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
Chemical Reactions
Electrolysis of aqueous solutions
- 3 things to know
- Paper 1
Overview
The hydrogen and hydroxide ions from water, the rules for what forms at each electrode, the products from sodium chloride and copper(II) sulfate solutions, and the half equations for hydrogen, chlorine, oxygen and copper.
What you need to know
Answer each one before you reveal it.
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Key term
What decides whether a metal or hydrogen is produced at the cathode in an aqueous solution?
Key term
What decides which product forms at the anode in an aqueous solution?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Which extra ions are present in any aqueous solution besides those of the dissolved compound?
Model answer
Hydrogen ions and hydroxide ions, which come from the water itself.
- 2
What decides whether a metal or hydrogen is produced at the cathode in an aqueous solution?
Model answer
Hydrogen is produced unless the metal is less reactive than hydrogen, in which case the metal is deposited.
- 3
What decides which product forms at the anode in an aqueous solution?
Model answer
Oxygen is produced unless a halide ion is present, in which case the halogen is released instead.
- 4
Name the products of the electrolysis of sodium chloride solution using inert electrodes.
Model answer
Hydrogen at the cathode and chlorine at the anode.
- 5
Why is sodium not produced when sodium chloride solution is electrolysed?
Model answer
Sodium is more reactive than hydrogen, so the hydrogen ions from the water gain the electrons instead.
- 6
Name the products of the electrolysis of copper(II) sulfate solution using inert electrodes.
Model answer
Copper at the cathode and oxygen at the anode.
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