Key term
OCR GCSE Chemistry A J248
Chemical Reactions
Topic overviewWriting formulae of elements and compoundsBalanced equations, and deducing formulae from ionsState symbols in equationsConservation of mass, and changes of mass in open systemsExothermic and endothermic reactions, and reaction profilesActivation energy and why reactions need itOxidation and reduction in terms of oxygenAcids, alkalis and neutralisationThe ionic equation for neutralisation, and reactions of acidsThe pH scale, acidity and alkalinityMeasuring pH with indicators and pH metersProducts 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 electrolysisThe 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 polymerisationDNA 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 overviewCarrying out an acid–alkali titrationTheoretical mass and percentage yieldAtom economy and its calculationMeasuring the rate of a reaction, and rate graphsFactors affecting rate, and collision theorySurface area and rateCatalysts and how they workReversible reactions and dynamic 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
Global Challenges
Comparing glass, ceramics, polymers, composites and metals
- 3 things to know
- Paper 2
Overview
How metals, ceramics, polymers, glass and composites compare in toughness, density, melting point, conductivity and strength, what a composite is, and choosing materials for windows, furnaces, bicycles, cables, kettles and bridges.
What you need to know
Answer each one before you reveal it.
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Key term
Compare the density of aluminium with the density of steel.
Key term
How does the melting point of a typical polymer compare with that of a clay ceramic?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Which stands up better to a sharp blow, a metal or a clay ceramic, and why?
Model answer
The metal, because it bends or dents, while a ceramic is brittle and shatters.
- 2
Compare the density of aluminium with the density of steel.
Model answer
Aluminium is roughly a third as dense as steel.
- 3
How does the melting point of a typical polymer compare with that of a clay ceramic?
Model answer
A polymer softens or melts at a few hundred degrees Celsius, while a ceramic withstands well over a thousand.
- 4
Compare the electrical conductivity of a metal with that of a polymer.
Model answer
A metal conducts extremely well, while a polymer is an insulator that conducts many times less.
- 5
Compare the strength of glass in compression with its strength in tension.
Model answer
Glass is far stronger in compression than in tension, which is why it cracks when it is bent.
- 6
Which is stronger for its mass, a carbon fibre composite or steel?
Model answer
The composite, because it has a comparable strength but a much lower density.
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