Key term
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
Acids, Bases and Buffers
- 9 subtopics
- 22 things to know
- Components 01 and 03
What Acids, Bases and Buffers covers
Brønsted-Lowry acids and bases, Ka and pKa, calculating pH for strong and weak acids and for strong bases, how a buffer works and the one that controls blood pH, and the titration curves and the indicators that suit them.
Where it is assessed
Components 01 and 03
Periodic Table, Elements and Physical Chemistry, then the unified paper.
Check the OCR specification ↗The 9 subtopics
Each one has its own page.
- Brønsted-Lowry acids and bases and their reactionsRecall questions on Brønsted–Lowry acids and bases, conjugate acid–base pairs, monobasic, dibasic and tribasic acids, and the ionic equations for acids reacting with metals, carbonates, bases and alkalis.Open →
- Ka, pKa, pH and the ionic product of waterRecall questions on the Ka expression, what a larger Ka and a smaller pKa mean, the definition of pH, and the ionic product of water and its value at 25°C.Open →
- Calculating the pH of strong acids, strong bases and weak acidsRecall questions on pH from a strong monobasic acid, using Kw to reach pH for a strong base, and the two approximations behind the weak acid calculation.Open →
- pH and hydrogen ion concentrationRecall questions on converting each way between pH and hydrogen ion concentration, and on why a logarithmic scale is used at all.Open →
- What a buffer is and how it resists a change in pHRecall questions on the two ways a buffer is made, the role of the weak acid and of its conjugate base, and what happens when acid or alkali is added.Open →
- Buffer calculations and the buffer that controls blood pHRecall questions on calculating hydrogen ion concentration and pH from Ka and the two concentrations, and on the carbonic acid-hydrogencarbonate system in blood.Open →
- Titration curves, choosing an indicator and using a pH meterRecall questions on the features of each curve, what an indicator must satisfy, why no indicator suits a weak acid with a weak base, and calibrating a pH meter.Open →
- pH titration curves for the four acid-base combinationsRecall questions on the starting pH, the buffer region, the equivalence point and the final pH for each of the four combinations.Open →
- How an indicator works and choosing the right oneRecall questions on the indicator equilibrium, which form dominates in acid and in alkali, the colour change range, and matching an indicator to a titration.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Numbers
What forms when hydrogen ions react with hydroxide ions, what is the ionic equation, and what is the expression for Kₐ?
Numbers
How does pKₐ relate to acid strength, how is pH defined, and how is [H⁺] found from pH?
Numbers
What is the ionic product of water, what is its value at 25 °C, and how is [H⁺] found from [OH⁻] using Kw?
Key term
What approximation is made about [HA] at equilibrium for a weak monobasic acid, and when is it valid?
Numbers
Calculate the hydrogen ion concentration when acid dissociation constant = 1.00 × 10⁻⁵ mol dm⁻³, acid concentration = 0.200 mol dm⁻³.
Numbers
How is pH defined, what formula gives pH from [H⁺], and how is the hydrogen ion concentration recovered from a known pH?
Numbers
How is pH calculated from hydrogen ion concentration, what is the pH when [H⁺] = 1 mol dm⁻³, and why is a logarithmic scale used?
Process
What is a buffer solution, what does its weak acid do when hydroxide ions are added, and what does its conjugate base do when acid is added?
Numbers
How can the hydrogen ion concentration in a buffer be calculated?
Numbers
Calculate the pH when Ka value = 0.000829 mol dm⁻³, concentration of weak acid = 0.6 mol dm⁻³, concentration of salt = 0.96 mol dm⁻³.
Numbers
State the formula for calculating [H⁺] in a buffer solution.
Numbers
What is [H⁺] in a buffer with Kₐ = 0.000839 mol dm⁻³, a weak acid concentration of 0.95 mol dm⁻³ and a conjugate base concentration of 1.83 mol dm⁻³?
Numbers
What are two characteristic features of a pH titration curve for a weak acid with a strong base?
Numbers
What is a pH titration curve, and how does the pH begin and change in a strong acid-strong base titration?
Numbers
What is the pH at the equivalence point of a strong acid–strong base titration, what happens to the pH after the equivalence point, and why does a weak acid start at a higher pH?
Numbers
How steep is the vertical section of a weak acid–strong base curve compared with a strong acid–strong base one, and in a strong acid–weak base titration what is the initial pH and what happens at the equivalence point?
Numbers
What is the initial pH in a weak acid–weak base titration, how does the pH change during the titration, and which indicator suits a weak acid with a strong base?
Process
How does Le Chatelier's principle explain the behaviour of an indicator in acidic solution?
Key term
What colour does an indicator display in alkaline solution?
Numbers
State the acid dissociation constant expression.
Numbers
State the relationship between pKₐ and Kₐ.
Take Acids, Bases and Buffers further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Brønsted–Lowry acid vs Brønsted–Lowry base
Brønsted–Lowry acid: a species donating a proton. Brønsted–Lowry base: a species accepting a proton.
Strong acid vs Weak acid
Strong acid: a proton donor that fully dissociates in water. Weak acid: a proton donor that only partially dissociates in water.
Equivalence point vs End point
Equivalence point: stage where reactants have combined in the exact stoichiometric ratio. End point: stage where an indicator changes colour.
Questions from this topic
Each one with the model answer underneath.
- 1
Define a Brønsted–Lowry acid.
Model answer
A species that donates a proton.
- 2
Define a Brønsted–Lowry base.
Model answer
A species that accepts a proton.
- 3
What is a conjugate acid–base pair?
Model answer
Two species that differ by one proton.
- 4
When an acid donates a proton, what is formed?
Model answer
Its conjugate base.
- 5
When a base accepts a proton, what is formed?
Model answer
Its conjugate acid.
- 6
What is a monobasic acid?
Model answer
An acid that can donate one proton per molecule.
What is inside Levo
Six ways to work the same material.
Acids, Bases and Buffers revision questions
- What does Acids, Bases and Buffers cover in OCR A-Level Chemistry?
- 9 subtopics: brønsted-lowry acids and bases and their reactions, ka, pka, ph and the ionic product of water, calculating the ph of strong acids, strong bases and weak acids, ph and hydrogen ion concentration, what a buffer is and how it resists a change in ph, buffer calculations and the buffer that controls blood ph, titration curves, choosing an indicator and using a ph meter, ph titration curves for the four acid-base combinations and how an indicator works and choosing the right one. Each one has its own page with questions and model answers.
- How is Acids, Bases and Buffers organised?
- By the OCR H432 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Acids, Bases and Buffers, 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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