Scholarship Chemistry 93102

Bonding, thermochemistry, equilibrium, acids and bases, redox, organic and spectroscopy. Unfamiliar contexts with hints, strategy prompts, worked steps and s/o marking.

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TierAll Bridge Scholarship

Particles, bonding and structure · 50

Phosphorus chlorides: molecules and ionsLewis structures, shape, polarity and bondingBridge
Electrons, ionisation energies and the size of ionsElectron configuration, ionisation energy trends, ionic radiiBridge
Why substances melt, boil and dissolve differentlyTypes of solids, intermolecular forces, dissolvingBridge
Shapes beyond the octet: SF4, ClF3, XeF4 and I3⁻Shapes with five and six electron regions including lone pairs; polarityBridge
Why water is so unusualTrends in boiling points of hydrides; hydrogen bondingBridge
Calcium chloride on icy roadsIon charge and radius, dissolving energetics, Hess's law with hydrates, entropyScholarship
The 'inert' gas that isn't: xenon compoundsShapes of noble-gas compounds, IE trends, bond enthalpy from ΔfH, energetics of decompositionScholarship
Trends across Period 3 and the first transition seriesTrends in radius and electronegativity; bond polarity; transition metal configurationsBridge
What dissolves in what?Predicting solubility from particles and intermolecular forcesBridge
Diamond, graphite, graphene, C60 — and siliconStructure–property relationships of carbon and silicon allotropes; atomisation from bond enthalpiesScholarship
Hydrofluoric acid: weak but dangerousHydrogen bonding; acid strength vs bond enthalpy; quadratic pHScholarship
Shapes of polyatomic ionsLewis structures and shapes of polyatomic ionsBridge
Reading ionisation energy dataSuccessive ionisation energies; Period 3 first-IE anomalies; energy to form ionsScholarship
Five compounds, same mass, different boiling pointsRanking boiling points of organic compounds of similar Mr; enthalpy of vaporisationScholarship
Five solids, four kinds of bondingProperties of ionic, covalent network, metallic and molecular solidsBridge
Polar or non-polar?Molecular polarity from bond polarity and shapeBridge
Electron configurations of the first transition seriesElectron configurations including Cr and Cu anomalies; transition metal ions; colourBridge
Why water is weirdHydrogen bonding explains water's anomalous boiling point, density and heat capacityScholarship
CFCs and the ozone holeShape and polarity of halomethanes; bond enthalpy and photodissociation; replacement compoundsScholarship
Iodine's halogen compounds and ionsLewis structures, shapes and bond angles for expanded-octet ions and molecules; lone-pair placement; polarityScholarship
cis- and trans-1,2-dichloroetheneGeometric isomers: requirements, polarity and boiling points; isomerisation equilibriumScholarship
Antimony halides and the strongest acid knownLewis structures and shapes of antimony halides and halide ions; effect of accepting a halide ion on shape; superacid behaviour of HF/SbF5; Hess calculation from enthalpies of formationScholarship
Phosphorus fluorides in a lithium-ion batteryShapes of PF3, PF5, PF6⁻ and POF3; testing the VSEPR shape of PF5 against bond-length and ¹⁹F NMR data; dispersion vs dipole attractions; LiPF6 electrolyte and HF from trace waterScholarship
Sulfuryl fluoride: a fumigant for log exportsLewis structures and shapes of sulfur oxyfluorides with S=O double bonds; position of a double bond in a trigonal bipyramid; polarity and boiling point; fumigant dose and scrubbing stoichiometryScholarship
Ten electrons each: the neon-like ionsIsoelectronic series: radius and electron-removal energy versus nuclear charge; endothermic formation of O²⁻; testing a charge/radius model against lattice enthalpiesScholarship
Gallium: the element hiding behind the d-blockIE anomalies (Zn → Ga), poor shielding by 3d electrons (Al vs Ga), Hess calculation for a thermite-type reaction, evaluating an IE-based explanation with ion-size dataScholarship
Ionic liquids: salts that melt below room temperatureIonic liquids: ion size, charge spreading and packing vs melting point; ions vs molecules for volatility and conduction; yield calculation; ion concentration vs ion mobilityScholarship
Boron compounds: from 'white graphite' to hydrogen storageBoron compounds: layered BN vs graphite, molecular BF₃ and B(OH)₃, ionic NaBH₄; boric acid as a weak (Lewis) acid; hydrogen yield from NaBH₄Scholarship
How much titanium dioxide is in white paint?spd configurations of Ti, Fe and Zn ions; d–d colour; Ti(IV)/Ti(III) redox with E°; Jones-reductor titration with concordant titres; evaluating sources of errorScholarship
Four fluorides beyond the octetElectron counting, shapes, bond angles and polarity for KrF₂, AsF₅, BrF₅ and SF₆; gas density from molar massBridge
Halomethanes and methanol: what really sets the boiling pointDispersion vs permanent dipole attractions down the halomethanes; hydrogen bonding in methanol; enthalpy of vaporisationBridge
Selenium's fluorides and fluoro-ionsExpanded-octet VSEPR across a family of ions and molecules; evaluating VSEPR against measured bond lengths and angles; polarity and physical state; percentage yieldScholarship
Bromine trifluoride: freeing oxygen from rocksExpanded-octet VSEPR across a cation/molecule/anion family; evaluating VSEPR against BrF3 bond data; self-ionisation and conductivity of a molecular liquid; reacting-mass and gas-volume calculationScholarship
Tellurium chlorides: when VSEPR meets the dataExpanded-octet shapes of a cation/molecule/anion series; identifying a salt from gravimetric data and judging precision; evaluating VSEPR for a seven-pair ion; ionic vs molecular behaviour of TeCl4Scholarship
Second ionisation energies from lithium to neonElectron configurations of atoms and +1 ions; explaining anomalies in first and second ionisation energies; energy calculations from IE data; evaluating a generalisationScholarship
Down Group 2: from Ōamaru limestone to magnesiteTrends in atomic radius, ionic radius, IE and metallic melting point down Group 2; thermal decomposition of carbonates from ΔfH and ΔS; polarising powerScholarship
A salt that is liquid at room temperatureClassifying substances by particles and attractions; explaining melting points of ionic compounds with large, irregular ions; neutralisation calorimetry and its errorsScholarship
Four faces of ironMolar mass from vapour density; dative bonding in Fe2Cl6 and Fe(CO)5; ionic vs covalent character; dimer–monomer equilibrium from data; classifying solidsScholarship
Silver halides: how ionic are they?Born–Haber cycles with states; comparing experimental and ionic-model lattice enthalpies; covalent character from polarisation; solubility from lattice and hydration enthalpiesScholarship
Lewis diagrams of five everyday ionsCounting valence electrons in ions; Lewis diagrams with lone pairs; shapes and bond angles from electron regionsBridge
Six molecules: polar or non-polar?Bond polarity from electronegativity difference; molecular shape; cancellation of bond dipoles; lone-pair contribution to dipole momentBridge
Tin chlorides and the dyer's 'pink salt'VSEPR for a tin(II)/tin(IV) chloride series with expanded octets; bonding vs volatility; gravimetric purity and gas-volume calculations; evaluating a gravimetric methodScholarship
Chlorine trifluoride: the fluorinating agent that sets sand alightShapes of chlorine fluoride molecules and ions (5 and 6 electron regions); mean bond enthalpies from formation data; reactivity of hypervalent fluorides; IMF in UF6 vs ClF3Scholarship
Xenon fluoride ions and a mixture to analyseShapes of xenon fluoride cations and anions including a 7-region ion; fluoride-ion transfer equations; analysing an XeF2/XeF4 mixture from a gas volume; evaluating the sensitivity of the analysisScholarship
Iodine's oxoacids: resonance, bond lengths and acid strengthExpanded-octet Lewis structures and resonance in iodine oxyanions; bond order vs bond length; pH of a weak acid and of a moderately strong acid (approximation test); structure and acid strength of iodine oxoacidsScholarship
Iron and manganese in bore waterspd configurations of Mn and Fe ions; third IE anomaly (half-filled d5); E°cell for air oxidation; disproportionation of Mn3+; permanganate dose calculation; evaluating dosingScholarship
Red flares: identifying element ZIdentifying an element from successive IEs and gravimetric data; spd configurations and first-IE comparisons; energetics of ion charge; evaluating a thermal-decomposition methodScholarship
Five ions shaped like kryptonIsoelectronic radius series (Kr configuration); percentage radius changes; ionic substitution in minerals; enthalpy of solution from lattice and hydration enthalpies; charge-density reasoningScholarship
Three phosphorus allotropes and the safety matchStructure, bonding and properties of white, red and black phosphorus; mean P–P bond enthalpies from formation data; bond-angle strain; reactivity and safety linked to structureScholarship
Configurations of cobalt, vanadium, selenium and scandium ionsspd configurations of transition-metal and p-block atoms and ions; order of filling vs order of removal; successive IEs and maximum ion chargeBridge

