Key term
OCR GCSE Combined Science Chemistry J250
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 structures
Global Challenges
Topic overviewExtracting metals by reduction and by electrolysisBiological methods of metal extractionLife 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
Topic overviewMass of solute, concentration and dilution calculationsMeasuring 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
Global Challenges
- 11 subtopics
- 33 things to know
- Paper 10 (Chemistry)
What Global Challenges covers
Global Challenges is examined in Paper 10 (Chemistry). It covers extracting metals by reduction and by electrolysis; biological methods of metal extraction; life cycle assessment; recycling and the decisions behind it; fractional distillation of crude oil; the fractions and crude oil as a feedstock; dependence on hydrocarbons and cracking; the Earth's early atmosphere and how oxygen developed; the greenhouse effect and evidence for climate change; the effects of carbon dioxide and methane, and air pollutants; and producing potable water.
Where it is assessed
Paper 10 (Chemistry)
Combined Science A, Paper 10 (Chemistry): 1 hour 10 minutes, 60 marks, 16.7% of the qualification.
Check the OCR specification ↗The 11 subtopics
Each one has its own page.
- Extracting metals by reduction and by electrolysisReduction by carbon for metals below carbon, the blast furnace and its raw materials, why aluminium needs electrolysis, bauxite and cryolite, the electrodes in aluminium extraction, and the cost of each method.Open →
- Biological methods of metal extractionBioleaching with bacteria and phytoextraction with plants as ways to obtain metals from low-grade ores, how each works, recovering copper from a leachate by displacement with scrap iron or by electrolysis, why the ash is useful, their environmental and economic advantages, their slow rate and toxic leachate as drawbacks, and why these methods are becoming more important.Open →
- Life cycle assessmentThe four stages of a life cycle assessment, placing quarrying, product use, transport and landfill in them, what is measured at each stage, and why comparing two products fairly is difficult.Open →
- Recycling, and the decisions behind itHow plastic bottles become fleece and why that is easier than making new bottles, recycling glass and car tyres for other uses, why recycling aluminium saves so much energy, why sorting comes first and recycled material is often lower grade, the resources saved, and the costs, contamination, scarcity, market prices and social factors that decide whether recycling is worthwhile.Open →
- Fractional distillation of crude oilWhat crude oil is and how fractional distillation separates it in a column that is hot at the bottom and cool at the top, the fractions from refinery gases to bitumen and their uses, why larger hydrocarbons have higher boiling points and condense lower down, which forces are overcome on boiling, and why a fraction boils over a range of temperatures.Open →
- The fractions, and crude oil as a feedstockThe alkanes and their general formula CₙH₂ₙ₊₂, what a hydrocarbon is, working out and naming alkane formulae such as C₈H₁₈ and pentane, what saturated means, why a fraction is not pure, crude oil as the feedstock of the petrochemical industry for polymers, solvents, lubricants and medicines, how crude oil formed, and ethene for poly(ethene).Open →
- Dependence on hydrocarbons, and crackingWhy crude oil is finite and how modern life and transport depend on hydrocarbons, rising costs, arguments against burning oil, uses that do not burn it, pollution concerns, why replacing hydrocarbon fuels is hard, what cracking is and why refineries do it, the conditions for catalytic and steam cracking, its products and equation, and the ethical case against burning oil so quickly.Open →
- The Earth's early atmosphere, and how oxygen developedThe composition of today's atmosphere, the volcanic gases of the early atmosphere, why ideas about it are uncertain and the evidence used, how carbon dioxide dissolved in the oceans and was locked into carbonate rocks and fossil fuels, how photosynthesis slowly produced oxygen and its equation, why oxygen mattered for life, and why nitrogen became the most abundant gas.Open →
- The greenhouse effect, and evidence for climate changeThree greenhouse gases, how the greenhouse effect traps infrared radiation and why life needs it, the effect of more greenhouse gas, the correlation between fossil fuel use and carbon dioxide, ice core evidence, the uncertainty in the evidence and in climate predictions, judging climate claims, peer review, communicating findings, and the ethics of cutting emissions.Open →
- Effects of carbon dioxide and methane, and air pollutantsThe effects of rising carbon dioxide and methane such as warming and rising sea levels, sources of methane, ways to cut emissions including carbon capture and storage and planting trees, why global action is hard, the sources and harm of carbon monoxide, sulfur dioxide, oxides of nitrogen and particulates, and presenting and sampling pollution data with bar charts, histograms and frequency tables.Open →
- Producing potable waterWhat potable water is and how it differs from pure water, treating fresh water by screening, filtering and sterilising with chlorine, ozone or ultraviolet light, desalination by distillation or reverse osmosis and its cost, how hard ground, salt and waste water are to treat, and taking random, representative samples from a reservoir.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Which metals must be extracted by electrolysis, why does that include aluminium, which ore supplies aluminium, and at which electrode does aluminium collect?
