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GCSE ChemistryAQA, Edexcel and OCR

Chemical and allied industries: GCSE questions with answers

40 chemistry questions on chemical and allied industries. Pick your answer, then tap to see if you were right and why. Every answer comes from the Show Working science bank, checked against the GCSE content every board in England teaches.

Quiz yourself: 40 questions 5 6-mark questions

01 / Quiz yourselfTry it, then tap to check

Chemical and allied industries questions to try

Choose your answer before you open it. Then read why, so it sticks.

01 / Chemical and allied industriesBoth tiers

What does a life cycle assessment (LCA) of a product measure?

  1. AOnly the cost of making it
  2. BHow many people buy it and how often they use it
  3. CIts environmental impact at each stage of its life
  4. DHow long it lasts before it breaks
Show the answer

Answer: C Its environmental impact at each stage of its life

A life cycle assessment looks at the environmental impact of a product at every stage: getting and processing the raw materials, making and packaging it, using it, and disposing of it at the end. Transport between the stages is counted too.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.2.1 Life cycle assessment

02 / Chemical and allied industriesBoth tiers

Which of these is hardest to give a fair number to in an LCA?

  1. AThe mass of waste produced
  2. BThe volume of water used
  3. CThe energy used in making it
  4. DThe harm caused by a pollutant
Show the answer

Answer: D The harm caused by a pollutant

Water, energy, resources and waste can be measured fairly easily, but putting a number on the harm a pollutant does needs value judgements. Selective or shortened LCAs can be used to reach a conclusion decided in advance, for example in an advert.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.2.1 Life cycle assessment

03 / Chemical and allied industriesBoth tiers

Bag A takes 1.6 MJ of energy to make and gives 0.05 kg of waste. Bag B takes 0.6 MJ and gives 0.01 kg. Each is used once. Which is better for the environment on this data?

  1. AThey are the same
  2. BBag A
  3. CBag B
  4. DYou need the price to decide
Show the answer

Answer: C Bag B

To compare products with LCA data, compare the same measures, such as energy, water and waste, for the same use. A product that costs more to make can still have a lower impact overall if it is reused many times instead of being replaced.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.2.1 Life cycle assessment

04 / Chemical and allied industriesBoth tiers

How are glass bottles recycled into different glass products?

  1. AThey are dissolved in acid
  2. BThey are burned in a furnace for energy
  3. CThey are electrolysed
  4. DThey are crushed and melted
Show the answer

Answer: D They are crushed and melted

Glass bottles can be reused, or crushed and melted to make different glass products. Metals are recycled by melting them and recasting or reforming them into new products. Plastic drinks bottles can be turned into fibres for clothing.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.2.2 Ways of reducing the use of resources

05 / Chemical and allied industriesBoth tiers

Why is recycling aluminium cans worthwhile?

  1. AAluminium ore will never run out
  2. BRecycled aluminium is a different element
  3. CIt saves energy compared with extraction
  4. DIt needs more energy than extracting it
Show the answer

Answer: C It saves energy compared with extraction

Recycling is viable when it saves more than it costs. Recycling metals uses less energy than extracting them from ores, makes finite ores last longer, means less mining and quarrying, and sends less waste to landfill.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.2.2 Ways of reducing the use of resources

06 / Chemical and allied industriesBoth tiers

Which makes recycling a material less worthwhile?

  1. AIt is easy to collect and sort
  2. BIt is hard to separate from other materials
  3. CIt is valuable and in short supply
  4. DIt saves energy compared with new material
Show the answer

Answer: B It is hard to separate from other materials

Whether recycling is worthwhile depends on the energy and cost of collecting, transporting and sorting the waste, how hard the materials are to separate, how much material there is, how valuable it is, and the cost and impact of making it new instead.

Checked against OCR Twenty First Century Chemistry B (J258) specification, C4.5.7 decisions on recycling

07 / Chemical and allied industriesBoth tiers

In the fractionating column, where do the fractions with the highest boiling points condense?

  1. ANear the top
  2. BThey leave the top as gases
  3. CNear the bottom
  4. DIn the middle
Show the answer

Answer: C Near the bottom

Crude oil is heated so most of it turns to vapour, which rises up a column that is hot at the bottom and cooler at the top. Large molecules with high boiling points condense near the bottom; smaller ones rise higher, and the smallest leave the top as gases.