Thermochemistry · 40

Three ways to find the enthalpy of combustion of ethanolHess's law, calorimetry and bond enthalpiesBridge
The cold pack: an endothermic process that happens by itselfEntropy of system and surroundings, spontaneity, calorimetryBridge
Enthalpies you can't measure directlyHess's law from combustion data; fuel valuesBridge
Enthalpy of neutralisation in a polystyrene cupCalorimetry of neutralisation; strong vs weak acids; experimental designBridge
Methanol as a liquid carrier for hydrogenΔH by two methods, entropy and temperature, Kc and Q, fuels and intermolecular forcesScholarship
How efficient is a camping stove?ΔcH theory vs experiment with calorimeter heat capacity, incomplete combustion energetics, fuel storageScholarship
Hydrogenating etheneΔH by bond enthalpy and ΔfH; energy diagrams; catalystsBridge
Will it happen by itself?Predicting entropy changes and spontaneity from ΔH and ΔSBridge
Hydrazine: a rocket fuelΔH from ΔfH for propellants; energy per kg; Lewis structure, shape and hydrogen bonding; entropyScholarship
Thermite welding of railway linesΔH of a solid-state redox reaction, energy per gram, activation energy, ionic melting pointsScholarship
Cold packs and potassium nitrateΔH of solution by calorimetry; link to solubility and entropyBridge
Calcium carbide and acetylene: Hess's law from mixed dataHess's law combining enthalpies of formation and combustion; energy per kilogram; entropy of system and surroundings; evaluating hazards from thermochemical dataScholarship
Which propanol is more stable?ΔfH from ΔcH via Hess's law; isomer stability; limits of bond-enthalpy reasoningScholarship
Self-heating coffee cansΔH from ΔfH; reactant mass for a heating requirement with efficiency; entropy; safetyScholarship
How good is a spirit burner?Enthalpy of combustion from a spirit burner; efficiency; errorsBridge
ΔfH of methane from combustion dataHess's law cycle from combustion dataBridge
Melting ice in a drinkEnergy for melting and heating; intermolecular forces during phase changeBridge
Hydrogen or natural gas?Energy per gram vs per litre for gaseous fuels; storage linked to intermolecular forcesScholarship
The reaction that freezes a beaker to the benchSpontaneous endothermic reaction; entropy; energy absorbed and temperature changeScholarship
Why bond enthalpies underestimate ΔcH of ethanolΔcH from bond enthalpies; correcting for states; reconciling with dataScholarship
Making syngas from coalEndothermic, entropy-increasing equilibrium; heterogeneous Kc; temperature choiceScholarship
Bioethanol: how much energy survives fermentation?ΔH by Hess from combustion data; theoretical yield; energy retained; evaluating biofuelScholarship
Titanium by the Kroll process: Hess's law from mixed dataHess's law from a measured reaction enthalpy, combustion enthalpies and formation enthalpies; coupling an unfavourable reaction to a favourable one; energy per kilogram; redox and entropy in an industrial reductionScholarship
Airbags and sodium azide: energy in a split secondFormation enthalpies from two measured reaction enthalpies; writing an overall equation from a description; gas volume and mass stoichiometry; Lewis structure and shape of the azide ion; bond enthalpy argument; evaluating a chemical designScholarship
Solar-grade silicon: from quartz to pure rodsBond-enthalpy estimates checked against data; formation enthalpy from a measured reaction; Hess's law across a three-step purification; entropy and the minimum temperature for an endothermic reaction; evaluating industrial conditions; oxidation numbers in a hydrideScholarship
Dimethyl ether: one combustion, three enthalpiesΔcH from calorimetry, from formation enthalpies (liquid and gaseous water) and from bond enthalpies; comparing the three values and evaluating sources of difference; isomer energetics linked to intermolecular forcesScholarship
Does ammonium chloride really sublime?ΔrH and ΔS_sys from data; ΔS_surr and ΔS_total at two temperatures; changeover temperature; explaining observations in a heated tube with entropy and rates of diffusion; evaluating a textbook claimScholarship
Cyclopropane: when bond enthalpies get it wrongΔfH from combustion data; ΔfH estimated from bond enthalpies via atomisation; explaining a large discrepancy with bond angles (ring strain); evaluating bond-enthalpy predictions; spontaneity versus rateScholarship
Calibrate the cup first: iron and copper(II) sulfateFinding the heat capacity of a calorimeter by mixing water samples; including it in q; energy released as a positive quantity; ΔrH from the limiting reagent; evaluating heat loss and other errorsBridge
Nitric acid from ammonia: Hess's law along the Ostwald routeHess's law from a measured reaction enthalpy, enthalpies of formation and ΔvapH; selectivity of a catalyst versus thermodynamics; nitrogen oxidation states and disproportionation; entropy and temperature; scaling per tonneScholarship
Glenbrook ironsand: how much coal does magnetite need?Hess's law from ΔcH, measured ΔrH and ΔfH; mixed-valence oxide; endothermic but spontaneous gas-forming reaction; energy and carbon budget per tonneScholarship
Contact-lens peroxide: one ΔH, three valuesDisproportionation half-equations; ΔrH by bond enthalpies, by ΔfH and by calorimetry; correcting a gas-phase estimate for states; evaluating an experimental value with a revised concentrationScholarship
Magnesium displacing zinc: reading the data-logger traceDisplacement reaction: E°cell and observations; temperature–time graph extrapolated to the time of mixing; correcting for a side reaction; evaluating accuracy against ΔfH dataScholarship
Fire-extinguisher powder: an enthalpy you cannot measure directlyHess cycle from two acid reactions; extrapolating an endothermic and an exothermic cooling curve; propagating uncertainty; steam correction; entropy of a gas-forming decompositionScholarship
Gib board: plaster that sets and walls that resist fireΔrH of hydration and dehydration from ΔfH; entropy of hydrate formation and of dehydration with temperature; energy and water released from a wall; water of crystallisation in a partly set plasterScholarship
Urea from Taranaki gas: a two-step Hess problemHess's law from combustion and formation data; two-step industrial process; energy per tonne; conditions from enthalpy, gas moles and rate; evaluating a mismatch between data setsScholarship
Blasting rock: ANFO versus nitroglycerineBalancing an equation from a description; oxygen balance; energy per kg and per L from formation enthalpies; comparing explosives and fuels; consequences of off-balance mixturesScholarship
Green steel: hydrogen or carbon to reduce iron ore?ΔrH per mole of product for two industrial routes; reductant, CO2 and electricity per tonne; evaluating a sustainability claim; equilibrium and flow arguments for a gas–solid reductionScholarship
A trampers' flameless heater in the calorimeterCalorimeter heat capacity by method of mixtures; cooling-curve extrapolation; ΔrH from experiment vs formation data; evaluating validity and accuracy; comparing heat sources per mol and per kgScholarship
Propan-2-ol from propene: two Hess cyclesHess cycles from combustion data and from formation data; ΔfH from ΔcH; adjusting for changes of stateBridge

