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
Chemical Reactions
The mole and the Avogadro constant
- 3 things to know
- Paper 9 (Chemistry)
Overview
What the Avogadro constant and a mole are, counting the atoms, molecules and ions in a number of moles, the mass of a single atom or molecule, why chemists use the mole, and converting between mass and moles with relative formula mass for carbon dioxide, calcium carbonate, magnesium, water and sodium hydroxide.
What you need to know
Answer each one before you reveal it.
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Key term
What is a mole of a substance?
Numbers
How many atoms are there in one mole of carbon?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is the value of the Avogadro constant?
Model answer
6.02 × 10²³ per mole.
- 2
What is a mole of a substance?
Model answer
The amount of that substance containing 6.02 × 10²³ particles.
- 3
How many atoms are there in one mole of carbon?
Model answer
6.02 × 10²³ atoms.
- 4
How many molecules are there in 2 mol of carbon dioxide?
Model answer
1.204 × 10²⁴ molecules.
- 5
One mole of carbon atoms has a mass of 12 g. Calculate the mass of a single carbon atom.
Model answer
12 ÷ (6.02 × 10²³) = 1.99 × 10⁻²³ g.
- 6
The relative formula mass of water is 18. Calculate the mass of one water molecule.
Model answer
18 ÷ (6.02 × 10²³) = 2.99 × 10⁻²³ g.
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