Checked against AQA GCSE Chemistry (8462) specification, 4.7.1.2 Fractional distillation and petrochemicals

08 / Chemical and allied industriesBoth tiers

Compared with a fraction from the top of the column, a fraction from near the bottom has:

  1. Alonger molecules and a higher boiling point
  2. Blonger molecules and a lower boiling point
  3. Cshorter molecules and a higher boiling point
  4. Dshorter molecules and a lower boiling point
Show the answer

Answer: A longer molecules and a higher boiling point

As hydrocarbon molecules get longer, the boiling point and viscosity go up and the hydrocarbon gets harder to ignite. So fractions from the top of the column, with short molecules, are runny and flammable, and those from the bottom are thick and hard to set alight.

Checked against AQA GCSE Chemistry (8462) specification, 4.7.1.3 Properties of hydrocarbons

09 / Chemical and allied industriesBoth tiers

The alkanes have the general formula CₙH₂ₙ₊₂. How many hydrogen atoms are in an alkane with 5 carbon atoms?

  1. A8
  2. B10
  3. C11
  4. D12
Show the answer

Answer: D 12

Most compounds in crude oil fractions are alkanes, a homologous series with the general formula CₙH₂ₙ₊₂. For example, propane has three carbon atoms and 2 × 3 + 2 = 8 hydrogen atoms, so its formula is C₃H₈.

Checked against AQA GCSE Chemistry (8462) specification, 4.7.1.1 Crude oil, hydrocarbons and alkanes

10 / Chemical and allied industriesBoth tiers

What is a hydrocarbon?

  1. AA compound of hydrogen and carbon only
  2. BA mixture of hydrogen and carbon atoms
  3. CA compound of hydrogen, carbon and oxygen
  4. DAny compound that burns in air
Show the answer

Answer: A A compound of hydrogen and carbon only

A hydrocarbon is a compound of hydrogen and carbon only. Alkanes are a homologous series: they share a general formula, have similar chemical properties and each differs from the next by CH₂. They are saturated because they have only single bonds between carbon atoms.

Checked against OpenStax Chemistry 2e, 20.1 Hydrocarbons

11 / Chemical and allied industriesBoth tiers

What does cracking do?

  1. ARemoves the sulfur impurities from crude oil
  2. BBreaks large hydrocarbons into smaller ones
  3. CJoins small hydrocarbons into larger ones
  4. DSeparates crude oil into its fractions
Show the answer

Answer: B Breaks large hydrocarbons into smaller ones

Cracking breaks large alkane molecules into smaller, more useful ones. The products are a shorter alkane and at least one alkene, for example C₁₀H₂₂ → C₈H₁₈ + C₂H₄. It is a thermal decomposition reaction.

Checked against AQA GCSE Chemistry (8462) specification, 4.7.1.4 Cracking and alkenes

12 / Chemical and allied industriesBoth tiers

Why is cracking needed?

  1. ACrude oil has too many short molecules
  2. BShort molecules cannot be used as fuels
  3. CLong molecules burn too easily in engines
  4. DCrude oil has too few short molecules for demand
Show the answer

Answer: D Crude oil has too few short molecules for demand

Crude oil contains more long-chain hydrocarbons than are needed and too few short ones for fuels such as petrol, so long ones are cracked. Cracking needs heat and either a hot catalyst or steam at a very high temperature. The alkenes made are used to make polymers.

Checked against AQA GCSE Chemistry (8462) specification, 4.7.1.4 Cracking and alkenes

13 / Chemical and allied industriesBoth tiers

What happens when an alkene is shaken with bromine water?

  1. AThe bromine water turns blue
  2. BA white precipitate forms in the water
  3. CThe bromine water turns milky
  4. DThe bromine water turns colourless
Show the answer

Answer: D The bromine water turns colourless

Alkenes have a carbon-carbon double bond, so they react with bromine. Shaking an alkene with orange bromine water turns it colourless, while an alkane leaves it orange. This shows that cracking has made an alkene.

Checked against AQA GCSE Chemistry (8462) specification, 4.7.1.4 Cracking and alkenes

14 / Chemical and allied industriesBoth tiers

Which metals can be extracted by heating their oxides with carbon?

