Key term
WJEC AS-Level Chemistry 1410QS
Formulae and Equations
Basic Ideas About Atoms
Topic overviewRadioactive decay and nuclear equationsAlpha, beta and gamma radiationHalf-life, dating and the uses of radioisotopes: half-life of radioactive decayHalf-life, dating and the uses of radioisotopes: adverse consequences for living cellsIonisation energies and electronic structureOrbitals and the filling of sub-shellsAtomic spectra and the energy of light: atomic emission spectrum of the hydrogen atomAtomic spectra and the energy of light: relationship between energy and frequencyAtomic spectra and the energy of light: significance of the frequency
Chemical Calculations
Topic overviewRelative masses and the mass spectrometer: relative atomicRelative masses and the mass spectrometer: how a mass spectrometer worksRelative masses and the mass spectrometer: molecular ionThe mole, the Avogadro constant and molar mass: relative mass terms and simple mass spectraThe mole, the Avogadro constant and molar mass: moles and percentage composition by massEmpirical and molecular formulaeConcentration, solubility and titration calculations: concentration in mol dm-3 and in g dm-3Concentration, solubility and titration calculations: stoichiometry and the limiting reagentConcentration, solubility and titration calculations: titration calculations and estimating a titreGas volumes and the ideal gas equationYield, atom economy and experimental uncertainty: concepts of atom economy and percentage yieldYield, atom economy and experimental uncertainty: how to estimate the percentage error
Bonding
Topic overviewIonic bonds and covalent bonds: ionic bonding in terms of ion formationIonic bonds and covalent bonds: covalent bonding and forcesElectronegativity, polarity and in-between bonds: concepts of electronegativity and bond polarityElectronegativity, polarity and in-between bonds: forcesForces between moleculesHydrogen bondingShapes of molecules and ions: VSEPR principle and its useShapes of molecules and ions: bond angles associated with linear
Solid Structures
The Periodic Table
Topic overviewHow the Periodic Table is organisedOxidation and reduction as electron transferTrends across periods and down groupsGroup 2: reactions, trends and the reasons behind them — reactions with oxygen, water and dilute acidGroup 2: reactions, trends and the reasons behind them — trends down the groupGroup 2: reactions, trends and the reasons behind them — thermal stability of the carbonatesGroup 2: reactions, trends and the reasons behind them — oxides and hydroxidesIdentifying ions, making salts and gravimetric analysis: identifying cations with sodium hydroxideIdentifying ions, making salts and gravimetric analysis: preparing a soluble salt from an acidGroup 7: the halogens — physical properties and the trend in volatilityGroup 7: the halogens — reactions of the halogens with metalsGroup 7: the halogens — displacement reactions and the trendGroup 7: the halogens — halide ions as reducing agents, uses of chlorine and the chlorate equilibrium
Simple Equilibria and Acid-Base Reactions
Thermochemistry
Rates of Reaction
The Wider Impact of Chemistry
Organic Compounds
Hydrocarbons
Topic overviewAlkane bonding, combustion and fossil fuels: combustion reaction of alkanes and benefitsAlkane bonding, combustion and fossil fuels: combustion calculations and acid rainRadical substitution of alkanesThe C=C bond and why alkenes are reactiveE–Z isomerism in alkenesElectrophilic addition, Markovnikov's rule and testing for alkenes: mechanism of electrophilic additionElectrophilic addition, Markovnikov's rule and testing for alkenes: Markovnikov's rule and the bromine water testElectrophilic addition, Markovnikov's rule and testing for alkenes: testing for a C=C bondHydrogenation and addition polymers: conditions requiredHydrogenation and addition polymers: nature of addition polymerisation
Halogenoalkanes
Topic overviewNucleophilic substitution by hydroxide ionsElimination to form alkenesReactivity of the carbon–halogen bond and the silver nitrate testUses of halogenoalkanes, CFCs and the ozone layer: uses of halogenoalkanes and CFCsUses of halogenoalkanes, CFCs and the ozone layer: radical mechanismUses of halogenoalkanes, CFCs and the ozone layer: replacements for CFCsHeating under reflux in the laboratory
Alcohols and Carboxylic Acids
Topic overviewTwo routes to ethanol: hydration and fermentation — hydration of etheneTwo routes to ethanol: hydration and fermentation — fermentationTwo routes to ethanol: hydration and fermentation — comparing the two routes on rateClassifying alcohols and dehydrating themOxidising alcohols to aldehydes, ketones and acidsChemical tests for alcohols and carboxylic acidsCarboxylic acids, bases and saltsMaking an ester and separating it by distillation: esterificationMaking an ester and separating it by distillation: carrying out the preparationMaking an ester and separating it by distillation: separating and purifyingMaking an ester and separating it by distillation: yield
