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
Predicting and Identifying Reactions
- 4 subtopics
- 12 things to know
- Paper 4 (Chemistry)
What Predicting and Identifying Reactions covers
Predicting and Identifying Reactions is examined in Paper 4 (Chemistry), except the tests for oxygen, hydrogen, carbon dioxide and chlorine, which the specification places in Topic C3 and examines in Paper 3 (Chemistry). It covers Groups 1, 7 and 0 and why they behave as they do; predicting reactivity from the Periodic Table; reactivity of metals with water and acids; and the tests for oxygen, hydrogen, carbon dioxide and chlorine.
Where it is assessed
Paper 4 (Chemistry)
Combined Science A, Paper 4 (Chemistry): 1 hour 10 minutes, 60 marks, 16.7% of the qualification.
Check the OCR specification ↗The 4 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 →
- 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 →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Where are metals and non-metals in the Periodic Table, and what formulae form between potassium and iodine, and between calcium and chlorine?
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Give the states and colours of chlorine, bromine and iodine at room temperature, and the form in which Group 7 elements exist.
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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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What two products are formed when a Group 1 metal reacts with water?
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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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What are the physical states of chlorine, bromine and iodine at room temperature?
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Where are the metals and the non-metals found in the Periodic Table?
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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.
Take Predicting and Identifying Reactions further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
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 Combined Science Chemistry?
- 4 subtopics: groups 1, 7 and 0, and why they behave as they do, predicting reactivity from the periodic table, reactivity of metals with water and acids and tests for oxygen, hydrogen, carbon dioxide and chlorine. Each one has its own page with questions and model answers.
- How is Predicting and Identifying Reactions organised?
- By the OCR J250 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Predicting and Identifying Reactions, on a schedule.
Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.
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