  1. AMetals less reactive than carbon
  2. BEvery metal there is
  3. COnly the metals in Group 1
  4. DMetals more reactive than carbon
Show the answer

Answer: A Metals less reactive than carbon

Carbon can remove oxygen from the oxide of a metal that is less reactive than carbon, such as iron, zinc or copper. Metals more reactive than carbon, such as aluminium, cannot be extracted this way.

Checked against AQA GCSE Chemistry (8462) specification, 4.4.1.3 Extraction of metals and reduction

15 / Chemical and allied industriesBoth tiers

When zinc oxide is heated with carbon to make zinc, what happens to the zinc oxide?

  1. AIt is electrolysed
  2. BIt is oxidised
  3. CIt is neutralised
  4. DIt is reduced
Show the answer

Answer: D It is reduced

Reduction is the loss of oxygen. When a metal oxide is heated with carbon, the metal oxide is reduced to the metal and the carbon gains oxygen, so it is oxidised. Zinc is a non-ferrous metal (not iron) that can be extracted this way.

Checked against OCR Twenty First Century Chemistry B (J258) specification, C3.2.4 extraction of metals using carbon

16 / Chemical and allied industriesBoth tiers

Why is gold found in the ground as the metal itself?

  1. AIt is very unreactive
  2. BIt is more reactive than carbon
  3. CIt is very reactive
  4. DIt has a low density
Show the answer

Answer: A It is very unreactive

Very unreactive metals such as gold are found in the Earth as the metal itself, not as compounds. Most metals are found as compounds in ores, and the more reactive the metal, the harder and costlier it is to extract.

Checked against AQA GCSE Chemistry (8462) specification, 4.4.1.3 Extraction of metals and reduction

17 / Chemical and allied industriesBoth tiers

Why is aluminium extracted by electrolysis rather than by heating with carbon?

  1. AAluminium is less reactive than carbon
  2. BElectrolysis is cheaper than carbon
  3. CAluminium oxide dissolves in water
  4. DAluminium is more reactive than carbon
Show the answer

Answer: D Aluminium is more reactive than carbon

Metals more reactive than carbon, such as aluminium, cannot be reduced by carbon, so they are extracted by electrolysis of a molten compound. This is expensive because large amounts of energy are needed to melt the compound and to produce the electric current.

Checked against AQA GCSE Chemistry (8462) specification, 4.4.3.3 Using electrolysis to extract metals

18 / Chemical and allied industriesBoth tiers

In the electrolysis of molten aluminium oxide, where is aluminium formed?

  1. AAt both electrodes
  2. BIn the air above the cell
  3. CAt the negative electrode
  4. DAt the positive electrode
Show the answer

Answer: C At the negative electrode

In electrolysis the ionic compound must be molten or dissolved so its ions can move. Positive aluminium ions move to the negative electrode, where they gain electrons and form aluminium. Oxide ions move to the positive electrode and form oxygen.

Checked against AQA GCSE Chemistry (8462) specification, 4.4.3.3 Using electrolysis to extract metals

19 / Chemical and allied industriesHigher only

When plants are used to extract a metal, what happens to them after they are harvested?

  1. AThey are replanted in richer soil
  2. BThey are burned and the ash is used
  3. CThey are fermented to make ethanol
  4. DThey are buried in landfill
Show the answer

Answer: B They are burned and the ash is used

In phytomining, or phytoextraction, plants grown on soil containing a metal absorb its compounds. The plants are harvested and burned, and the ash contains metal compounds. The metal is then extracted, for example by electrolysis or by displacement with scrap iron.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.1.4 Alternative methods of extracting metals

20 / Chemical and allied industriesHigher only

When bacteria are used to extract copper, what do the bacteria produce?

  1. ALumps of pure copper metal
  2. BCopper oxide powder
  3. CA gas that contains copper atoms
  4. DA solution containing copper compounds
Show the answer

Answer: D A solution containing copper compounds

Bacteria can produce a solution, called a leachate, containing metal compounds from low-grade ore. Copper is then extracted from the solution, for example by displacement with scrap iron or by electrolysis. These methods are used because high-grade copper ores are scarce.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.1.4 Alternative methods of extracting metals

21 / Chemical and allied industriesHigher only

Which is an advantage of biological methods of metal extraction?

