatic compound: a compound containing a stable delocalised ring system.
Electrophilic addition vs Electrophilic substitution
Electrophilic addition: an electron-pair acceptor adding across a multiple bond. Electrophilic substitution: an electron-pair acceptor replacing a hydrogen atom on an aromatic ring.
Questions from this topic
Each one with the model answer underneath.
- 1
What structure did Kekulé propose for benzene?
Model answer
A hexagonal ring with alternating single and double carbon-carbon bonds.
- 2
In the delocalised model of benzene, how do the p-orbitals on each carbon atom interact?
Model answer
The p-orbitals from each carbon atom overlap above and below the plane of the ring.
- 3
What type of system is formed when the p-orbitals in benzene overlap, and how is the electron density distributed?
Model answer
A delocalised π-system is formed, with electron density distributed equally around the ring.
- 4
What are the two ways benzene can be represented in structural diagrams?
Model answer
As a hexagon with a circle inside, or as a hexagon with alternating double bonds.
- 5
What is the carbon-carbon bond length in benzene, and how does this provide evidence for delocalisation?
Model answer
All C-C bond lengths are equal at 0.139 nm, which is intermediate between single bond length (0.154 nm) and double bond length (0.134 nm).
- 6
How does the enthalpy change of hydrogenation of benzene provide evidence for delocalisation?
Model answer
The enthalpy change of hydrogenation is less exothermic than expected for a structure with three isolated double bonds.
What is inside Levo
Six ways to work the same material.
Aromatic Compounds revision questions
- What does Aromatic Compounds cover in OCR A-Level Chemistry?
- 6 subtopics: the delocalised model of benzene and the evidence for it, nitration, halogenation and friedel-crafts reactions of benzene, the reactions of phenol, and directing effects, electrophilic substitution and directing effects, phenol: acidity, bromination and nitration and why phenol is more reactive than benzene, and planning a synthesis. Each one has its own page with questions and model answers.
- How is Aromatic Compounds organised?
- By the OCR H432 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Aromatic Compounds, 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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