Organic chemistry · 60

From propene to an esterReaction scheme: addition, substitution, elimination, oxidation, esterificationBridge
Nylon-6,6 and peptidesCondensation polymers, amide hydrolysis, optical isomersBridge
Isomers of C4H8 and C4H10OStructural, geometric and optical isomerism; alcohol classes; eliminationBridge
Ethanoyl chloride: a reactive starting pointAcyl chloride reactions, amines as bases, amidesBridge
A student's route to N-ethylethanamideEvaluating and correcting a synthesis; amines and amidesBridge
Plastics that last and plastics that break downAddition vs condensation polymers; polyester hydrolysisBridge
A fruity ester that rotates lightDeducing structures from reactions and data; chirality through a reaction; ester synthesis and safetyScholarship
Lactic acid: from yoghurt to compostable plasticBifunctional molecules, polyesters from one monomer, distinguishing isomers, titrationScholarship
Names, structures and functional groupsIUPAC naming, drawing from names, functional groups, types of structural isomerismBridge
What happens to a haloalkane depends on the conditionsClassifying haloalkanes; substitution vs elimination; major/minor alkenesBridge
Five unlabelled bottlesPlanning a sequence of chemical tests to identify unlabelled compoundsBridge
Fishy smells and lemon juiceAmine basicity and pH; salts; amide hydrolysis; amide formationBridge
Left-handed and right-handed moleculesRecognising chiral centres; drawing enantiomers; properties of enantiomersBridge
From fruity esters to soapEster formation, hydrolysis, saponification, percentage yieldBridge
One alcohol, five reactionsReactions of alcohols with a range of reagentsBridge
Adding across a double bondAddition reactions of alkenes; Markovnikov; tests; addition polymersBridge
Planning routes from 1-bromopropaneMulti-step synthesis planning with reagents and conditionsBridge
Making and testing aspirinEster formation from an anhydride, yield, purity by titration, IR evidence of reactionScholarship
Biodiesel from meat-works tallowTransesterification, soap formation side reaction, free fatty acid titration, viscosityScholarship
Identifying an amide from its piecesDeducing an amide from hydrolysis products, titration Mr, ¹³C symmetry and IRScholarship
Hydrating propeneHydration of propene: major/minor, yield, separation by boiling point, spectroscopic confirmationScholarship
Why ibuprofen is sold as a saltChiral drugs, salt formation, ionisation vs pH and absorptionScholarship
Aldehyde or acid? Controlling an oxidationControlling oxidation products by apparatus; redox stoichiometry; boiling points; IR monitoringScholarship
A student's route from propene to propanamideCritiquing a synthesis scheme: Markovnikov hydration, reflux vs distillation, acid vs acyl chloride with ammonia; multi-step yieldScholarship
Four reactions in one flaskFollowing a multi-step sequence on unseparated mixtures; major/minor products; distinguishing final productsScholarship
Two amides, one formula: X and YDeducing two isomeric amides from percentage composition, hydrolysis products, molar masses and described IR / ¹³C dataScholarship
Up or down the oxidation ladderChoosing NaBH4 or acidified dichromate; oxidation vs reduction; reflux vs distillation; percentage yieldBridge
Syntheses from a short reagent shelfDesigning syntheses from a restricted reagent list (NaBH4 reduction, oxidation, SOCl2, NH3); convergent route; limiting reagent across branches; racemic productsScholarship
Refinery off-gas: two alkenes, one flaskFollowing HBr addition, hydrolysis and oxidation through an unseparated two-alkene mixture; major/minor; product masses; separation by boiling point; 13C NMR vs IRScholarship
Fusel oil: from sweaty socks to fruitHydration, oxidation and esterification carried through an unseparated alkene/alcohol mixture; major/minor; masses; esterification equilibrium; work-up and separationScholarship
A student's route to antifreezeCritiquing a three-step route to a diol: hydrogen halide vs halogen addition, aqueous vs alcoholic KOH; products of the wrong reagents; yield; comparing with one-step permanganate oxidation; 13C NMR and IR to identify productsScholarship
Making the amine in a farm herbicideCritiquing a route to a primary amine: oxidation vs dehydration, halogen vs hydrogen halide addition, ammonia stoichiometry and multiple substitution; yield; mass-spectrum chlorine isotope patternsScholarship
A perfumer's single bottle of 2-methylpropanalRestricted-reagent routes from one aldehyde: moving the oxygen from a primary to a tertiary carbon (reduction, dehydration, hydration); convergent ester route via an acyl chloride; NaBH4 stoichiometry; which branch runs out; acyl chloride vs acid-catalysed esterificationScholarship
Which nylon is in the fishing net?Polyamide repeating unit and acid hydrolysis; identifying a dicarboxylic acid monomer from titration data (concordant titres, molar mass); purity; validity and accuracy; hydrogen bonding between polymer chainsScholarship
Is the PET flake pure enough to unzip?Alkaline hydrolysis of a polyester; back titration to find purity; indicator choice using pKa of the hydrolysis product; error propagation in a difference methodScholarship
Natural or nature-identical?Following a chiral centre through oxidation, acyl chloride formation and esterification; loss of chirality on elimination and racemic addition products; blend composition from polarimetry; yieldScholarship
Reflux or distil, aqueous or alcoholic?Reagents and conditions: KOH(aq) vs KOH in ethanol; reflux vs distillation for oxidation; the two roles of concentrated sulfuric acid; tertiary alcoholsBridge
Five isomers of C3H5ClEmpirical and molecular formula from percentage composition and MS; constitutional (structural) and geometric isomers of C3H5Cl; requirements for cis–trans isomerism; Markovnikov addition and chiralityBridge
Shifting a carbonyl group: a route that cannot workCarrying an unseparated mixture through dehydration, HBr addition, substitution and oxidation when neither Zaitsev nor Markovnikov discriminates; yield chain; evaluating separation by boiling point and 13C shiftsScholarship
A tetrasubstituted alkene and a trace of primary alcoholElimination from a tertiary haloalkane with a tetrasubstituted Zaitsev product, convergent Markovnikov hydration, selective dichromate oxidation of a trace primary alcohol; electron counting; evaluating an analytical resultScholarship
A borohydride, a dehydration and the wrong nucleophileCritiquing a synthesis scheme with reagent-confusion errors (NaBH4 vs KOH(aq), conc. H2SO4 vs dichromate, alcohol vs amine with an acyl chloride); products of the wrong reagents; multi-step yield and amine stoichiometry; ester vs amide by IR, 13C and hydrolysisScholarship
Making a honeybee alarm signal with borohydride and permanganateDesigning syntheses from a restricted reagent list: NaBH4 reduction, permanganate oxidation, acyl chloride ester and amide formation; limiting reagent across branches; spectroscopic monitoringScholarship
A solvent ketone and its derivativesDeducing six related C6 compounds from combustion analysis, chemical tests, IR, 13C NMR, MS and stereochemical observations; ruling out isomeric ketones; racemic products from planar intermediatesScholarship
An unsaturated ester, a back titration and five relativesSaponification back titration with concordant titres; deducing an unsaturated chiral ester and its hydrolysis products from tests and spectra; elimination major/minor with geometric isomersScholarship
Pear flavour: why the acid is in excessEster preparation where the alcohol and ester boil 5 °C apart: choice of excess reagent, reflux vs distillation, carbonate wash, drying, distillation; Kc-limited yield vs actual yield; acyl chloride alternative and hazardsScholarship
Making sandfly repellent: DEET from an acyl chlorideAcyl chloride route to a tertiary amide (DEET): SOCl2 under anhydrous reflux, 1 : 2 amine stoichiometry, acid/base washes, IR evidence of impurity; limiting reagent with density dataScholarship
Eight bottles, eight functional groupsNaming eight functional groups by NZQA conventions; classifying reactions (substitution, elimination, addition, oxidation, hydrolysis, condensation, acid–base); optical and geometric isomers; percentage yieldBridge
Water or ethanol as solvent: two branched haloalkanesHaloalkane reactions: substitution with KOH(aq) and NH3, elimination with alcoholic KOH; Zaitsev major/minor; which alkene shows geometric isomerism; chirality of products; mass of major productBridge
Two butanols, two amides and a gasCarrying a primary/tertiary alcohol mixture through SOCl2, ammonia and an acyl chloride; substitution vs elimination of primary and tertiary chloroalkanes; branch-by-branch amounts; gas volume; distinguishing isomeric amidesScholarship
A mislabelled cylinder of butenesHydration of a but-1-ene/but-2-ene mixture; oxidation of the alcohol mixture under reflux; dichromate stoichiometry; NaHCO3 wash; distillation vs reflux judged from boiling points; chirality and geometric isomersScholarship
A student's apple flavour from one alcoholCritiquing an ester synthesis from one alcohol: distillation vs reflux, HCl cannot make an acyl chloride, water hydrolyses acyl chlorides, checking a correct spectroscopic claim; products of the wrong reagents; limiting reagent and optimum splitScholarship
Levulinic acid: one molecule, two functional groupsSelective reactions of a keto-acid with a fixed reagent list: NaBH4 reduces the ketone but not the acid, carboxylate or amide; intramolecular esterification to a lactone; SOCl2 attacks both COOH and OH, so order matters; NaBH4 stoichiometry; chirality of productsScholarship
Poly(butylene succinate): a compostable polyesterPolyester from a diol and a diacyl chloride or diacid; repeating unit; back titration of a polymer by alkaline hydrolysis; atom economy; equilibrium and rate in polymerisation; biodegradabilityScholarship
Silk fibroin: a natural polyamideProtein (natural polyamide) hydrolysis: amino-acid mole ratios from mass data, water taken up on hydrolysis, repeating sequence; ionic forms in acid and base; optical activity of hydrolysatesScholarship
Dating buried shells by racemisationRacemisation of an amino acid through a planar intermediate; equilibrium constant of 1 for enantiomers; D/L ratio, optical rotation and age from a given rate equation; effect of temperature and contamination on the resultScholarship
Four hexenes and the chirality of their HBr productsIdentifying four C6H12 alkenes from ¹³C peak counts, geometric isomerism and the chirality of HBr addition products; fate of chirality in substitution vs elimination; Mohr titration of bromide after hydrolysis with concordant titresScholarship
Recovering methylamine from an amideAmide hydrolysis in acid and base; distillation of a volatile amine into acid and back titration; pH at the end point from the pKa of the amine conjugate acid; indicator choice; basicity of amines vs ammonia vs amides; amine saltsScholarship
Heptan-1-ol: a map of reaction typesClassifying and carrying out oxidation, substitution, elimination and addition starting from heptan-1-ol; Markovnikov product vs substitution product; primary vs secondary alcohol oxidation; distillation vs reflux; dichromate stoichiometryBridge
Making a feijoa flavour: ethyl butanoateEster preparation: limiting reagent and yield, equilibrium-limited maximum yield from Kc, justifying reflux/distillation/washing, acid vs base hydrolysis, spectroscopic purity checkScholarship
Aspartame: a sweetener that falls apartDipeptide ester: hydrolysis products, mass of methanol, ionisation of –COOH/–NH₃⁺ vs pH, evaluating stability data, effect of temperature and pH on breakdownScholarship

