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
Predicting and Identifying Reactions
Identifying a species from test results
- 1 thing to know
- Paper 2
Overview
Why a cation test and an anion test are both needed, naming salts from flame colours and precipitates with sodium hydroxide, silver nitrate and barium chloride, and why silver nitrate without acid is unsafe.
What you need to know
Answer each one before you reveal it.
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Questions from this subtopic
Each one with the model answer underneath.
- 1
Why are two separate tests usually needed to identify an unknown salt?
Model answer
One test identifies the positive metal ion and the other identifies the negative ion, and both are needed to name the compound.
- 2
A solution gives an orange-red flame, a white precipitate with sodium hydroxide that does not dissolve in excess, and a white precipitate with acidified silver nitrate. Name the salt.
Model answer
Calcium chloride.
- 3
A blue solution gives a blue precipitate with sodium hydroxide and a white precipitate with acidified barium chloride. Name the salt.
Model answer
Copper(II) sulfate.
- 4
A green solid gives a green precipitate with sodium hydroxide and fizzes with dilute acid, giving a gas that turns limewater milky. Name the solid.
Model answer
Iron(II) carbonate.
- 5
A solution gives a lilac flame and a yellow precipitate with acidified silver nitrate. Name the salt.
Model answer
Potassium iodide.
- 6
A colourless solution gives a white precipitate with sodium hydroxide that dissolves in excess, and a cream precipitate with acidified silver nitrate. Name the salt.
Model answer
Zinc bromide.
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