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Describe the greenhouse effect.
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Describe how bioleaching obtains copper from a low-grade ore.
Process
Electricity is used to run a washing machine for ten years. Which stage of a life cycle assessment does this belong to?
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What is crude oil?
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What is a hydrocarbon?
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Suggest why replacing hydrocarbon fuels is difficult even though they are finite.
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What is thought to have released the gases that made up the Earth's earliest atmosphere?
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Give two potential effects on the Earth of rising levels of carbon dioxide and methane.
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What is meant by potable water?
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What does the position of a metal relative to carbon in the reactivity series tell you about how it can be extracted?
Process
Describe the stages of phytoextraction.
Process
Lorries carry bottles from the factory to shops across the country. Which stage of a life cycle assessment does this belong to?
Key term
Describe how used plastic bottles can be recycled into fleece fabric.
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Name the fractions obtained from crude oil, from the top of the column downwards.
Numbers
An alkane molecule contains twenty hydrogen atoms. How many carbon atoms does it contain?
Key term
Why do oil refineries crack the longer fractions?
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Which other gases are thought to have been present in the early atmosphere?
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Name three greenhouse gases.
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Why is a rise in sea level a serious risk?
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Explain why potable water is not the same as pure water.
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Why is carbon able to remove the oxygen from iron oxide?
Evaluation
Give one disadvantage of bioleaching linked to the solutions it produces.
Process
A plastic bag is buried in landfill and does not break down. Which stage of a life cycle assessment does this belong to?
Key term
Explain why recycling a drinks bottle into fleece is more viable than recycling it into a new drinks bottle.
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Which fraction leaves at the very top of the fractionating column?
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What is meant by a feedstock?
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Describe the conditions used for catalytic cracking.
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What kinds of evidence do scientists use to work out how the atmosphere has changed?
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What type of radiation does the Earth's surface emit after it has been warmed?
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Give three ways of reducing carbon dioxide emissions.
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Why is water sterilised before it is supplied to homes?
Take Global Challenges further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Bioleaching vs Phytoextraction
Bioleaching: bacteria break down low-grade ore to give a copper leachate. Phytoextraction: plants absorb metal compounds and are burned to a metal-rich ash.
Alkane vs Alkene
Alkane: saturated hydrocarbon with only single bonds, general formula CₙH₂ₙ₊₂. Alkene: hydrocarbon with a carbon–carbon double bond, general formula CₙH₂ₙ.
Questions from this topic
Each one with the model answer underneath.
- 1
What does the position of a metal relative to carbon in the reactivity series tell you about how it can be extracted?
Model answer
A metal less reactive than carbon can be extracted by heating its ore with carbon, while a more reactive metal cannot.
- 2
Why is carbon able to remove the oxygen from iron oxide?
Model answer
Carbon is more reactive than iron, so it takes the oxygen from the iron oxide and is itself oxidised.
- 3
In terms of oxygen, what happens to a metal oxide when it is reduced by carbon?
Model answer
The metal oxide loses its oxygen to the carbon, leaving the metal behind.
- 4
Name the raw materials fed into a blast furnace to extract iron.
Model answer
Iron ore, coke, limestone and hot air.
- 5
Which gas formed inside a blast furnace does most of the reducing of the iron ore?
Model answer
Carbon monoxide.
- 6
Give a word equation for the reduction of iron(III) oxide by carbon.
Model answer
Iron(III) oxide + carbon → iron + carbon dioxide.
What is inside Levo
Six ways to work the same material.
Global Challenges revision questions
- What does Global Challenges cover in OCR GCSE Combined Science Chemistry?
- 11 subtopics: extracting metals by reduction and by electrolysis, biological methods of metal extraction, life cycle assessment, recycling, and the decisions behind it, fractional distillation of crude oil, the fractions, and crude oil as a feedstock, dependence on hydrocarbons, and cracking, the earth's early atmosphere, and how oxygen developed, the greenhouse effect, and evidence for climate change, effects of carbon dioxide and methane, and air pollutants and producing potable water. Each one has its own page with questions and model answers.
- How is Global Challenges organised?
- By the OCR J250 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Global Challenges, 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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