Instrumental Analysis
Practical Skills and Techniques
Topic overviewMeasuring mass, volume, time and temperatureStandard solutions and titration techniqueIndicators and acid–base titration curvesHeating, refluxing, distilling and purifying: HeatingHeating, refluxing, distilling and purifying: purifyingMelting temperature, chromatography and pH measurementElectrochemical cells, rate methods and working safely: Electrochemical cellsElectrochemical cells, rate methods and working safely: rate methods and working safely
Planning, Analysis and Evaluation
Core Experiments and Their Chemistry
Topic overviewGravimetric and acid–base analysisEnthalpy and rate experiments: EnthalpyEnthalpy and rate experiments: rate experimentsRedox titrations and electrochemical cellsEquilibrium constants and following a titration with a pH probeOrganic synthesis, separation and identification: Organic synthesisOrganic synthesis, separation and identification: identification tests and chromatography
Mathematical Skills in Chemistry
Topic overviewUnits, standard form and proportion in chemical calculation: volume, equilibrium, rate and energy unitsUnits, standard form and proportion in chemical calculation: standard formUnits, standard form and proportion in chemical calculation: proportionUnits, standard form and proportion in chemical calculation: checking answers, buffers, rate constants and unitsSignificant figures, means and uncertainty in experimental data: significant figures in multiplicationSignificant figures, means and uncertainty in experimental data: relative atomic mass as a weighted meanSignificant figures, means and uncertainty in experimental data: absolute and percentage uncertaintySymbols, rearranging equations and logarithms: chemical symbols and what each one assertsSymbols, rearranging equations and logarithms: rearranging an equationSymbols, rearranging equations and logarithms: substituting into equations for Kc, enthalpy and pHSymbols, rearranging equations and logarithms: logarithms, the Arrhenius equation and rearranging formulaeGraphs: plotting, gradients, intercepts and tangents — reading a spectrumGraphs: plotting, gradients, intercepts and tangents — reaction order from data and plotting good graphsGraphs: plotting, gradients, intercepts and tangents — Arrhenius plots, zero-order graphs and tangentsGraphs: plotting, gradients, intercepts and tangents — initial rates from tangents and interpreting graphsShape, symmetry and three-dimensional structure: ShapeShape, symmetry and three-dimensional structure: symmetry
Core Experiments and Their Chemistry
- 7 subtopics
- 16 things to know
- All units
What Core Experiments and Their Chemistry covers
Core Experiments and Their Chemistry is assessed throughout WJEC Chemistry and in the unit 5 practical examination rather than in one unit of its own. 101 recall questions across 7 subtopics.
Where it is assessed
All units
Skills assessed throughout, and in the unit 5 practical examination.
Check the WJEC specification ↗The 7 subtopics
Each one has its own page. WJEC AS Chemistry students sit this topic in the first year.
- Gravimetric and acid–base analysisRecall questions on Gravimetric analysis and acid–base analysis.Open →
- Enthalpy and rate experiments: EnthalpyTen recall questions on enthalpy and rate experiments: Enthalpy.Open →
- Enthalpy and rate experiments: rate experimentsEleven recall questions on enthalpy and rate experiments: rate experiments.Open →
- Redox titrations and electrochemical cellsRecall questions on Redox titrations and electrochemical cells.Open →
- Equilibrium constants and following a titration with a pH probeSixteen recall questions on equilibrium constants and following a titration with a pH probe.Open →
- Organic synthesis, separation and identification: Organic synthesisFifteen recall questions on organic synthesis, separation and identification: Organic synthesis.Open →
- Organic synthesis, separation and identification: identification tests and chromatographyDistinguishing aldehydes from ketones, the triiodomethane test for CH₃CO– and CH₃CH(OH)– groups, and separating and identifying amino acids by one- and two-way paper chromatography.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Evaluation
Why might a gravimetric determination of water of crystallisation give a value that is too low?
Key term
Why is the solution acidified with dilute hydrochloric acid before barium chloride is added in a gravimetric sulfate determination?
