Key term
AQA GCSE Combined Science Chemistry 8464
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 7
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 fullerenes
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 neutralisationStrong and weak acidsThe process of electrolysis, and molten ionic compoundsUsing electrolysis to extract metalsElectrolysis of aqueous solutionsRepresentation of reactions at electrodes as half equations
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
Quantitative Chemistry
The Rate and Extent of Chemical Change
Topic overviewMeasuring the mean rate of a reactionRate from graphs, and the gradient of a tangentFactors which affect the rates of chemical reactionsCollision theory and activation energyCatalystsReversible reactions and dynamic equilibriumThe effect of changing conditions on equilibriumThe effect of changing concentrationThe effect of temperature changes on equilibriumThe effect of pressure changes on equilibrium
Chemical Analysis
Chromatography
- 3 things to know
- Chemistry Paper 2
Overview
The stationary and mobile phases, what decides how far a substance travels, how Rf values are defined and calculated, reading purity from a chromatogram, and why the start line is pencil and the solvent starts below it.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Evaluation
What decides how far a substance travels during chromatography?
Key term
How is the Rf value of a compound defined?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What are the two phases involved in any form of chromatography?
Model answer
A stationary phase, which stays still, and a mobile phase, which moves through it.
- 2
What can chromatography do for a mixture?
Model answer
It separates the substances in the mixture and gives information that helps to identify them.
- 3
What decides how far a substance travels during chromatography?
Model answer
How that substance is distributed between the mobile phase and the stationary phase.
- 4
Explain why one substance in a mixture travels further up the paper than another.
Model answer
It is held less strongly by the stationary phase and carried more readily by the moving solvent.
- 5
How is the Rf value of a compound defined?
Model answer
It is the distance moved by the compound, measured to the centre of its spot, divided by the distance moved by the solvent.
- 6
A spot moves 3.6 cm from the origin while the solvent moves 8.0 cm. Calculate its Rf value.
Model answer
Rf is 3.6 ÷ 8.0, which is 0.45.
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