  1. AThey produce pure metal directly
  2. BThey need very high temperatures
  3. CThey can use low-grade ores and waste
  4. DThey are very fast
Show the answer

Answer: C They can use low-grade ores and waste

Biological methods avoid the digging, moving and disposal of large amounts of rock that traditional mining needs, use less energy and can use low-grade ores and waste. Their main drawback is that they are slow.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.1.4 Alternative methods of extracting metals

22 / Chemical and allied industriesBoth tiers · separate only

What is corrosion?

  1. AA metal reacting with substances around it
  2. BA metal being worn away by rubbing
  3. CA metal melting in hot weather
  4. DA metal changing from solid to liquid
Show the answer

Answer: A A metal reacting with substances around it

Corrosion is the destruction of a material by chemical reactions with substances in its surroundings. Rusting is the corrosion of iron and needs both oxygen (from air) and water. Nails in dry air, or in boiled water under a layer of oil, do not rust.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.3.1 Corrosion and its prevention

23 / Chemical and allied industriesBoth tiers · separate only

Rusting is an example of which kind of reaction?

  1. AOxidation
  2. BThermal decomposition
  3. CReduction
  4. DNeutralisation
Show the answer

Answer: A Oxidation

In rusting, iron reacts with oxygen and water to form hydrated iron(III) oxide. The iron gains oxygen, so it is oxidised. A rusting nail gets heavier, because atoms from the air and water join it.

Checked against OpenStax Chemistry 2e, 17.6 Corrosion

24 / Chemical and allied industriesBoth tiers · separate only

How does painting stop iron from rusting?

  1. AIt corrodes instead of the iron
  2. BIt makes the iron more reactive
  3. CIt turns the iron into an alloy
  4. DIt keeps out oxygen and water
Show the answer

Answer: D It keeps out oxygen and water

Painting, greasing, oiling, coating with plastic and electroplating all put a barrier between the iron and the oxygen and water it needs to rust. If the barrier is scratched, the iron underneath can start to rust.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.3.1 Corrosion and its prevention

25 / Chemical and allied industriesBoth tiers · separate only

Why does a block of zinc bolted to a steel hull stop the hull rusting?

  1. AZinc is more reactive, so it corrodes instead
  2. BZinc is less reactive, so it corrodes instead
  3. CZinc keeps water away from the hull
  4. DZinc turns the steel into a stronger alloy
Show the answer

Answer: A Zinc is more reactive, so it corrodes instead

In sacrificial protection a more reactive metal, such as zinc or magnesium, is attached to iron. The more reactive metal loses electrons and corrodes instead of the iron. Galvanised iron has a zinc coating, so it is still protected when scratched.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.3.1 Corrosion and its prevention

26 / Chemical and allied industriesBoth tiers · separate only

Aluminium is quite reactive, yet aluminium window frames do not corrode away. Why?

  1. AAluminium is less reactive than gold
  2. BAluminium does not react with oxygen
  3. CRain washes the oxygen away
  4. DA thin oxide layer protects the metal
Show the answer

Answer: D A thin oxide layer protects the metal

Aluminium reacts with oxygen to form a thin, tough layer of aluminium oxide on its surface. This layer stops air and water reaching the metal underneath, so the aluminium does not corrode any further.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.3.1 Corrosion and its prevention

27 / Chemical and allied industriesBoth tiers · separate only

Why is an alloy usually harder than the pure metal?

  1. ADifferent-sized atoms stop layers sliding easily
  2. BThe atoms in an alloy are all exactly the same size
  3. CThe bonds in an alloy are covalent
  4. DAn alloy has no delocalised electrons
Show the answer

Answer: A Different-sized atoms stop layers sliding easily

An alloy is a mixture of a metal with one or more other elements, usually other metals. Atoms of different sizes distort the regular layers, so it is harder for the layers to slide over each other. This makes most alloys harder than the pure metal.

Checked against Pearson Edexcel GCSE Chemistry (1CH0) specification, 5.5C alloys and strength

28 / Chemical and allied industriesBoth tiers · separate only

What are steels?

