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
pH as a factor of ten, and measuring pH
- 2 things to know
- Paper 9 (Chemistry)
Overview
How pH changes by one unit for each tenfold change in hydrogen ion concentration, calculating those factors between pH values, what universal indicator and litmus show and their colours, using, rinsing and calibrating a pH meter and its advantage over indicator, and what the resolution of a meter means.
What you need to know
Answer each one before you reveal it.
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Key term
What happens to the pH when the hydrogen ion concentration falls by a factor of ten?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What happens to the pH of a solution when its hydrogen ion concentration increases by a factor of ten?
Model answer
The pH falls by one unit.
- 2
What happens to the pH when the hydrogen ion concentration falls by a factor of ten?
Model answer
The pH rises by one unit.
- 3
How many times greater is the hydrogen ion concentration at pH 2 than at pH 4?
Model answer
100 times greater.
- 4
An acid of pH 3 is diluted until its pH is 5. By what factor has the hydrogen ion concentration fallen?
Model answer
By a factor of 100.
- 5
How many times more concentrated in hydrogen ions is a solution of pH 1 than one of pH 6?
Model answer
100 000 times, because the concentration changes tenfold for each of the five pH units.
- 6
The hydrogen ion concentration of a solution of pH 4 is multiplied by 1000. What is its new pH?
Model answer
1.
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