Key term
OCR GCSE Chemistry A J248
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 structuresNanoparticles: size and surface area to volumeUses and risks of nanoparticulate materials
Global Challenges
Topic overviewExtracting metals by reduction and by electrolysisBiological methods of metal extractionRate against yield in industry, and reaction conditionsThe Haber process and fertiliser productionNitrogen, phosphorus and potassium in agricultureLife cycle assessmentRecycling, and the decisions behind itAlloys, and the corrosion of metalsComparing glass, ceramics, polymers, composites and metalsFunctional groups and homologous seriesPredicting the products of organic reactionsAddition polymerisationCondensation polymerisation, and making a polymerDNA and other natural polymersFractional distillation of crude oilThe fractions, and crude oil as a feedstockDependence on hydrocarbons, and crackingChemical cells and fuel cellsThe 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 overviewConcentration in mol/dm³, and titrationTitration calculations, and the mass of a soluteMolar gas volume and the volumes of gasesTheoretical mass and percentage yieldAtom economy, and choosing a reaction pathwayMeasuring 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
Predicting and Identifying Reactions
Topic overviewGroups 1, 7 and 0, and why they behave as they doTransition metalsPredicting reactivity from the Periodic TableReactivity of metals with water and acidsTests for oxygen, hydrogen, carbon dioxide and chlorineTests for aqueous cations and anionsFlame tests, and identifying metal ionsIdentifying a species from test resultsInstrumental methods of analysis
Predicting and Identifying Reactions
- 9 subtopics
- 25 things to know
- Paper 4
What Predicting and Identifying Reactions covers
Predicting and Identifying Reactions is examined in Chemistry A Paper 4. It covers Groups 1, 7 and 0 and why they behave as they do; transition metals; predicting reactivity from the Periodic Table; reactivity of metals with water and acids; the tests for oxygen, hydrogen, carbon dioxide and chlorine; tests for aqueous cations and anions; flame tests and identifying metal ions; identifying a species from test results; and instrumental methods of analysis.
Where it is assessed
Paper 4
Chemistry A Paper 4: 1 hour 45 minutes, 90 marks, 50% of the GCSE.
Check the OCR specification ↗The 9 subtopics
Each one has its own page.
- Groups 1, 7 and 0, and why they behave as they doThe physical properties of the Group 1 metals and their reaction with water, the states, colours and diatomic molecules of chlorine, bromine and iodine, why the noble gases are unreactive and their properties, the outer electrons and ions of Groups 1 and 7, why reactivity rises down Group 1 and falls down Group 7, predictions for rubidium and astatine, halogen displacement, and noble gas boiling points.Open →
- Transition metalsHow transition metals compare with Group 1 metals in melting point, density and reactivity, ions with different charges and the Roman numerals that show them, the colours of copper and iron ions, nickel as the catalyst for margarine, and copper for water pipes.Open →
- Predicting reactivity from the Periodic TableWhere metals and non-metals sit, why a group reacts alike, caesium in water, the formulae of potassium iodide and calcium chloride, chlorine displacing iodine, why argon does not react, and recognising a Group 1 metal.Open →
- Reactivity of metals with water and acidsWhy metals form positive ions when they react with water or acid, the products with acid, why potassium reacts faster than calcium, the metals that react with cold water, magnesium with steam, why copper does not react with acid while zinc and iron react slowly, ordering metals by fair tests and displacement, the temperature rise, cleaning with emery paper, and aluminium's oxide layer.Open →
- Tests for oxygen, hydrogen, carbon dioxide and chlorineThe tests and positive results for oxygen, hydrogen, carbon dioxide and chlorine, why the litmus paper must be damp, what turns limewater milky, telling oxygen from hydrogen with a splint, what chlorine looks and smells like and why it is tested in a fume cupboard, and identifying a gas from its test results.Open →
- Tests for aqueous cations and anionsUsing sodium hydroxide solution to identify calcium, copper(II), iron(II), iron(III) and zinc ions by their precipitates, telling calcium from zinc with excess reagent, the acid test for carbonate ions, acidified silver nitrate for chloride, bromide and iodide ions, the barium chloride test for sulfate ions, and why acid is added first in the halide and sulfate tests.Open →
- Flame tests, and identifying metal ionsThe wire loop and how it is cleaned, the Bunsen flame used and why, picking up a solid sample, why mixtures give unreliable results, and the flame colours of lithium, sodium, potassium, calcium and copper.Open →
- Identifying a species from test resultsWhy a cation test and an anion test are both needed, naming salts from flame colours and precipitates with sodium hydroxide, silver nitrate and barium chloride, and why silver nitrate without acid is unsafe.Open →
- Instrumental methods of analysisThe sensitivity, accuracy and speed of machine methods, their cost and need for trained operators and reference data, why they suit mixtures and tiny samples, and reading a mass spectrum.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
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Describe three features of transition metals: ions of different charges, the colours of copper and iron ion solutions, and coloured compounds.