Spectroscopy · 30

Identifying an ester, C4H8O2Structure from IR, ¹³C NMR and mass spectraBridge
Three isomers of C3H6ODistinguishing isomers using IR, ¹³C NMR, MS and chemical testsBridge
Seven isomers of C4H10OIdentifying alcohol/ether isomers with IR, ¹³C NMR, MS and optical activityBridge
From soot-free combustion to a structureEmpirical formula from combustion data, molecular formula from MS, structure from IR/¹³C/MSScholarship
Four IR spectra, four compoundsAssigning IR absorptions to functional groups; matching spectraBridge
Counting carbons that 'look the same'Counting ¹³C environments; using shift ranges; matching spectraBridge
Reading a mass spectrum: chlorine's fingerprintMolecular ions, isotope patterns of chlorine, fragment ionsBridge
Three isomers of C3H8OCombining IR and ¹³C NMR to identify isomersBridge
Same molecular ion, different fragmentsUsing fragmentation patterns to distinguish isomeric carbonyl compoundsBridge
An acid and two esters with the same formulaDistinguishing an acid and two esters with IR, ¹³C and MSBridge
Which chlorobutane?MS isotope pattern, ¹³C symmetry, reaction products of a tertiary haloalkaneScholarship
A chiral alcohol with a double bondCombustion analysis, IR, ¹³C, chirality and MS to identify an unsaturated alcoholScholarship
Sorting plastic waste by spectroscopyIdentifying polymers by IR and hydrolysis; mass of monomer from hydrolysisScholarship
Two alcohols, three peaks eachEmpirical formula from % composition; distinguishing isomeric alcohols with equal ¹³C countsScholarship
Four bottles, four spectraIdentifying functional groups from IR descriptions and ¹³C countsBridge
Two isomers with three peaksDistinguishing a highly symmetric acid and ester (3 ¹³C peaks each) by IR, shifts, MS and titrationScholarship
Following a synthesis with spectroscopyFollowing a three-step synthesis by MS and ¹³C; Markovnikov; chirality; yieldScholarship
An aldehyde and a ketone that look alikeWhen MS and ¹³C counts fail to separate isomers, a chemical test decides; Tollens' stoichiometryScholarship
Three peaks for two chlorinesPredicting a two-chlorine isotope pattern by probability; identifying a dichloroalkaneScholarship
Dichloropropanes: telling the 2-peak isomers apartIsomer enumeration; ¹³C counts; chirality; hydrolysis products as confirmationScholarship
A fuming liquid and its three productsDeducing an acyl chloride and its acid, ester and amide products from a hydrolysis titration, chlorine isotope pattern, IR C=O positions and ¹³C countsScholarship
Selective hydrogenation: which bond was reduced?Deducing an unsaturated aldehyde and its three hydrogenation products from H2 uptake, Tollens' and bromine tests, IR and ¹³C shifts; geometric isomerism; yieldScholarship
Double bond or ring? Identifying four hydrocarbon gasesIdentifying C4H8 isomers (alkenes vs cycloalkanes) from molar mass, IR and ¹³C NMR, including a symmetric alkene with no C=C IR peakBridge
Itaconic acid: a fungal monomer and its hydrogenationIdentifying an unsaturated diacid from titration, IR, ¹³C NMR and MS; ruling out isomers through a hydrogenation product; symmetry and ¹³C counts; racemic product from hydrogenation; evaluating titration precisionScholarship
PHB bioplastic: what is the monomer?Identifying a hydroxy acid monomer from titration, composition, IR, ¹³C NMR, MS, oxidation and optical activity; polyester structure and chain length; comparing spectra of related compoundsScholarship
Counterfeit β-alanine in a sports supplementFive C3H7NO2 isomers with three ¹³C peaks each: formula from combustion data; distinguishing by shifts, fragments and optical activity; zwitterion bonding and melting points; evaluating a screening methodScholarship
Two bromobutanes and their twin peaksBromine isotope patterns (M, M+2; 1 : 2 : 1 for two Br), relative atomic mass from isotopes, fragment assignment, ¹³C environments and chirality to choose between C₄H₉Br isomersBridge
Dichlorobenzenes: symmetry, spectra and mothballsCounting 13C environments from symmetry in disubstituted benzene isomers; polarity vs boiling point; symmetry and packing vs melting point; yield calculation; evaluating purity from 13C spectraScholarship
The buttery flavour in ChardonnayIdentifying three related compounds from % composition, MS fragments, IR and ¹³C data; stereoisomerism including a meso form; volatility and hydrogen bondingScholarship
Mānuka honey: from nectar to methylglyoxalChoosing between five C₃H₆O₃ isomers from IR, ¹³C and optical activity; MS fragments of a dicarbonyl; intermolecular forces vs volatility; NaBH₄ reduction productsScholarship

Acids and bases · 46

Titration curve for ethanoic acid with sodium hydroxideWeak acid–strong base titration curve and buffersBridge
Seven solutions, seven pH valuespH of strong/weak acids, bases and salts; species concentrations; conductivityBridge
Designing an ammonia bufferBuffer pH, buffer preparation, response to added acidBridge
Methanoic acid from ant stingsKa from pH, mixing strong acid and base, dilution of weak vs strong acidsBridge
Titrating household ammonia with hydrochloric acidWeak base–strong acid titration curve; indicator choiceBridge
Ocean acidification and pāua shellsLinked equilibria, buffer ratio, saturation state, gas solubility and entropyScholarship
Glycine: an acid and a base in one moleculeZwitterions, species vs pH, buffer preparation, when the weak-acid approximation failsScholarship
Ranking weak acidsRanking acids by Ka, conjugate base strength, predicting acid–base reaction directionBridge
Making and testing an ethanoate bufferBuffer pH from masses; effect of added base and of dilutionBridge
From wine to vinegarOxidation of ethanol to ethanoic acid; ΔH; vinegar titration; weak acid pHScholarship
Orange streams: acid mine drainage on the West CoastRedox equations from descriptions, Fe(OH)3 precipitation pH, neutralisation quantityScholarship
Which antacid works best?Comparing antacids by neutralising capacity; dose calculation; side effectsScholarship
