Key term
OCR GCSE Chemistry A J248
Chemical Reactions
Topic overviewWriting formulae of elements and compoundsBalanced equations, and deducing formulae from ionsIonic equations, and state symbolsThe mole and the Avogadro constantConservation of mass, and changes of mass in open systemsStoichiometry, and calculating reacting massesExothermic and endothermic reactions, and reaction profilesActivation energy, and bond energy calculationsOxidation and reduction, by oxygen and by electronsAcids, alkalis and neutralisationThe ionic equation for neutralisation, and reactions of acidsDilute and concentrated, weak and strongThe pH scale, and hydrogen ion concentrationpH as a factor of ten, and measuring pHProducts 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 electrolysisBiological methods of metal extractionRate against yield in industry, and reaction conditionsThe 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 polymerisationCondensation polymerisation, and making a polymerDNA 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 overviewConcentration in mol/dm³, and titrationTitration calculations, and the mass of a soluteMolar gas volume and the volumes of gasesTheoretical mass and percentage yieldAtom economy, and choosing a reaction pathwayMeasuring the rate of a reaction, and rate graphsFactors affecting rate, and collision theorySurface area and rateCatalysts and how they workReversible reactions and dynamic equilibriumChanging the conditions of an 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
Chemical Reactions
Ionic equations, and state symbols
- 3 things to know
- Paper 3
Overview
What an ionic equation and a spectator ion are, why charge must balance, ionic equations for the precipitates copper(II) hydroxide, silver chloride and barium sulfate and for magnesium with acid, what the state symbols s, l, g and aq mean, and adding them to equations such as zinc or marble chips with acid.
What you need to know
Answer each one before you reveal it.
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Key term
What is a spectator ion?
Key term
Besides the atoms, what else must balance on the two sides of an ionic equation?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is an ionic equation?
Model answer
An equation that shows only the species that actually change during the reaction, leaving out the ions that do not react.
- 2
What is a spectator ion?
Model answer
An ion that is present in the mixture but is unchanged by the reaction, appearing on both sides of the full equation.
- 3
Besides the atoms, what else must balance on the two sides of an ionic equation?
Model answer
The total electrical charge must be the same on both sides.
- 4
Write the ionic equation for copper(II) hydroxide precipitating when sodium hydroxide solution is added to copper(II) sulfate solution.
Model answer
Cu²⁺(aq) + 2OH⁻(aq) → Cu(OH)₂(s).
- 5
Write the ionic equation for silver chloride forming when silver nitrate solution is mixed with sodium chloride solution.
Model answer
Ag⁺(aq) + Cl⁻(aq) → AgCl(s).
- 6
Write the ionic equation for magnesium reacting with a dilute acid.
Model answer
Mg(s) + 2H⁺(aq) → Mg²⁺(aq) + H₂(g).
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