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
Elements, Compounds and Mixtures
Choosing a purification method
- 3 things to know
- Paper 1
Overview
Matching filtration, simple distillation, crystallisation and fractional distillation to mixtures, the property each relies on, purifying rock salt, choosing paper or thin layer chromatography, and how gas chromatography works.
What you need to know
Answer each one before you reveal it.
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Key term
Which technique would you suggest to obtain pure water from seawater?
Key term
Which technique would you suggest to obtain solid copper sulfate from copper sulfate solution?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Which technique would you suggest to separate sand from water, and why?
Model answer
Filtration, because sand is insoluble and stays on the filter paper while the water passes through.
- 2
Which technique would you suggest to obtain pure water from seawater?
Model answer
Simple distillation, because the water evaporates and is condensed while the dissolved salts are left behind.
- 3
Which technique would you suggest to obtain solid copper sulfate from copper sulfate solution?
Model answer
Crystallisation, because the solid is soluble and forms crystals as the solution is concentrated and cooled.
- 4
Two liquids mix completely and boil at 78 °C and 100 °C. Which technique separates them?
Model answer
Fractional distillation, because they have different boiling points but are close enough to need a fractionating column.
- 5
What property of the components must differ for any kind of distillation to work?
Model answer
Their boiling points must be different.
- 6
What difference in properties does filtration rely on?
Model answer
It relies on one component being insoluble in the liquid while the other is a liquid or is dissolved in it.
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