How indicators workIndicators as weak acid equilibria; colour from ratio; indicator choice; indicator errorScholarship
Is pH 6.6 acidic?Strong acid/base pH; Kw and temperature; meaning of neutralBridge
Ka from conductivity dataKa from percentage ionisation; strong vs weak acid comparisonsBridge
Acidic and basic saltspH of salt solutions; species concentrationsBridge
Which mixtures are buffers?Identifying buffer mixtures; buffer formed by partial neutralisationBridge
Blood's open buffer systemBicarbonate buffer ratio; closed vs open buffer systems; breathing as pH controlScholarship
Hydrochloric and methanoic acid: two curves, one titrantComparing strong-acid and weak-acid titration curves with the same base: key points, where the curves meet, indicator choiceScholarship
Phosphoric acid in cola and phosphate buffersPolyprotic acid pH (quadratic); choosing a buffer pair; buffer preparationScholarship
Sketching a titration curve for dimethylamineWeak base–strong acid titration curve: key points, sketch, buffering capacity, indicator choiceScholarship
Keeping the school pool safeSpecies fraction vs pH; disproportionation; dosing calculationScholarship
Identify the white crystalline acidMolar mass and Ka from one titration; pH at equivalence; indicator choiceScholarship
Designing a pH 5.00 bufferDesigning a buffer by partial neutralisation; testing capacityScholarship
Why aluminium chloride solution is acidicHydrated metal ions as weak acids; charge density; amphoteric hydroxideScholarship
Is the ethylamine really 70%?Weak base–strong acid titration: % w/w from titre, key points with the quadratic, steep range and indicator choice compared with ammonia, sources of error with a volatile analyteScholarship
Two acids in a dairy-shed cleanerMixture of a strong acid and a triprotic acid titrated with NaOH: two end points, concentrations of both acids, key points with common-ion suppression, indicators, why no third end point, effect of a misread end pointScholarship
Maleic acid for boat resins: a curve with two stepsDiprotic acid titration curve: key points at both equivalences, failure of the buffer approximation for a strong-ish first ionisation, end-point choice, cis/trans pKa comparisonScholarship
A borate buffer for a milk lipase assayBorate buffer: boric acid as a Lewis acid (shape change), preparation pH, pH after acid released by an enzyme, capacity to a pH limit and recipe redesignScholarship
A kiwifruit toner buffered with lactic acidLactate buffer: pH as made, after strong acid, after strong base and after dilution; capacity; acid strength from structureScholarship
Sulfite and hydrogencarbonate in the wineryAmphiprotic ions (HSO₃⁻, HCO₃⁻): Ka vs Kb, pH by ½(pKa1 + pKa2), K for a proton transfer with an escaping gas, pH of SO₃²⁻ and CO₃²⁻Scholarship
Chloroethanoic acids: from MCPA feedstock to near-strong acidAcid strength from structure (inductive effect, number, identity and position of halogens); weak-acid quadratic; K and position of an acid–base equilibrium; 'strong' vs highly dissociatedScholarship
Lidocaine: why the anaesthetic struggles in infected tissueFraction of an amine present as the free base at a given pH; pH-dependent solubility of an amine; maximum pH before precipitation; solubility of a salt vs its free baseScholarship
Citric acid kettle descaler: how acidic, and after dilution?Weak acid: concentration from mass, Ka and pKa from measured pH without the approximation, pH after dilution by quadratic, effect of dilution on pH and ionisationBridge
Nitrite and nitrous acid: which solution holds its pH?Deciding what each mixture contains after reaction, whether it resists pH change, and calculating pH (buffer, weak acid, weak base)Bridge
Lactic acid in silage juice: reading a pH-meter titrationEvaluating an experimental pH-meter titration curve: equivalence volume, pKa from data, buffering capacity from slopes, indicator choiceScholarship
Bread preservative: an acid and its salt titrated head to headTwo titration curves on one set of axes (acid with base, conjugate base with acid): key points, intersection pH, buffering capacity, end-point qualityScholarship
Propenoic acid in factory waste water: does dilution matter?Effect of dilution on a weak acid–strong base titration curve: key points with quadratics, limits of pH = pKa, buffering capacity, indicator choiceScholarship
Tris buffer for DNA work: prepared at 25 °C, used at 37 °CPreparing a Tris buffer by partial neutralisation; pH after adding acid; temperature dependence of pKa; capacity limits; comparing buffer systemsScholarship
Buffered oxide etch: an HF buffer in microchip makingHF/F⁻ buffer in buffered oxide etch: pH, stoichiometry of a reaction that consumes both buffer components, capacity, validity of assumptionsScholarship
Zinc oxide in nappy cream: a back titration with a hidden trapBack titration of zinc oxide in an ointment: concordant titres, % by mass, Ks-based choice of end-point pH, method validityScholarship
Diluting strong and weak acids and a strong basepH of strong and weak acids and bases before and after dilution; 5% test; degree of dissociation; water's contributionBridge
A washing booster with two end pointsTwo-stage titration curve of a carbonate/hydrogencarbonate mixture: composition, key points, buffering, indicators, CO2 lossScholarship
Is there hydrochloric acid in this vinegar?Titration curve of a strong + weak acid mixture (HCl-adulterated vinegar) with NaOH: key points, curve shape, hidden first end point, indicator evaluationScholarship
Three amino acids on an electrophoresis stripIsoelectric points of amino acids with ionisable side chains; species at a given pH; electrophoresis; buffer pH of a mixtureScholarship
The acidity of manuka honeyFree and lactone acidity of manuka honey by direct and back titration; weak-acid pH; when half-equivalence pH ≠ pKa; evaluating a Ka determinationScholarship

