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
Alloys, and the corrosion of metals
- 3 things to know
- Paper 2
Overview
What an alloy is and why it is harder than the pure metal, the make-up and uses of steel, brass, bronze, solder and duralumin, what corrosion is, the conditions for rusting and the experiment that shows them, why salt speeds it up, why aluminium and copper are protected by their corrosion layers, and preventing rusting with barriers, galvanising and sacrificial protection by zinc or magnesium.
What you need to know
Answer each one before you reveal it.
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Key term
Explain why an alloy is usually harder than the pure metal it is made from.
Key term
What is steel made from, and give a use for it.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is an alloy?
Model answer
A mixture of a metal with one or more other elements.
- 2
Explain why an alloy is usually harder than the pure metal it is made from.
Model answer
The atoms of the added element are a different size and disrupt the regular layers, so the layers cannot slide over one another easily.
- 3
What is steel made from, and give a use for it.
Model answer
Iron with a small amount of carbon, used for buildings, bridges and car bodies.
- 4
Name the two metals in brass and give a use for it.
Model answer
Copper and zinc, used for taps, door fittings and musical instruments.
- 5
Name the two metals in bronze and give a use for it.
Model answer
Copper and tin, used for statues, bells and ships' propellers.
- 6
What is solder made from, and why is its low melting point useful?
Model answer
Tin mixed with lead or another metal; it melts easily so it can join electrical components without overheating them.
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