Key term
Edexcel GCSE Chemistry 1CH0
Key Concepts in Chemistry
Topic overviewFormulae, word equations and balanced equationsHazard symbols and assessing riskThe changing model of the atomProtons, neutrons and electronsThe nucleus, mass number and atomic massElements and isotopesCalculating particle numbers and relative atomic massMendeleev's periodic tableHow the modern periodic table is arrangedElectronic configuration and the periodic tableHow ionic bonds formIons in ionic compoundsFormulae of ionic compoundsNaming compounds and the ionic latticeCovalent bonds and moleculesDot and cross diagrams for simple moleculesClassifying substances and the properties of ionic compoundsProperties of simple molecular substances, and forms of carbonGraphite and diamondFullerenes and graphenePolymers and models of bondingThe properties of metalsRelative formula mass and percentage compositionEmpirical and molecular formulaeConservation of mass in closed and open systemsReacting masses from balanced equationsConcentration in grams per cubic decimetre
States of Matter and Mixtures
Topic overviewThe three states of matter and changes of stateEnergy changes during changes of state, and predicting statePure substances and melting point dataChoosing a separation techniqueSeparating a mixture in practicePaper chromatography and interpreting a chromatogramInvestigating inks by distillation and chromatographyMaking water potable
Chemical Changes
Topic overviewAcids, alkalis and the pH scaleIndicators: litmus, methyl orange and phenolphthaleinInvestigating pH change when neutralising an acidBases and alkalisReactions of acids, and testing for hydrogen and carbon dioxideNeutralisation and its ionic equationPreparing soluble salts from insoluble and soluble reactantsPreparing pure, dry copper sulfate crystalsCarrying out an acid-alkali titrationSolubility rulesPredicting precipitates and preparing an insoluble saltElectrolytes and what electrolysis isMovement of ions and predicting the products of molten electrolysisElectrolysis with inert electrodesElectrolysis of copper sulfate solutionInvestigating the electrolysis of copper sulfate
Extracting Metals and Equilibria
Transition Metals, Quantitative Chemistry and Industrial Processes
Topic overviewTransition metals and their propertiesCorrosion and electroplatingPreventing rustingAlloys and alloy steelsHow the uses of metals relate to their propertiesCarrying out an accurate titrationPercentage yieldAtom economyThe Haber processFertilisers and ammonium saltsPreparing ammonium sulfate in the lab and in industryChemical cells and fuel cellsEvaluating fuel cells
Groups in the Periodic Table
Topic overviewThe groups of the periodic table, and the alkali metalsReactions of the alkali metals with waterThe pattern in alkali metal reactivity and why it happensPhysical properties of the halogensThe test for chlorine, and halogens reacting with metalsHydrogen halides, and explaining halogen reactivityDisplacement reactions of the halogensGroup 0: the noble gases
Rates of Reaction and Energy Changes
Fuels and Earth Science
Topic overviewHydrocarbons and crude oilFractional distillation and the fractionsProperties of the fractions and homologous seriesComplete and incomplete combustionCarbon monoxide and sootPollutants and acid rainHydrogen and fossil fuels comparedCracking and why it is necessaryThe Earth's early atmosphereHow the oceans formed and how oxygen appearedThe test for oxygen and the greenhouse gasesToday's atmosphere and evidence for climate change
Chemical Analysis, Organic Chemistry and Materials
Topic overviewWhy an ion test must be unique, and flame testsTests for metal ions and for ammoniaTests for carbonate, sulfate and halide ionsIdentifying the ions in an unknown saltInstrumental methods and flame photometryAlkanes and why they are saturatedAlkenes and why they are unsaturatedReactions of alkenes, and combustionWhat a polymer is, and how poly(ethene) formsOther addition polymers, and monomers from polymersUses of polymers, and natural polymers including DNAProblems with polymers and recyclingAlcohols and the -OH functional groupComparing the energy released by alcohol fuelsMaking ethanol by fermentation and distillationCarboxylic acids and the -COOH functional groupOxidising alcohols to carboxylic acids, and homologous seriesThe size of nanoparticlesUses and risks of nanoparticlesChoosing a material for a use
Chemical Analysis, Organic Chemistry and Materials
What a polymer is, and how poly(ethene) forms
- 2 things to know
- Paper 2
Overview
What polymers, monomers and repeating units are and why a polymer's relative molecular mass is an average, and how ethene's double bond opens in addition polymerisation to form poly(ethene) with the repeating unit –CH₂–CH₂–.
What you need to know
Answer each one before you reveal it.
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Key term
Why is the relative molecular mass of a polymer described as an average rather than a fixed value?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is a polymer?
Model answer
A polymer is a substance with a high average relative molecular mass made from many small repeating units joined together.
- 2
What name is given to the small molecules that join together to make a polymer?
Model answer
They are called monomers.
- 3
Why is the relative molecular mass of a polymer described as an average rather than a fixed value?
Model answer
Different polymer molecules in the same sample contain different numbers of repeating units, so their masses vary.
- 4
How does the relative molecular mass of a polymer molecule compare with that of the monomer it was made from?
Model answer
The polymer molecule has a far higher relative molecular mass because it contains many monomer units joined together.
- 5
What is meant by the repeating unit of a polymer?
Model answer
It is the small group of atoms that occurs over and over again along the polymer chain.
- 6
How can a polymer molecule containing thousands of atoms be represented simply?
Model answer
It can be shown by its repeating unit, since the same unit is repeated along the whole chain.
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