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
State symbols in equations
- 3 things to know
- Paper 3 (Chemistry)
Overview
What the state symbols s, l, g and aq stand for, why the water made in neutralisation is a liquid, the symbols for a precipitate and a molten salt, and adding state symbols to the reactions of zinc and marble chips with acid.
What you need to know
Answer each one before you reveal it.
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Key term
Add state symbols to the reaction of zinc metal with dilute sulfuric acid.
Key term
Which state symbol shows that a precipitate has formed in a solution?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What do the state symbols s, l, g and aq stand for?
Model answer
Solid, liquid, gas and aqueous solution.
- 2
What does the state symbol (aq) tell you about a substance?
Model answer
It is dissolved in water.
- 3
Why is the water made in a neutralisation written H₂O(l) rather than H₂O(aq)?
Model answer
It is the pure liquid itself, not a substance dissolved in water.
- 4
Add state symbols to the reaction of zinc metal with dilute sulfuric acid.
Model answer
Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g).
- 5
Which state symbol shows that a precipitate has formed in a solution?
Model answer
(s), because a precipitate is an insoluble solid.
- 6
Write the equation with state symbols for marble chips reacting with dilute hydrochloric acid.
Model answer
CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g).
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