  1. AAlloys of copper and zinc
  2. BAlloys of iron with carbon
  3. CAlloys of copper and tin
  4. DPure iron with no carbon
Show the answer

Answer: B Alloys of iron with carbon

Steels are alloys of iron with carbon, and often with other metals. Adding chromium and nickel makes stainless steel, which is hard and resists corrosion, so it is used for cutlery and sinks.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.3.2 Alloys as useful materials

29 / Chemical and allied industriesBoth tiers · separate only

How does high carbon steel compare with low carbon steel?

  1. AIt rusts much less easily
  2. BIt is stronger but more brittle
  3. CIt is weaker and more flexible
  4. DIt is softer and more easily shaped
Show the answer

Answer: B It is stronger but more brittle

The amount of carbon changes the properties of steel. High carbon steel is strong but brittle, so it suits cutting tools. Low carbon steel is softer and more easily shaped, so it suits car bodies and wire.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.3.2 Alloys as useful materials

30 / Chemical and allied industriesBoth tiers · separate only

Brass is an alloy of copper and which other metal?

  1. ATin
  2. BIron
  3. CLead
  4. DZinc
Show the answer

Answer: D Zinc

Brass is an alloy of copper and zinc. It is harder than pure copper and resists corrosion, so it is used for things like door fittings, taps and musical instruments.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.3.2 Alloys as useful materials

31 / Chemical and allied industriesBoth tiers · separate only

Why are aluminium alloys used to build aircraft?

  1. AThey are heavy and very soft
  2. BThey conduct heat very poorly
  3. CThey are strong and have a low density
  4. DThey are brittle but very cheap to make
Show the answer

Answer: C They are strong and have a low density

Aluminium alloys have a low density and are much stronger than pure aluminium, so they are used where strength and light weight both matter, such as in aircraft and bicycle frames.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.3.2 Alloys as useful materials

32 / Chemical and allied industriesBoth tiers · separate only

Which set of properties is typical of glass and clay ceramics?

  1. ASoft, flexible and good conductors
  2. BMalleable, ductile and good conductors
  3. CHard, brittle and electrical insulators
  4. DLow melting point and very flexible
Show the answer

Answer: C Hard, brittle and electrical insulators

Glass and clay ceramics are hard and stiff but brittle, have high melting points and do not conduct electricity. Clay ceramics such as bricks and pottery are made by shaping wet clay and then heating it in a furnace.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.3.3 Ceramics, polymers and composites

33 / Chemical and allied industriesBoth tiers · separate only

What is a composite material made of?

  1. ATwo metals melted together
  2. BA reinforcement held together in a matrix
  3. CLong chains of one monomer
  4. DA single pure element
Show the answer

Answer: B A reinforcement held together in a matrix

Most composites are made of two materials: fibres or fragments of a reinforcement, held together by a matrix or binder. Examples are fibreglass, carbon fibre reinforced polymer, reinforced concrete and wood. They combine useful properties, such as being strong but light.

Checked against AQA GCSE Chemistry (8462) specification, 4.10.3.3 Ceramics, polymers and composites

34 / Chemical and allied industriesBoth tiers · separate only

Which set of properties is typical of most metals?

  1. ALow density, insulating and flexible
  2. BGood conductors, malleable and strong
  3. CBrittle, insulating and transparent
  4. DHard, brittle and insulating
Show the answer

Answer: B Good conductors, malleable and strong

Metals conduct heat and electricity, are strong and can be hammered into shape (malleable). Polymers usually have a low density, are flexible and are insulators, but many soften at fairly low temperatures.

Checked against OCR Twenty First Century Chemistry B (J258) specification, C4.1.1 properties of materials

35 / Chemical and allied industriesBoth tiers · separate only

Material Y has a density of 7.9 g/cm³, conducts electricity and can be hammered into shape. What type of material is it?

  1. AA glass
  2. BA metal
  3. CA clay ceramic
  4. DA polymer
Show the answer

Answer: B A metal

Data on density, melting point, conductivity, strength and brittleness let you sort materials. Metals conduct and can be shaped; polymers have low densities and low melting or softening points; glass and clay ceramics are hard, brittle insulators with high melting points.

Checked against OCR Twenty First Century Chemistry B (J258) specification, C4.1.1 properties of materials

36 / Chemical and allied industriesBoth tiers · separate only

Which property makes copper a good choice for electrical wires?

