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
Products at the electrodes, and molten ionic compounds
- 3 things to know
- Paper 3 (Chemistry)
Overview
What cations and anions are and which electrode each moves to, what forms at the cathode and the anode, inert electrodes, why a compound must be molten or dissolved, and predicting the products of electrolysing molten sodium chloride, lead bromide, magnesium oxide and potassium iodide, with the difficulties of electrolysing molten sodium chloride.
What you need to know
Answer each one before you reveal it.
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Key term
What is an anion, and which electrode does it move to?
Key term
Which electrode is the negative one, and which is the positive one?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is a cation, and which electrode does it move to?
Model answer
A positively charged ion, which moves to the cathode.
- 2
What is an anion, and which electrode does it move to?
Model answer
A negatively charged ion, which moves to the anode.
- 3
Which electrode is the negative one, and which is the positive one?
Model answer
The cathode is negative and the anode is positive.
- 4
Which kinds of substance are produced at the cathode?
Model answer
A metal, or hydrogen.
- 5
Which kind of substance is produced at the anode?
Model answer
A non-metal, such as a halogen or oxygen.
- 6
Why does each type of ion travel to a particular electrode?
Model answer
Opposite charges attract, so positive ions are drawn to the negative cathode and negative ions to the positive anode.
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