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Describe the test for sulfate ions, what a positive result looks like, and why the barium chloride is acidified first.
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Predict the formulae of potassium iodide and calcium chloride, and what is seen when chlorine solution is added to sodium iodide solution.
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What two products are formed when a Group 1 metal reacts with water?
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What two products are formed when a metal reacts with a dilute acid?
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Describe the test for oxygen and its positive result.
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Why are two separate tests usually needed to identify an unknown salt?
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Why does the speed of an analytical machine matter in a testing laboratory?
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What are the physical states of chlorine, bromine and iodine at room temperature?
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What is meant by saying that transition metals form ions with different charges? Give an example.
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Where are the metals and the non-metals found in the Periodic Table?
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Explain why potassium reacts far more vigorously with cold water than calcium does.
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Describe the test for hydrogen and its positive result.
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Which reagent is added to a solution to test for calcium, copper, iron and zinc ions?
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What kind of wire is used to hold the sample in a flame test?
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Give two drawbacks of machine methods of analysis.
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What colours are chlorine, bromine and iodine?
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What colours are solutions containing copper(II) ions, iron(II) ions and iron(III) ions?
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Predict the formula of the compound formed between potassium and iodine.
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Name four metals that react noticeably with cold water.
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Describe the test for carbon dioxide and its positive result.
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What is seen when sodium hydroxide solution is added to a solution containing calcium ions?
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Why must the wire be cleaned between one flame test and the next?
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A sample contains several different metal ions. Why would a machine method identify them better than a flame test?
Take Predicting and Identifying Reactions further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Transition metals vs Group 1 metals
Transition metals: hard dense elements of low reactivity that form coloured compounds. Group 1 metals: soft light elements that react vigorously with cold water.
Group 7 vs Group 0
Group 7: reactive non-metals whose atoms gain one electron, forming 1− ions. Group 0: unreactive elements whose atoms already have a full outer shell.
Questions from this topic
Each one with the model answer underneath.
- 1
What are the main physical properties of the metals in Group 1?
Model answer
They are soft enough to cut with a knife, have low densities and low melting points, and are shiny when freshly cut but tarnish quickly in air.
- 2
What two products are formed when a Group 1 metal reacts with water?
Model answer
A metal hydroxide, which dissolves to give an alkaline solution, and hydrogen gas.
- 3
Describe what is observed when a small piece of sodium is dropped onto water.
Model answer
It floats, melts into a ball and fizzes as it moves rapidly across the surface, leaving an alkaline solution behind.
- 4
What are the physical states of chlorine, bromine and iodine at room temperature?
Model answer
Chlorine is a gas, bromine is a liquid and iodine is a solid.
- 5
What colours are chlorine, bromine and iodine?
Model answer
Chlorine is pale green, bromine is red-brown and iodine is a dark grey solid that forms a purple vapour when warmed.
- 6
In what form do the elements of Group 7 exist?
Model answer
As diatomic molecules of two atoms sharing a pair of electrons, such as Cl₂ and Br₂.
What is inside Levo
Six ways to work the same material.
Predicting and Identifying Reactions revision questions
- What does Predicting and Identifying Reactions cover in OCR GCSE Chemistry A?
- 9 subtopics: groups 1, 7 and 0, and why they behave as they do, transition metals, predicting reactivity from the periodic table, reactivity of metals with water and acids, tests for oxygen, hydrogen, carbon dioxide and chlorine, tests for aqueous cations and anions, flame tests, and identifying metal ions, identifying a species from test results and instrumental methods of analysis. Each one has its own page with questions and model answers.
- How is Predicting and Identifying Reactions organised?
- By the OCR J248 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Predicting and Identifying Reactions, on a schedule.
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