Global Challenges | OCR GCSE Chemistry A, Higher tier (J248)

Global Challenges

353 questions
22 subtopics
Paper 4
Paper 4

Global Challenges is examined in Chemistry A Paper 4.

It covers extracting metals by reduction and by electrolysis, biological methods of metal extraction, rate against yield in industry, and reaction conditions, the Haber process and fertiliser production, nitrogen, phosphorus and potassium in agriculture, life cycle assessment, recycling, and the decisions behind it, alloys, and the corrosion of metals, comparing glass, ceramics, polymers, composites and metals, functional groups and homologous series, predicting the products of organic reactions, addition polymerisation, condensation polymerisation, and making a polymer, dNA and other natural polymers, fractional distillation of crude oil, the fractions, and crude oil as a feedstock, dependence on hydrocarbons, and cracking, chemical cells and fuel cells, 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.

Sample questions from Global Challenges

Answer each one closed book first, then open the answer.

Extracting metals by reduction and by electrolysis

Give a word equation for the reduction of iron(III) oxide by carbon.

Show the answer
Iron(III) oxide + carbon → iron + carbon dioxide.
Rate against yield in industry, and reaction conditions

Where does the hydrogen used in the Haber process come from?

Show the answer
Mainly from natural gas, by reacting methane with steam.
Life cycle assessment

A plastic bag is buried in landfill and does not break down. Which stage of a life cycle assessment does this belong to?

Show the answer
Disposal at the end of the product's life.
Alloys, and the corrosion of metals

Name three ways of forming a physical barrier on iron to prevent rusting.

Show the answer
Painting it, coating it with oil or grease, and covering it with plastic or another metal.
Predicting the products of organic reactions

Which product is formed when hydrogen adds across the double bond of propene?

Show the answer
Propane, C₃H₈.
Condensation polymerisation, and making a polymer

How is the polymer removed from the beaker once it has begun to form?

Show the answer
It is gripped with tweezers or a glass rod and pulled out steadily as a continuous thread, which is wound onto the rod as more polymer forms behind it.
The fractions, and crude oil as a feedstock

Name the alkane with the formula C₅H₁₂.

Show the answer
Pentane.
Chemical cells and fuel cells

What happens to the hydrogen at the negative electrode of a fuel cell?

Show the answer
It is oxidised, losing electrons which then flow round the external circuit.

The 22 subtopics

One subtopic is one session. Work down the list.

Subtopic	What it covers	Questions
Extracting metals by reduction and by electrolysis	Reduction 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.	16
Biological methods of metal extraction	Bioleaching 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.	10
Rate against yield in industry, and reaction conditions	The Haber and Contact equilibria, how temperature and pressure change yield and rate, the compromise conditions, what a catalyst does to yield, reading rate and yield graphs, and where the nitrogen and hydrogen come from.	21
The Haber process and fertiliser production	What the ammonia from the Haber process is mainly used for, why crops need nitrogen compounds and how cheap fertiliser raises food production, where farmers got nitrogen before, the algal growth that fertiliser run-off causes, preparing ammonium sulfate by titration and crystallisation in the laboratory, and how industrial production differs in scale, acid concentration, automation and continuous running.	16
Nitrogen, phosphorus and potassium in agriculture	The three elements in an NPK fertiliser and what nitrogen, phosphorus and potassium each do for a plant, why fertiliser compounds must be soluble, choosing a fertiliser for a leaf crop, making ammonium nitrate and ammonium sulfate by neutralisation, fertiliser manufacture as a set of integrated processes with its nitric acid, Contact process and raw materials, and crystallising the solid salt.	16
Life cycle assessment	The 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.	16
Recycling, and the decisions behind it	How 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.	16
Alloys, and the corrosion of metals	What an alloy is and why it is harder than the pure metal, the make-up and uses of steel, brass, bronze, solder and duralumin, what corrosion is, the conditions for rusting and the experiment that shows them, why salt speeds it up, why aluminium and copper are protected by their corrosion layers, and preventing rusting with barriers, galvanising and sacrificial protection by zinc or magnesium.	21
Comparing glass, ceramics, polymers, composites and metals	How metals, ceramics, polymers, glass and composites compare in toughness, density, melting point, conductivity and strength, what a composite is, and choosing materials for windows, furnaces, bicycles, cables, kettles and bridges.	16
Functional groups and homologous series	What a homologous series and a functional group are, the general formulae of the alkanes, alkenes, alcohols and carboxylic acids, the C=C and –OH groups, identifying a series from a molecular formula, the first four members of each series, the formulae of propane, but-1-ene and ethanoic acid, and how the atoms in ethene are joined.	16
Predicting the products of organic reactions	The products and equations for the complete combustion of propane and ethanol, adding bromine or hydrogen across the double bond of an alkene and the bromine water test, oxidising alcohols such as ethanol to carboxylic acids, why the functional group decides the reactions of a whole homologous series, and using it to predict the products of unfamiliar compounds.	16
Addition polymerisation	What addition polymerisation, a monomer and a repeating unit are, the C=C double bond a monomer needs and what happens to it, why there is only one product, poly(ethene), poly(propene), poly(chloroethene) and poly(tetrafluoroethene), what n and the end bonds show in a polymer formula, and working out the monomer from a repeating unit.	16
Condensation polymerisation, and making a polymer	What condensation polymerisation is, the two functional groups a monomer needs, the water released at each link, the monomers and links of polyesters and polyamides, and making a polyamide or polyester in the laboratory.	16
DNA and other natural polymers	Nucleotides as the monomers of DNA, its four bases, why DNA counts as a polymer, its double helix shape and its job of carrying genetic instructions, proteins as polymers of amino acids, and starch and cellulose as polymers of glucose.	8
Fractional distillation of crude oil	What 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.	16
The fractions, and crude oil as a feedstock	The 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).	16
Dependence on hydrocarbons, and cracking	Why 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.	18
Chemical cells and fuel cells	What a chemical cell is, why it runs until a reactant is used up and a battery goes flat, the electrolyte and the difference in reactivity that sets the potential difference, making a cell last longer, the hydrogen–oxygen fuel cell with its equation, electrodes and water product, its advantages and disadvantages in cars and spacecraft, and whether a hydrogen car is free of carbon dioxide emissions.	16
The Earth's early atmosphere, and how oxygen developed	The 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.	16
The greenhouse effect, and evidence for climate change	Three 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.	20
Effects of carbon dioxide and methane, and air pollutants	The 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.	20
Producing potable water	What 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.	11

Global Challenges is 353 of the 1,265 questions in the guide.Get the guide, £7

How the guide is worked

Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.

Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.

Read the full method, the return schedule and the research behind it.