  1. AIt is a good electrical conductor
  2. BIt has a very low density
  3. CIt is a good insulator
  4. DIt is brittle
Show the answer

Answer: A It is a good electrical conductor

Choose a material by matching its properties to the job. Copper conducts electricity well, so it is used for wires, and a flexible polymer coating insulates them. Glass is transparent and withstands heat, so it suits an oven door.

Checked against Pearson Edexcel GCSE Chemistry (1CH0) specification, 9.39C properties and uses of materials

37 / Chemical and allied industriesBoth tiers · separate only

A wind turbine blade must be long, strong and light. Which material is best?

  1. ASoda-lime glass
  2. BA fibre-reinforced composite
  3. CLead
  4. DClay ceramic
Show the answer

Answer: B A fibre-reinforced composite

Composites such as glass or carbon fibre reinforced polymers are strong but light, so they suit turbine blades, boats and racing bikes. Clay ceramics are hard and strong when squashed (in compression), so bricks can carry the weight of a wall.

Checked against Pearson Edexcel GCSE Chemistry (1CH0) specification, 9.39C properties and uses of materials

38 / Chemical and allied industriesHigher only · separate only

A graph shows the rate of a reaction against temperature. What does it usually show?

  1. AThe rate falls as the temperature rises
  2. BThe rate rises as the temperature rises
  3. CThe rate stays the same at all temperatures
  4. DThe rate is zero above room temperature
Show the answer

Answer: B The rate rises as the temperature rises

Graphs of rate against conditions show that a higher temperature, a higher pressure for gases, a higher concentration or a catalyst make a reaction faster. Higher pressure and concentration make collisions more frequent; a higher temperature also makes more collisions energetic enough to react.

Checked against OCR Gateway Chemistry A (J248) specification, C6.1e graphs of reaction conditions versus rate

39 / Chemical and allied industriesHigher only · separate only

A forward reaction is exothermic. What does a lower temperature do?

  1. ARaises the yield and speeds up the rate
  2. BLowers the yield and slows the rate
  3. CRaises the yield but slows the rate
  4. DLowers the yield but speeds up the rate
Show the answer

Answer: C Raises the yield but slows the rate

For an exothermic forward reaction, a lower temperature gives a higher equilibrium yield but a slower rate. Industry uses a compromise temperature that gives an acceptable yield in an acceptable time. A catalyst speeds up both directions, so equilibrium is reached sooner without changing the yield.

Checked against OpenStax Chemistry 2e, 13.3 Shifting Equilibria: Le Châtelier’s Principle

40 / Chemical and allied industriesHigher only · separate only

In N₂ + 3H₂ ⇌ 2NH₃, why does a higher pressure increase the yield of ammonia?

  1. AThe forward reaction is endothermic
  2. BThere are fewer gas molecules on the right
  3. CThere are more gas molecules on the right
  4. DPressure makes the catalyst work
Show the answer

Answer: B There are fewer gas molecules on the right

Four molecules of gas react to make two, so a higher pressure moves the equilibrium towards ammonia and also speeds up the reaction. But very high pressures need a lot of energy and strong, expensive equipment, and are more dangerous, so a compromise pressure is used.

Checked against OpenStax Chemistry 2e, 13.3 Shifting Equilibria: Le Châtelier’s Principle

02 / Longer answersMarked by levels

6-mark questions on this topic

Write your answer first, on paper. Then open it and tick off the points you made. How 6-mark questions are marked.

6 marks / Extracting iron and aluminiumBoth tiers

Iron is extracted from iron oxide by heating it with carbon. Aluminium is extracted from aluminium oxide by electrolysis.

Explain why these two metals are extracted in different ways.

What a full answer includes
  • The method used depends on where the metal is in the reactivity series compared with carbon.
  • Iron is less reactive than carbon, so carbon can remove the oxygen from iron oxide.
  • The iron oxide is reduced (loses oxygen) and the carbon is oxidised to carbon dioxide.
  • Aluminium is more reactive than carbon, so carbon cannot reduce aluminium oxide.
  • So aluminium is extracted by electrolysis of molten aluminium oxide, and aluminium forms at the negative electrode.
  • The aluminium oxide is dissolved in molten cryolite to lower the temperature needed.
  • Electrolysis uses large amounts of electricity and energy to melt the ore, so it is more expensive than reduction with carbon.