Solubility · 29

Magnesium hydroxide (milk of magnesia)Ks, common ion effect, Q vs Ks, dissolving in acidBridge
Silver chloride, silver chromate and the Mohr titrationComparing solubilities, selective precipitation, complex ionsBridge
Measuring Ks for calcium hydroxide (limewater)Determining Ks by titration; common ion; temperature effectBridge
Recovering zinc from galvanising waste waterSelective precipitation by pH, complex ions, amphoteric hydroxides, electrolytic recoveryScholarship
Tooth enamel, sugar and fluorideKs for a complex formula, acid attack on basic anions, maximum ion concentrationScholarship
'Golden rain': lead(II) iodideKs calculations, precipitation prediction, common ion, temperature effectBridge
Kidney stones: calcium oxalateKs, maximum ion concentration, complexation and pH effects on solubilityScholarship
The barium mealKs, solubility in g/L, common ion, why BaSO4 not BaCO3Bridge
Will calcium sulfate precipitate?Precipitation prediction after mixing; borderline Q vs KsBridge
Copper(II) and ammonia: from pale blue to deep bluePrecipitation then complex formation with ammonia; observations; pH of precipitationBridge
Working backwards: Ks from solubilityKs from solubility data; common ionBridge
Which salts dissolve in acid?Predicting the effect of acid on the solubility of different saltsBridge
Salty bore water: is the silver nitrate titration fit for purpose?Evaluating a precipitation titration: titre selection, Q vs Ks indicator logic, indicator concentration, pH constraintsScholarship
Hard water and kettle scaleTemporary vs permanent hardness; EDTA titration; softening by precipitationScholarship
Four sodium salts: justifying the anion testsIdentifying anions by precipitation tests; justifying each observation with Q vs Ks, acid-base removal of anions and complex formationScholarship
Why AgCl dissolves in ammonia but AgI does notCombining Ks and a formation constant; solubility in ammonia; halide identificationScholarship
Removing lead from industrial wastewaterChoosing a precipitant to meet a discharge limit; pH required; amphoterismScholarship
Fluoridating a city's water supplyUnit conversion; checking for unwanted precipitation; dosing at city scaleScholarship
Extracting gold at WaihiComplex formation making oxidation favourable; reagent mass; pH control of HCNScholarship
Separating iron from magnesium by pHpH window for separating metal ions as hydroxides; 'complete' precipitation criterionScholarship
Iodine from gas-field brine: can silver separate iodide from chloride?Selective precipitation of iodide from chloride-rich brine with silver ions: onset, % criterion, why dilution cannot help, yield, redox alternativeScholarship
Zinc in roof run-off: why too much lime redissolves itAmphoteric Zn(OH)2: dissolving by zincate complex formation, total solubility vs pH, minimum-solubility pH, treatment windowScholarship
Silver sulfate: Ks from an evaporation, then the common-ion effectKs from an experimental solubility; common-ion effect with a non-negligible change; comparing common ionsBridge
Wine diamonds: Ks of potassium hydrogentartrateKs of potassium hydrogentartrate by acid–base titration of the saturated solution; concordant titres; common ion; speciation at wine pH; Q vs Ks for cold stabilisation; evaluationScholarship
Recovering copper from a plating rinseSelective precipitation of Cu(OH)2 before Zn(OH)2 by pH control: onset pH values, % removal criterion, product mass, zinc discharge limit and amphoterism, evaluationScholarship
Leaching nickel with ammoniaAmmonia leaching of nickel: Ni(OH)2 dissolving as [Ni(NH3)6]2+, combined K, free metal ion, Q vs Ks with a complex, precipitation on ammonia strippingScholarship
Copper in Marlborough vineyard soilspH dependence of Cu(OH)2 solubility in vineyard soils; liming; Bordeaux mixture stoichiometry; evaluating a Ks-only modelScholarship
The mislabelled bottle: which cation is it?Identifying an unknown cation from concentration-dependent precipitation tests: Q vs Ks, ruling out alternatives, extent of precipitation, reliabilityScholarship
Silver carbonate: Ks, solubility and common ionsKs expression for an A2B salt, solubility in mol L-1 and g L-1, common-ion effect from each ion, effect of anion hydrolysisBridge

