Key term
OCR GCSE Combined Science Chemistry J250
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 structures
Global Challenges
Topic overviewExtracting metals by reduction and by electrolysisLife cycle assessmentRecycling, and the decisions behind itFractional distillation of crude oilThe fractions, and crude oil as a feedstockDependence on hydrocarbons, and crackingThe 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
Particles
Chemical Reactions
Balanced equations, and deducing formulae from ions
- 3 things to know
- Paper 3 (Chemistry)
Overview
Balanced equations for sodium in chlorine, methane burning, potassium in water and calcium carbonate decomposing, why only the large numbers change, and deducing formulae such as Al₂O₃ and Ca(NO₃)₂ from ion charges.
What you need to know
Answer each one before you reveal it.
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Key term
Write the balanced equation for the complete combustion of methane.
Key term
Write the balanced equation for potassium reacting with water.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Write the balanced equation for sodium burning in chlorine.
Model answer
2Na + Cl₂ → 2NaCl.
- 2
Write the balanced equation for the complete combustion of methane.
Model answer
CH₄ + 2O₂ → CO₂ + 2H₂O.
- 3
Write the balanced equation for potassium reacting with water.
Model answer
2K + 2H₂O → 2KOH + H₂.
- 4
Write the balanced equation for the thermal decomposition of calcium carbonate.
Model answer
CaCO₃ → CaO + CO₂.
- 5
Write the balanced equation for hydrogen burning in oxygen.
Model answer
2H₂ + O₂ → 2H₂O.
- 6
Write the balanced equation for aluminium reacting with oxygen to form aluminium oxide.
Model answer
4Al + 3O₂ → 2Al₂O₃.
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