Model answer

Most metals are found in the Earth as compounds, such as oxides, and the way a metal is extracted depends on its position in the reactivity series compared with carbon. Iron is less reactive than carbon. This means that when iron oxide is heated with carbon, the carbon takes the oxygen away from the iron oxide. The iron oxide is reduced, because it loses oxygen, to form iron, and the carbon is oxidised to carbon dioxide. This is a relatively cheap method because carbon is cheap. Aluminium is more reactive than carbon, so carbon cannot remove the oxygen from aluminium oxide, and heating it with carbon would not work. Instead aluminium is extracted by electrolysis. The aluminium oxide is melted so that its ions can move; it is dissolved in molten cryolite, which lowers the temperature needed and saves energy. Aluminium ions move to the negative electrode, where aluminium metal forms. Electrolysis needs a very large amount of electricity, as well as energy to keep the mixture molten, so it is much more expensive than reduction with carbon and is only used when it has to be.

Where marks slip

Saying aluminium “is too reactive to be extracted” is not enough; say it is more reactive than carbon, so carbon cannot reduce it. Cryolite lowers the working temperature; it does not raise it.

6 marks / Fractional distillation of crude oilBoth tiers

Describe and explain how crude oil is separated into fractions by fractional distillation.

What a full answer includes
  • Crude oil is a mixture of hydrocarbons with different boiling points.
  • The crude oil is heated until most of it evaporates.
  • The vapours enter a fractionating column that is hot at the bottom and cooler at the top.
  • The vapours rise up the column and cool down.
  • Each hydrocarbon condenses when it reaches a level that is below its boiling point, and is collected there.
  • Larger molecules have higher boiling points, because their intermolecular forces are stronger, so they condense near the bottom.
  • Smaller molecules have lower boiling points, so they rise higher before condensing or leave the top as gases.
  • Each fraction is a mixture of hydrocarbons with similar numbers of carbon atoms and similar boiling points.

Model answer

Crude oil is a mixture of many hydrocarbons, mostly alkanes, whose molecules are different sizes and so have different boiling points. In fractional distillation the crude oil is heated until most of it evaporates, and the vapours are passed into the bottom of a tall fractionating column. The column has a temperature gradient: it is very hot at the bottom and gets cooler towards the top. As the vapours rise up the column they cool. When a hydrocarbon reaches a level where the temperature is below its boiling point, it condenses to a liquid and is collected on trays at that level. Hydrocarbons with large molecules have stronger intermolecular forces and higher boiling points, so they condense low down and are collected near the bottom, as fractions such as fuel oil and bitumen. Hydrocarbons with small molecules have weaker intermolecular forces and lower boiling points, so they rise further before condensing, giving fractions such as petrol near the top, while the smallest molecules leave the top as gases. Each fraction is a mixture of hydrocarbons with a similar number of carbon atoms and similar boiling points.

Where marks slip

Answers that separate by melting point, or say the column is hottest at the top, lose marks. It is boiling points, and the column is hottest at the bottom.

6 marks / Cracking and why it is neededBoth tiers

Fractional distillation of crude oil gives more of the long-chain fractions, such as fuel oil, than people need, and less petrol than people need.

Describe how long-chain hydrocarbons are cracked and explain why cracking is useful.

What a full answer includes
  • Cracking breaks long-chain alkanes into shorter, more useful molecules.
  • The long-chain hydrocarbons are heated to turn them into vapour.
  • In catalytic cracking the vapour is passed over a hot catalyst.
  • In steam cracking the vapour is mixed with steam and heated to a very high temperature.
  • The products are shorter alkanes and alkenes, for example C₁₀H₂₂ → C₈H₁₈ + C₂H₄.
  • There is more demand for short-chain fuels such as petrol than crude oil supplies, so cracking matches supply to demand.
  • Shorter alkanes are useful fuels because they ignite more easily.
  • Alkenes are used to make polymers and as starting materials for other chemicals.