Equilibrium and rates · 30

Cobalt complexes and hydrogen iodideKc, Q, Le Chatelier with observations, collision theoryBridge
The Haber process: yield versus rateIndustrial equilibrium: yield vs rate, Kc, temperature dependence of KBridge
Marble chips and acid: following a reactionRates from gas volume data; limiting reagent; collision theoryBridge
Brown haze over Auckland: nitrogen oxidesKc, response to compression with observations, quadratic for new equilibrium, kinetics of NO formationScholarship
Pushing an esterification to completionKc for esterification, yield with excess reactant via quadratic, role of catalystScholarship
Carbon monoxide poisoning and hyperbaric oxygenCompetitive equilibrium; K expression with given data; Le Chatelier in treatmentScholarship
Making sulfuric acid: the Contact processKc by ICE table; ΔH; entropy and temperature; industrial conditionsScholarship
The iron(III) thiocyanate equilibriumKc calculation; colour changes with Le Chatelier including complexation and temperatureBridge
Which way will it go?Q vs K to predict direction; equilibrium amounts from KcBridge
The disappearing crossRate from 1/t; collision theory for concentration and temperatureBridge
The Haber process: what happens when you squeeze it?Kc; quantitative effect of a volume change on Q; compromise conditionsScholarship
Hydrogen iodide: one equilibrium, three K valuesManipulating K for reversed and scaled equations; ICE with square rootScholarship
Yellow to orange: chromate and dichromatepH-dependent equilibrium with large K; competing precipitationScholarship
Pink to blue: cobalt complexesComplex-ion equilibrium; ratio depends on [Cl⁻]⁴; Le Chatelier with AgNO₃ and temperatureScholarship
Ammonia in streams: why pH matters for fishFraction of a conjugate pair vs pH; temperature effect on K; environmental applicationScholarship
How much PCl5 falls apart?Quadratic ICE for a dissociation; percentage dissociation; effects of adding product, pressure and temperatureScholarship
Why soft drinks go flatGas solubility equilibrium; pH from dissolved CO₂; temperature and pressure effectsScholarship
Inside a catalytic converterThermodynamically favourable but slow reactions; heterogeneous catalysis; ΔH; stoichiometryScholarship
Why museum chalcanthite crumblesHeterogeneous equilibrium CuSO4·5H2O ⇌ CuSO4·3H2O + 2H2O(g): Kc from a mass loss, Q vs Kc at different humidities, Le Chatelier with colour observations, evaluating the measurementScholarship
Silver that comes and goesHeterogeneous redox equilibrium Ag+ + Fe2+ ⇌ Ag + Fe3+: Kc from a thiocyanate titration, Q vs Kc, Le Chatelier with observations, link to E°cellScholarship
Racing the iodine clockIodine clock: average rate from a clock time, effect of concentration, temperature and catalyst explained by collision theoryBridge
Why bromine water slowly loses its colourKc for a heterogeneous-solvent equilibrium from pH data; Q after dilution; colour changes on removing H⁺, adding acid and precipitating bromideBridge
Breaking down peroxide from salmon-farm bathsGas-volume rate data: disproportionation, concentration from final volume, average rate, anomalous reading, constant half-life, collision theory predictions, temperature rise from ΔfHScholarship
Nail-polish-remover ester and water: measuring KcKc for ester hydrolysis from initial amounts and titration data with a catalyst blank; choosing replicate results; justifying method features; effect of extra water; cancelling volumesScholarship
The Mond process: one reaction, two directionsKc with units for a heterogeneous equilibrium from experimental data; Q vs Kc to predict deposition; observations of pressure and solids; ΔH and ΔS(system) from data; ΔS(surroundings) = −ΔH/T; ΔS(total) and crossover temperature; linking spontaneity to equilibrium position, pressure and rateScholarship
Recycling waste HCl into chlorine: the Deacon equilibriumKc with units from equilibrium amounts; Q vs Kc; colour observations on compression and heating; ΔrH from ΔfH; evaluating a catalyst change in terms of position and rateScholarship
Why a copper etchant changes colourCopper(II) chloro-complex equilibrium: Kc from colorimetric data, Q after dilution (fourth-power term), colour predictions for several changes, sign of ΔH from Kc at two temperatures, evaluating a misconception about waterScholarship
Oxygen weed in a tube: an indicator equilibriumIndicator equilibrium: Kc expression and value, ratio of coloured forms at different [H⁺], Le Chatelier with colour observations in a photosynthesis experimentBridge
Why more iodine takes longer to disappearClock-type initial rates: rate from [I₂]₀/t, orders by inspection, rate constant, zero order and the rate-determining step, validity of the method, temperature effectScholarship
Measuring Kc for the triiodide ion by partitionTriiodide equilibrium measured by partition between hexane and aqueous KI: colour observations, Kc from titration and distribution data, Le Chatelier in two phases, evaluating assumptionsScholarship

