Key term
Edexcel GCSE Combined Science Chemistry 1SC0
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 compounds and ionic equationsNaming 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 decimetreMoles and the Avogadro constantLimiting reactants and stoichiometry
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 phenolphthaleinHydrogen ion concentration and the pH scaleInvestigating pH change when neutralising an acidDilute and concentrated, weak and strong acidsBases 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 electrodesWriting half equationsOxidation and reduction at the electrodesElectrolysis of copper sulfate solutionInvestigating the electrolysis of copper sulfate
Extracting Metals and Equilibria
Topic overviewInvestigating the reactivity of metalsDisplacement reactions as redox reactionsThe reactivity seriesOres, oxidation and reductionChoosing a method to extract a metalBiological methods of metal extractionCorrosion resistance and recycling metalsLife cycle assessmentReversible reactions and dynamic equilibriumThe Haber process and its conditionsChanging the position of an equilibrium
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
Topic overviewInvestigating the rate of a reactionMeasuring rate and interpreting rate graphsCollision theory and factors affecting rateCatalysts and enzymesExothermic and endothermic changesBond breaking, bond making and the overall energy changeBond energies, activation energy and reaction profiles
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
Key Concepts in Chemistry
Relative formula mass and percentage composition
- 1 thing to know
- Papers 3 and 4
Overview
Adding up relative formula masses for CO₂, CaCO₃, Ca(OH)₂ and H₂SO₄, finding the percentage by mass of an element, and working out empirical formulae from reacting masses.
What you need to know
Answer each one before you reveal it.
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Questions from this subtopic
Each one with the model answer underneath.
- 1
How is the relative formula mass of a compound worked out?
Model answer
Add together the relative atomic masses of every atom shown in its formula.
- 2
Calculate the relative formula mass of carbon dioxide, CO₂. Relative atomic masses: C = 12, O = 16.
Model answer
12 + (2 × 16) = 44.
- 3
Calculate the relative formula mass of calcium carbonate, CaCO₃. Relative atomic masses: Ca = 40, C = 12, O = 16.
Model answer
40 + 12 + (3 × 16) = 100.
- 4
Calculate the relative formula mass of calcium hydroxide, Ca(OH)₂. Relative atomic masses: Ca = 40, O = 16, H = 1.
Model answer
40 + 2 × (16 + 1) = 74.
- 5
Calculate the relative formula mass of sulfuric acid, H₂SO₄. Relative atomic masses: H = 1, S = 32, O = 16.
Model answer
(2 × 1) + 32 + (4 × 16) = 98.
- 6
State how the percentage by mass of an element in a compound is found.
Model answer
Divide the total relative atomic mass of that element by the relative formula mass and multiply by 100.
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