Key term
AQA GCSE Chemistry 8462
Atomic Structure and the Periodic Table
Topic overviewAtoms, elements and compoundsWord equations, symbols and balanced equationsMixturesFrom the plum pudding model to the nuclear modelBohr, Chadwick and the modern model of the atomRelative electrical charges of subatomic particlesSize and mass of atomsRelative atomic mass and electronic structureThe periodic tableDevelopment of the periodic tableMetals and non-metalsGroup 0Group 1Group 7Transition metals, and how they differ from Group 1
Bonding, Structure, and the Properties of Matter
Topic overviewChemical bonds, including metallic bondingIonic bondingIonic compoundsCovalent bonding and how it is representedThe three states of matter and changes of statePredicting state, state symbols, and the limits of the particle modelProperties of ionic compoundsProperties of small moleculesPolymers and giant covalent structuresProperties of metals and alloys, and why metals conductDiamond and graphiteGraphene and fullerenesSizes of particles and their propertiesUses of nanoparticles
Chemical Analysis
Chemical Changes
Topic overviewThe reactivity seriesMetal oxides, extraction, and redox in terms of electronsAcids reacting with metals, neutralisation and saltsSoluble saltsThe pH scale and neutralisationTitrationsThe process of electrolysis, and molten ionic compoundsUsing electrolysis to extract metalsElectrolysis of aqueous solutions
Chemistry of the Atmosphere
Topic overviewThe Earth's early atmosphereHow oxygen increased and carbon dioxide decreasedThe gases in today's atmosphere, and which are greenhouse gasesHuman activities which contribute to an increase in greenhouse gases in the atmosphereGlobal climate change and carbon footprintsAtmospheric pollutants from fuels, and their effects
Energy Changes
Organic Chemistry
Topic overviewCrude oil, hydrocarbons and alkanesFractional distillation and petrochemicalsProperties of hydrocarbonsCracking, and testing alkenes with bromine waterWhy cracking is useful, and equations for itStructure and formulae of alkenesReactions of alkenesAlcoholsCarboxylic acidsAddition polymerisationAmino acids, DNA and naturally occurring polymers
Quantitative Chemistry
The Rate and Extent of Chemical Change
Using Resources
Topic overviewUsing the Earth's resources and sustainable developmentProducing potable water in the UKDesalination, and analysing water samplesWaste water treatmentLife cycle assessmentWays of reducing the use of resourcesCorrosion and its preventionAlloys as useful materialsGlass, clay ceramics and polymersComposites, and comparing materialsThe Haber processProduction and uses of NPK fertilisers
Quantitative Chemistry
Percentage yield
- 3 things to know
- Paper 1
Overview
Why the theoretical mass of product is not always obtained, including reversible reactions, losses during separation and side reactions, the meaning of yield and percentage yield, the percentage yield equation and why it cannot exceed 100%, and worked percentage yield calculations.
What you need to know
Answer each one before you reveal it.
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Key term
Give three reasons why the full theoretical mass of a product may not be obtained.
Process
Name a stage of a preparation at which product is commonly lost.
Questions from this subtopic
Each one with the model answer underneath.
- 1
No atoms are gained or lost in a reaction, so why is the calculated mass of product not always obtained?
Model answer
Some of the product is not made or not collected, so in practice less than the theoretical mass is recovered.
- 2
Give three reasons why the full theoretical mass of a product may not be obtained.
Model answer
The reaction may be reversible and not go to completion, some product may be lost when it is separated from the mixture, and some reactants may react in ways other than the expected reaction.
- 3
Explain how a reversible reaction lowers the mass of product obtained.
Model answer
It does not go to completion, so some of the reactants are still present at the end instead of having been turned into product.
- 4
Name a stage of a preparation at which product is commonly lost.
Model answer
When the product is separated from the reaction mixture, for example some is left behind on filter paper or in the container during transfer.
- 5
What is meant by saying that some reactants may react in ways different to the expected reaction?
Model answer
They take part in side reactions that make other products, so less of the wanted product is formed.
- 6
What is meant by the yield of a reaction?
Model answer
It is the amount of product that is actually obtained.
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