Key term
OCR GCSE Chemistry A J248
Chemical Reactions
Topic overviewWriting formulae of elements and compoundsBalanced equations, and deducing formulae from ionsIonic equations, and state symbolsThe mole and the Avogadro constantConservation of mass, and changes of mass in open systemsStoichiometry, and calculating reacting massesExothermic and endothermic reactions, and reaction profilesActivation energy, and bond energy calculationsOxidation and reduction, by oxygen and by electronsAcids, alkalis and neutralisationThe ionic equation for neutralisation, and reactions of acidsDilute and concentrated, weak and strongThe pH scale, and hydrogen ion concentrationpH as a factor of ten, and measuring pHProducts at the electrodes, and molten ionic compoundsElectrolysis of aqueous solutionsInert and non-inert electrodes
Elements, Compounds and Mixtures
Topic overviewPurity, and melting point dataRelative formula mass and empirical formulaeFormulations, and separating mixturesPaper and thin layer chromatographyInterpreting chromatograms and Rf valuesChoosing a purification methodMetals and non-metals in the Periodic TableElectron arrangement and position in the Periodic TableIonic, covalent and metallic bonding comparedDot and cross diagrams, and the limits of modelsReactions, electron arrangement and Mendeleev's tableCarbon's four bonds, and the variety of organic compoundsDiamond, graphite, fullerenes and grapheneBond strength, intermolecular forces and predicting stateBulk properties of ionic, molecular and giant structuresNanoparticles: size and surface area to volumeUses and risks of nanoparticulate materials
Global Challenges
Topic overviewExtracting metals by reduction and by electrolysisBiological methods of metal extractionRate against yield in industry, and reaction conditionsThe Haber process and fertiliser productionNitrogen, phosphorus and potassium in agricultureLife cycle assessmentRecycling, and the decisions behind itAlloys, and the corrosion of metalsComparing glass, ceramics, polymers, composites and metalsFunctional groups and homologous seriesPredicting the products of organic reactionsAddition polymerisationCondensation polymerisation, and making a polymerDNA and other natural polymersFractional distillation of crude oilThe fractions, and crude oil as a feedstockDependence on hydrocarbons, and crackingChemical cells and fuel cellsThe Earth's early atmosphere, and how oxygen developedThe greenhouse effect, and evidence for climate changeEffects of carbon dioxide and methane, and air pollutantsProducing potable water
Monitoring and Controlling Chemical Reactions
Topic overviewConcentration in mol/dm³, and titrationTitration calculations, and the mass of a soluteMolar gas volume and the volumes of gasesTheoretical mass and percentage yieldAtom economy, and choosing a reaction pathwayMeasuring the rate of a reaction, and rate graphsFactors affecting rate, and collision theorySurface area and rateCatalysts and how they workReversible reactions and dynamic equilibriumChanging the conditions of an equilibriumActivation energy, and enzymes as catalysts
Particles
Predicting and Identifying Reactions
Topic overviewGroups 1, 7 and 0, and why they behave as they doTransition metalsPredicting reactivity from the Periodic TableReactivity of metals with water and acidsTests for oxygen, hydrogen, carbon dioxide and chlorineTests for aqueous cations and anionsFlame tests, and identifying metal ionsIdentifying a species from test resultsInstrumental methods of analysis
Monitoring and Controlling Chemical Reactions
Molar gas volume and the volumes of gases
- 3 things to know
- Paper 4
Overview
The 24 dm³ molar gas volume at room temperature and pressure, why every gas occupies the same volume, converting between moles and volume, and calculating gas volumes from reacting masses and equations.
What you need to know
Answer each one before you reveal it.
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Numbers
How do you calculate the number of moles of a gas from its volume in dm³ at room temperature and pressure?
Numbers
How do you calculate the volume of a gas at room temperature and pressure from the number of moles?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What volume is occupied by one mole of any gas at room temperature and pressure?
Model answer
24 dm³.
- 2
Express the volume of one mole of gas at room temperature and pressure in cm³.
Model answer
24 000 cm³.
- 3
Explain why one mole of any gas occupies the same volume as one mole of any other gas under the same conditions.
Model answer
The volume of a gas depends on the number of particles and the large spaces between them, not on the size or mass of the individual particles.
- 4
How do you calculate the number of moles of a gas from its volume in dm³ at room temperature and pressure?
Model answer
Divide the volume in dm³ by 24.
- 5
How do you calculate the volume of a gas at room temperature and pressure from the number of moles?
Model answer
Multiply the number of moles by 24 to give the volume in dm³.
- 6
Calculate the volume occupied by 3.0 mol of carbon dioxide at room temperature and pressure.
Model answer
3.0 × 24 = 72 dm³, given to 2 significant figures.
Other ways to work this
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