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
The pH scale, acidity and alkalinity
- 3 things to know
- Paper 3 (Chemistry)
Overview
What pH measures, the 0 to 14 scale and its acidic, neutral and alkaline values, comparing how acidic or alkaline two solutions are, and why a pH value says more than simply calling a solution acidic.
What you need to know
Answer each one before you reveal it.
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Key term
Which pH values show that a solution is acidic?
Key term
Which pH values show that a solution is alkaline?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What does pH measure?
Model answer
How acidic or how alkaline a solution is.
- 2
What is the range of the pH scale?
Model answer
From 0 to 14.
- 3
What pH value does a neutral solution have?
Model answer
7.
- 4
Which pH values show that a solution is acidic?
Model answer
Values below 7.
- 5
Which pH values show that a solution is alkaline?
Model answer
Values above 7.
- 6
Which is the more acidic solution, one of pH 1 or one of pH 5?
Model answer
The one of pH 1, because the lower the pH the more acidic the solution.
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