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
Elements, Compounds and Mixtures
Formulations, and separating mixtures
- 3 things to know
- Paper 3 (Chemistry)
Overview
What a formulation is and why it is never pure, examples such as paints, medicines and brass, the jobs of the pigment and solvent in a paint, why proportions matter and alloys are harder than pure metals, and how filtration, crystallisation, simple distillation and fractional distillation separate mixtures.
What you need to know
Answer each one before you reveal it.
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Key term
In a paint, what jobs are done by the pigment and by the solvent?
Key term
Why do the proportions of the components in a formulation matter so much?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is a formulation?
Model answer
It is a mixture designed as a useful product, in which each component is present in a measured quantity for a particular purpose.
- 2
Why is a formulation never a pure substance?
Model answer
Because it contains several different substances mixed together and not chemically combined.
- 3
Give three everyday products that are formulations.
Model answer
Paints, medicines and cleaning products are all formulations, as are fuels, fertilisers and alloys.
- 4
Why is brass described as a formulation?
Model answer
Because it is a mixture of copper and zinc combined in measured proportions to give properties such as hardness that neither metal has alone.
- 5
In a paint, what jobs are done by the pigment and by the solvent?
Model answer
The pigment provides the colour, and the solvent allows the paint to be spread thinly before evaporating to leave the coloured film behind.
- 6
Why do the proportions of the components in a formulation matter so much?
Model answer
Because the properties of the finished product depend on the proportions, so changing them gives a product that behaves differently.
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