Redox and electrochemistry · 35

A zinc–silver cell and dichromate oxidationsGalvanic cells, E°cell, salt bridges, balancing redox equationsBridge
Electrolysis of molten salt and brineElectrolysis of molten and aqueous NaCl; minimum voltageBridge
How much iron is in an iron supplement?Redox titration: iron in tablets; choice of acid; air oxidationBridge
Rust, galvanising and sacrificial anodesCorrosion, sacrificial protection, galvanising vs tin platingBridge
Vitamin C in kiwifruitIodometric back titration; redox equations from descriptions; validityScholarship
Fuel cells versus car batteriesFuel cell and lead–acid half-equations, electrical energy and efficiency, entropy limitScholarship
Oxidation numbers and balancing redox equationsOxidation numbers; balancing redox in acid; disproportionationBridge
Cleaning tarnished silver with aluminium foilElectrochemical tarnish removal; E°cell; reacting masses; role of electrolyteScholarship
Is there enough oxygen for trout?Multi-step redox analysis (Winkler method); mole ratios through a chain; gas solubilityScholarship
Ranking metals with cell potentialsE°cell for several cells; predicting displacement; cell notationBridge
Electrolysing copper sulfate two waysElectrolysis of CuSO4 with inert vs copper electrodes; minimum voltageBridge
Two cells, two voltmeter readingsGalvanic cells: deriving E° from measured voltages, electrode observations, salt-bridge ion movement, predicting reactionsScholarship
Protecting the Interislander's hullCorrosion half-equations; sacrificial anodes; mass consumed from currentScholarship
How far can each metal reduce dichromate?Predicting how far a reductant takes a multi-step reduction from E° values; observations; balancing; reacting mass; thermodynamic vs kinetic argumentsScholarship
Copper and chrome platingFaraday calculations for plating; electrons per atom; why some metals can't be plated from waterScholarship
Standardising permanganate with oxalatePermanganate–oxalate titration; balancing; autocatalysisBridge
Which halogen displaces which?Halogen displacement predicted with E°; observations in a non-polar layerBridge
The hydrogen fuel cellHydrogen fuel cell half-equations; E°; charge to moles of H₂Bridge
Oxidation numbers in organic chemistryOxidation numbers of carbon in organic oxidation; electrons per stepBridge
An iron–copper cell: what you would seeGalvanic cell: half-equations, electron flow, E°cell, electrode and solution observations, salt-bridge ion movement, linked massesBridge
How much copper is in brass?Iodometric analysis of copper; precipitation driving an unfavourable redox reactionScholarship
Tiwai Point aluminium smelterElectrolysis of molten alumina; Faraday calculations at industrial scale; anode consumptionScholarship
Air-activated hand warmersRusting as an electrochemical process; role of electrolyte; energy per gramScholarship
Recovering silver from silver chloride wasteE° for a metal/insoluble-salt couple; recovery stoichiometry; effect of insolubility on E°Scholarship
Roadside breath testingFuel-cell breath tester: half-equations; charge to moles; comparison with legal limitScholarship
Permanganate in acid and in neutral solutionPermanganate reduction products depend on pH; oxidation states and colours; reacting massesScholarship
Inside a pH probe: the silver/silver chloride electrodeDeriving E° of metal/insoluble-salt electrodes from cell voltages; observations including electrodes that gain mass; salt-bridge ion movement; Faraday calculation; linking E° to Ks; evaluating a reference electrodeScholarship
Cerium(IV): a titrant that rivals permanganateDeriving E° of an ion/ion couple from cell voltages with platinum electrodes; observations and salt-bridge movement; feasibility predictions with E°cell; redox titration with concordant titres; evaluating a titrantScholarship
Four oxidation states, four colours: vanadium redox storageOxidation numbers and half-equations for V(II)–V(V); E°cell for a flow battery; colour changes on charge and discharge; comproportionation on crossover; charge and energy stored; competing reactions at electrodes and kinetic controlScholarship
Electrolysing potassium iodide: iodine without seaweedElectrolysis of aqueous potassium iodide: species present, competing half-reactions ranked by E°, observations with indicator, minimum voltage, Faraday calculations, comparison with KFScholarship
A zinc–bromine flow battery: potentials, charging and self-dischargeDeriving E° for non-metal and ion/ion couples from measured voltages; observations and ion movement in a cell with inert electrodes; Faraday quantities on charging; evaluating self-discharge in a flow batteryScholarship
Ferrate(VI): iron from +6 down to 0Iron in oxidation states +6, +3, +2 and 0: ferrate decomposition in acid, how far different reductants reduce iron(III), competing reduction of H+, back titration for purity, evaluation of the methodScholarship
Lead and silver: which ions can carry the charge?Galvanic cell half-equations and E°cell; choosing a salt bridge using precipitation chemistry; observations; Faraday calculations; evaluating a yield; cell voltage as the reaction approaches equilibriumScholarship
Iodine from Chilean caliche: stopping at the right oxidation stateOxidation numbers of iodine species; predicting how far each reductant reduces iodate from E° values; colour observations with starch; reacting quantities for a two-stage industrial reduction; a species acting as both oxidant and reductantScholarship
Pinning down E° for cobalt: two cells, one unknownDeriving an unknown E° from measured cell voltages and cross-checking it; electrode and colour observations; salt-bridge ion movement; Faraday calculations; evaluating non-standard measurements; predictions from the derived E°Scholarship

Quantitative chemistry · 30

Water of crystallisation in washing sodaTitration to find water of crystallisation; errors and validityBridge
How much calcium carbonate is in an eggshell?Back titration, percentage purity, sources of errorBridge
Hokey pokey and impure baking sodaTwo independent analyses of a mixture; thermal decomposition energetics and entropyScholarship
Making a standard solution and standardising acidPreparing standard solutions, dilution, standardising an acidBridge
What went wrong with the titration?Effects of procedural errors on titration results; uncertaintyBridge
How much nitrogen is in this fertiliser?Back titration for ammonium; percentage N and purity; sources of errorScholarship
How much water is in blue copper sulfate?Water of crystallisation by heating; error analysisBridge
Two end points in one titrationDouble-indicator titration of a carbonate/hydrogencarbonate mixtureBridge
Magnesium and hydrochloric acidLimiting reagent, gas volume, pH of excess acidBridge
Parts per million in drinking waterppm and mg/L conversions; preparing dilute standardsBridge
Two students standardise sodium hydroxideProcessing raw titration data from two students; precision vs accuracy; diagnosing systematic and random errorsScholarship
Does the vitamin C tablet contain what it claims?Iodine titration of ascorbic acid; scaling; label claim; sources of errorScholarship
A fishy-smelling amineCombustion analysis with N by difference; amine isomers; ¹³C identification; basicityScholarship
Formulae from massesEmpirical formula from % composition and reacting massesBridge
Sulfate in fertiliser by gravimetric analysisGravimetric analysis of sulfate; percentage compositionBridge
Identifying a diprotic acidMolar mass of a diprotic acid by titration; ¹³C confirmation; two-stage titration curveScholarship
Checking the alcohol content of a Marlborough wineRedox back titration through three stoichiometric steps; % alcohol by volumeScholarship
Which carbonate is it?Identifying a metal carbonate from CO₂ mass loss; uncertainty; systematic errorScholarship
Aspirin analysis: the hydrolysis methodBack titration after ester hydrolysis; 2 : 1 stoichiometry; comparison with direct titrationScholarship
How strong is hair bleach?Permanganate titration of H₂O₂; concentration in g L⁻¹; 'volume strength'Scholarship
Is this tanker of milk too sour?Raw titration data: concordant titres, standardising NaOH with sulfamic acid, titratable acidity of milk, uncertainty, error direction, validityScholarship
Is the farm lime worth the price?Standardising HCl with borax; back titration of agricultural lime; effloresced primary standard; dolomite and dissolved CO2 as threats to accuracy and validityScholarship
Nitrite in a bacon-curing concentrateStandardising KMnO4 with ammonium iron(II) sulfate; nitrite by reverse titration; equations from descriptions; interferences and error directionScholarship
The iodine value of avocado oilIodometry with a blank: iodine value of an oil (ICl addition to C=C), thiosulfate standardised with dichromate, average C=C per triglyceride, method evaluationScholarship
Causmag for grass staggers: is the label honest?Back titration from raw titre data: choosing concordant titres, % purity, indicator choice justified by Q vs Ks, validity vs accuracy, direction of errorsScholarship
Green vitriol for iron-gall ink: two methods, two answersWater of crystallisation by redox titration and by gravimetric analysis; concordant titres; evaluating disagreeing methods; direction of systematic errorsScholarship
Titratable acidity of Marlborough grape juiceStandardising NaOH against a primary standard with unequal masses, titratable acidity of a diprotic acid, end-point choice, validity of a reporting convention, direction of errorsScholarship
How strong is the drain cleaner?Choosing concordant titres, dilution factor, mol L⁻¹ and g L⁻¹, direction of procedural errorsBridge
Citric acid in a lime-juice cordialRaw burette readings for a triprotic acid: titre selection, dilution and 1 : 3 mole ratio, indicator choice from pKa values, validity vs accuracy, direction of errorsScholarship
Sulfur dioxide in dried apricotsIodine titration of a food preservative: titre selection, blank correction, spike recovery, compliance judgement and direction of errorsScholarship