Key term
OCR GCSE Combined Science Chemistry J250
Chemical Reactions
Topic overviewWriting formulae of elements and compoundsBalanced equations, and deducing formulae from ionsIonic equations, and state symbolsThe mole and the Avogadro constantConservation of mass, and changes of mass in open systemsStoichiometry, and calculating reacting massesExothermic and endothermic reactions, and reaction profilesActivation energy, and bond energy calculationsOxidation and reduction, by oxygen and by electronsAcids, alkalis and neutralisationThe ionic equation for neutralisation, and reactions of acidsDilute and concentrated, weak and strongThe pH scale, and hydrogen ion concentrationpH as a factor of ten, and measuring pHProducts 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 electrolysisBiological methods of metal extractionLife 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
Topic overviewMass of solute, concentration and dilution calculationsMeasuring the rate of a reaction, and rate graphsFactors affecting rate, and collision theorySurface area and rateCatalysts and how they workReversible reactions and dynamic equilibriumChanging the conditions of an equilibriumActivation energy, and enzymes as catalysts
Particles
Predicting and Identifying Reactions
Reactivity of metals with water and acids
- 3 things to know
- Paper 10 (Chemistry)
Overview
Why metals form positive ions when they react with water or acid, the products with acid, why potassium reacts faster than calcium, the metals that react with cold water, magnesium with steam, why copper does not react with acid while zinc and iron react slowly, ordering metals by fair tests and displacement, the temperature rise, cleaning with emery paper, and aluminium's oxide layer.
What you need to know
Answer each one before you reveal it.
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Key term
Explain why potassium reacts far more vigorously with cold water than calcium does.
Key term
Name four metals that react noticeably with cold water.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What happens to a metal atom when the metal reacts with water or with a dilute acid?
Model answer
It loses electrons and becomes a positive ion, so the metal is oxidised.
- 2
What does the position of a metal high up in the reactivity series tell you about its atoms?
Model answer
Its atoms lose electrons and form positive ions very easily.
- 3
What two products are formed when a metal reacts with a dilute acid?
Model answer
A salt and hydrogen gas.
- 4
Explain why potassium reacts far more vigorously with cold water than calcium does.
Model answer
Potassium loses its outer electron and forms its positive ion much more readily than calcium, so its reaction is much faster.
- 5
Name four metals that react noticeably with cold water.
Model answer
Potassium, sodium, lithium and calcium.
- 6
Compare how magnesium reacts with cold water and with steam.
Model answer
It reacts extremely slowly with cold water, but burns vigorously in steam to form magnesium oxide and hydrogen.
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