Evaluation
Why is an anhydrous salt weighed quickly and transferred immediately when its enthalpy change of solution is measured?
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Why is starch added to an iodine clock mixture, and why does the colour appear suddenly rather than gradually?
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Why is a thermostatic water bath essential in an investigation of how rate depends on concentration?
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Why is no indicator needed in a titration of iron(II) ions with potassium manganate(VII)?
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Why is dilute sulfuric acid, rather than hydrochloric or nitric acid, used to acidify a manganate(VII) titration?
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Suggest why a measured cell potential falls slowly during a long measurement.
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Why is the equivalence point of the titration of ethanoic acid with sodium hydroxide above pH 7?
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Why must the pH probe be kept fully immersed and the solution stirred throughout a pH titration?
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Why is ethanol used as the solvent when the hydrolysis rates of halogenoalkanes are compared using aqueous silver nitrate?
Evaluation
Why does the order of rates in the hydrolysis of halogenoalkanes follow the carbon–halogen bond strengths?
Evaluation
Why is a water bath, rather than a naked flame, used for the hydrolysis of a halogenoalkane?
Key term
How would you show that an unknown liquid contains a hydroxyl group?
Key term
Why must an equilibrium mixture be kept at a constant temperature while it stands before analysis?
Take Core Experiments and Their Chemistry further
The same content, four other ways.
Questions from this topic
Each one with the model answer underneath.
- 1
Describe how the formula of a hydrated salt can be found by heating it in a crucible.
Model answer
Weigh a clean dry crucible and lid, add the hydrated salt and reweigh, then heat gently, allow the crucible to cool in a desiccator and reweigh. Repeat the heating and weighing until two successive masses agree, and use the loss in mass as the mass of water driven off.
- 2
Why is a sample heated to constant mass in a gravimetric determination?
Model answer
Constant mass shows that no further water or gas is being lost, so the decomposition or dehydration is complete. Stopping after one heating risks leaving some water behind and underestimating the amount of water of crystallisation.
- 3
Why is the crucible cooled in a desiccator rather than in the open laboratory?
Model answer
A hot crucible must be cooled before weighing because warm air currents affect the balance, and an anhydrous salt readily reabsorbs moisture from the air. A desiccator provides a dry atmosphere so that the mass recorded is that of the anhydrous solid.
- 4
Heating 2.50 g of hydrated copper(II) sulfate leaves 1.60 g of the anhydrous salt. Determine the number of molecules of water of crystallisation per formula unit. (Mr of CuSO₄ = 159.6, Mr of H₂O = 18.0)
Model answer
Mass of water lost = 2.50 − 1.60 = 0.90 g, so moles of water = 0.90 / 18.0 = 0.0500 mol. Moles of CuSO₄ = 1.60 / 159.6 = 0.01003 mol. The ratio of water to salt is 0.0500 / 0.01003 = 4.99, so the formula is CuSO₄·5H₂O.
- 5
Why might a gravimetric determination of water of crystallisation give a value that is too low?
Model answer
Heating may have been insufficient, so some water remained in the solid, which makes the measured mass loss too small. The anhydrous solid may also have absorbed moisture from the air before it was reweighed, which has the same effect.
- 6
Why can heating a hydrated salt too strongly give a result that is too high?
Model answer
Overheating can decompose the anhydrous salt itself, driving off further products such as sulfur trioxide or oxygen. The extra mass lost is then wrongly counted as water of crystallisation.
What is inside Levo
Six ways to work the same material.
Core Experiments and Their Chemistry revision questions
- Is Core Experiments and Their Chemistry examined at AS in WJEC Chemistry?
- Yes. It sits in All units, which you take in the first year, so it is on the AS paper as well as counting towards the full A level.
- What does Core Experiments and Their Chemistry cover in WJEC AS-Level Chemistry?
- 7 subtopics: gravimetric and acid–base analysis, enthalpy and rate experiments: enthalpy, enthalpy and rate experiments: rate experiments, redox titrations and electrochemical cells, equilibrium constants and following a titration with a ph probe, organic synthesis, separation and identification: organic synthesis and organic synthesis, separation and identification: identification tests and chromatography. Each one has its own page with questions and model answers.
- How is Core Experiments and Their Chemistry organised?
- By the WJEC 1410QS specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Core Experiments and Their Chemistry, on a schedule.
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