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
Global Challenges
Chemical cells and fuel cells
- 2 things to know
- Paper 2
Overview
What a chemical cell is, why it runs until a reactant is used up and a battery goes flat, the electrolyte and the difference in reactivity that sets the potential difference, making a cell last longer, the hydrogen–oxygen fuel cell with its equation, electrodes and water product, its advantages and disadvantages in cars and spacecraft, and whether a hydrogen car is free of carbon dioxide emissions.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
For how long does a chemical cell produce a potential difference?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is a chemical cell?
Model answer
A device in which a chemical reaction produces a potential difference between two electrodes, which can drive a current round a circuit.
- 2
For how long does a chemical cell produce a potential difference?
Model answer
Until one of the reactants has been used up, after which the reaction stops and the potential difference falls to zero.
- 3
Explain why a non-rechargeable battery eventually goes flat.
Model answer
The chemicals inside it are used up by the reaction, so no further reaction can take place to produce a potential difference.
- 4
What must be present between the two electrodes of a chemical cell, and why?
Model answer
An electrolyte, so that ions can move between the electrodes and complete the circuit.
- 5
In a simple cell made from two different metals, what decides how large the potential difference is?
Model answer
How far apart the two metals are in reactivity: the bigger the difference, the larger the potential difference.
- 6
Why does a cell with the same metal used for both electrodes produce no potential difference?
Model answer
There is no difference in reactivity between the electrodes, so no overall reaction takes place.
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