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.
350 problems · 20 free to try now
Free problems
- Phosphorus chlorides: molecules and ionsBridge
- Three ways to find the enthalpy of combustion of ethanolBridge
- From propene to an esterBridge
- Identifying an ester, C4H8O2Bridge
- Titration curve for ethanoic acid with sodium hydroxideBridge
- Magnesium hydroxide (milk of magnesia)Bridge
- Cobalt complexes and hydrogen iodideBridge
- A zinc–silver cell and dichromate oxidationsBridge
- Water of crystallisation in washing sodaBridge
- Hokey pokey and impure baking sodaScholarship
- Vitamin C in kiwifruitScholarship
- Ocean acidification and pāua shellsScholarship
- A fruity ester that rotates lightScholarship
- Calcium chloride on icy roadsScholarship
- Methanol as a liquid carrier for hydrogenScholarship
- Recovering zinc from galvanising waste waterScholarship
- From soot-free combustion to a structureScholarship
- The 'inert' gas that isn't: xenon compoundsScholarship
- How efficient is a camping stove?Scholarship
- Brown haze over Auckland: nitrogen oxidesScholarship
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Particles, bonding and structure · 16
- 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
- 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
- Shapes of polyatomic ionsLewis structures and shapes of polyatomic ionsBridge
- 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
- 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
- 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
- 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 · 12
- 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
- Hydrogenating etheneΔH by bond enthalpy and ΔfH; energy diagrams; catalystsBridge
- Will it happen by itself?Predicting entropy changes and spontaneity from ΔH and ΔSBridge
- Cold packs and potassium nitrateΔH of solution by calorimetry; link to solubility and entropyBridge
- 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
- 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
- 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 · 21
- 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
- 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
- Up or down the oxidation ladderChoosing NaBH4 or acidified dichromate; oxidation vs reduction; reflux vs distillation; percentage yieldBridge
- 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
- 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
- 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
Spectroscopy · 12
- 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
- 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
- Four bottles, four spectraIdentifying functional groups from IR descriptions and ¹³C countsBridge
- 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
- 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
Acids and bases · 14
- 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
- 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
- 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
- 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
- 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
Solubility · 11
- 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
- 'Golden rain': lead(II) iodideKs calculations, precipitation prediction, common ion, temperature effectBridge
- 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
- 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
- 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 · 9
- 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
- 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
- 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
- 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
Redox and electrochemistry · 12
- 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
- Oxidation numbers and balancing redox equationsOxidation numbers; balancing redox in acid; disproportionationBridge
- 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
- 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
Quantitative chemistry · 11
- 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
- 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 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
- Formulae from massesEmpirical formula from % composition and reacting massesBridge
- Sulfate in fertiliser by gravimetric analysisGravimetric analysis of sulfate; percentage compositionBridge
- How strong is the drain cleaner?Choosing concordant titres, dilution factor, mol L⁻¹ and g L⁻¹, direction of procedural errorsBridge