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
Monitoring and Controlling Chemical Reactions
Carrying out an acid–alkali titration
- 3 things to know
- Paper 2
Overview
The pipette, burette and white tile used in a titration, what the end point is, the colour changes of phenolphthalein and methyl orange, reading a burette at the meniscus, why a rough titration comes first and the flask is swirled, and what concordant titres are and why only they are averaged.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
In a titration, which piece of apparatus delivers the second solution in a measured but variable volume?
Key term
Name two indicators used in acid–alkali titrations and give the colour change of each as acid is added to alkali.
Questions from this subtopic
Each one with the model answer underneath.
- 1
In a titration, which piece of apparatus is used to measure the accurate fixed volume of solution placed in the conical flask?
Model answer
A pipette, used with a safety filler, measures a fixed volume such as 25.0 cm³ into the conical flask.
- 2
In a titration, which piece of apparatus delivers the second solution in a measured but variable volume?
Model answer
A burette, which is filled to the zero mark and read before and after the solution is run in.
- 3
What is meant by the end point of a titration?
Model answer
It is the point at which the indicator changes colour permanently, showing that the two solutions have just reacted completely.
- 4
Why is a white tile placed under the conical flask during a titration?
Model answer
It makes the colour change of the indicator much easier to see, so the end point is judged more accurately.
- 5
Name two indicators used in acid–alkali titrations and give the colour change of each as acid is added to alkali.
Model answer
Phenolphthalein changes from pink to colourless, and methyl orange changes from yellow to red.
- 6
How should a burette be read correctly?
Model answer
Read it at eye level from the bottom of the meniscus, to the nearest 0.05 cm³.
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