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
Nanoparticles: size and surface area to volume
- 2 things to know
- Paper 1
Overview
The size range of nanoparticles, nanometres in metres, how many atoms or molecules fit across one, why they cannot be seen with a light microscope, calculating the surface area to volume ratio of cubes and how it changes as particles get smaller, and why nanoparticles make effective catalysts, react faster and behave differently from the bulk material.
What you need to know
Answer each one before you reveal it.
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Key term
How does the diameter of a typical atom compare with a nanometre?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What range of sizes counts as nanoparticle size?
Model answer
Roughly 1 nm to 100 nm across.
- 2
What is one nanometre in metres?
Model answer
It is 1 × 10⁻⁹ m.
- 3
How does the diameter of a typical atom compare with a nanometre?
Model answer
An atom is about 0.1 nm across, so roughly ten atoms would sit side by side across one nanometre.
- 4
Roughly how many atoms would lie across a nanoparticle 10 nm wide?
Model answer
About 100, since each atom is about 0.1 nm across.
- 5
A water molecule is about 0.3 nm across. Roughly how many would fit across a particle 30 nm wide?
Model answer
About 100, because 30 ÷ 0.3 = 100.
- 6
Why can nanoparticles not be seen with an ordinary light microscope?
Model answer
Because they are far smaller than the wavelength of visible light, which is several hundred nanometres.
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