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
Instrumental methods of analysis
- 3 things to know
- Paper 2
Overview
The sensitivity, accuracy and speed of machine methods, their cost and need for trained operators and reference data, why they suit mixtures and tiny samples, and reading a mass spectrum.
What you need to know
Answer each one before you reveal it.
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Key term
Give two drawbacks of machine methods of analysis.
Key term
A sample contains several different metal ions. Why would a machine method identify them better than a flame test?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Give three advantages that machine methods of chemical analysis have over tests done in a test tube.
Model answer
They are more sensitive, more accurate and much faster.
- 2
What does it mean to say that an analytical instrument is very sensitive?
Model answer
It can detect and identify extremely small amounts of a substance, far less than a test tube test would show.
- 3
Why does the speed of an analytical machine matter in a testing laboratory?
Model answer
Many samples can be analysed in a short time, so results such as water quality or drug tests are available quickly.
- 4
Why is a machine result usually more accurate than a colour change judged by eye?
Model answer
The machine measures the sample directly rather than relying on a person's judgement of a colour, so there is less chance of a mistake.
- 5
Why are machine methods valuable when only a tiny sample is available, such as at a crime scene?
Model answer
They can identify a substance from a very small sample, whereas chemical tests need enough material to see a precipitate or a colour.
- 6
Give two drawbacks of machine methods of analysis.
Model answer
The equipment is expensive, and it needs trained operators and a set of reference results to interpret.
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