Model answer

Cracking breaks down long-chain alkanes, which are not very useful, into shorter molecules that are more useful. First the long-chain hydrocarbons are heated so that they vaporise. In catalytic cracking the hot vapour is passed over a hot catalyst, which breaks the molecules up. In steam cracking the vapour is mixed with steam and heated to a very high temperature instead. Cracking is a thermal decomposition, and the products are a mixture of shorter alkanes and alkenes. For example, decane can be cracked to give octane and ethene: C₁₀H₂₂ → C₈H₁₈ + C₂H₄. Cracking is useful because fractional distillation produces more of the long-chain fractions than people need, but not enough of the short-chain fractions such as petrol, which are in high demand as fuels. Cracking turns the surplus long chains into shorter alkanes that are good fuels, because they are less viscous and ignite more easily. It also makes alkenes, such as ethene, which are more reactive than alkanes and are used to make polymers like poly(ethene) and as starting materials for many other chemicals.

Where marks slip

Saying cracking makes “smaller molecules” without saying why they are more useful (fuels, alkenes for polymers) stays in the lower levels. Remember the products include alkenes, not just alkanes.

6 marks / Life cycle of shopping bagsBoth tiers

A shop is choosing between paper bags and poly(ethene) bags. This is what its supplier claims (the figures are made up for this question): a paper bag is made from wood, uses about three times as much energy and much more water to make, is heavier to transport, and is usually used once, but it can be recycled and rots away. A poly(ethene) bag is made from crude oil, can be reused many times, and lasts for hundreds of years in landfill if thrown away.

Evaluate which bag the shop should choose, using the stages of a life cycle assessment.

What a full answer includes
  • A life cycle assessment looks at the environmental impact at every stage: raw materials, manufacture, use and disposal.
  • Raw materials: wood is renewable, but crude oil is a finite resource.
  • Manufacture: the paper bag uses more energy and water, so more fuel is burned and more carbon dioxide may be released.
  • Use: the paper bag is heavier, so transporting it uses more fuel, and it is used only once.
  • Use: the poly(ethene) bag can be reused many times, so fewer bags are needed.
  • Disposal: paper rots away or is recycled, but poly(ethene) is not biodegradable, so it fills landfill or becomes litter.
  • Some effects, such as the harm from litter, are hard to give a number to, so they rely on judgement.
  • A justified conclusion.

Model answer

A life cycle assessment compares the environmental impact of the two bags at each stage of their lives: getting the raw materials, making them, using them and disposing of them. For raw materials, paper comes from wood, which is renewable if trees are replanted, but poly(ethene) comes from crude oil, which is a finite resource. For manufacture, the supplier claims the paper bag needs about three times as much energy and much more water, so more fuel is likely to be burned and more carbon dioxide released. During use, paper bags are heavier, so more fuel is used to transport them, and they are normally used only once, whereas a poly(ethene) bag can be reused many times, so far fewer bags are needed. At disposal, paper bags rot away or can be recycled, while poly(ethene) is not biodegradable and can last in landfill for centuries or end up as litter that harms wildlife. Some of these impacts, like the harm from litter, are hard to measure with numbers. Overall, I think the poly(ethene) bag is better, as long as customers reuse it many times, because it uses much less energy per use.

Where marks slip

Answers that copy out the information without comparing the stages, or that give no final judgement, cannot reach the top level. Link each fact to a stage and finish with a reasoned choice.

6 marks / Extracting copper with plants and bacteriaHigher only

High-grade copper ores are running out. Mining companies are looking at phytomining and bioleaching to get copper from low-grade ores, which contain only a small percentage of copper.

Evaluate the use of phytomining and bioleaching to extract copper.

What a full answer includes
  • Phytomining: plants grown on low-grade ore absorb copper compounds, then are harvested and burned, and the ash contains copper compounds.
  • Bioleaching: bacteria produce a leachate solution that contains copper compounds.
  • The copper is then obtained from the compounds, for example by displacement with scrap iron or by electrolysis.
  • Both can extract copper from low-grade ores that would not be worth mining in the usual way.
  • They avoid digging up, moving and dumping large amounts of rock, so there is less damage to the landscape.
  • They need less energy than traditional mining and smelting.
  • Both are slow: plants take time to grow, and bacteria work slowly.
  • The leachate from bioleaching can be toxic and could pollute water if it escapes.
  • A justified conclusion.

Model answer

In phytomining, plants are grown on soil containing low-grade copper ore. The plants absorb copper compounds through their roots and build them up in their tissues. The plants are then harvested and burned, and the ash contains copper compounds. In bioleaching, bacteria are used to produce a leachate, a solution that contains copper compounds. In both cases the copper can then be obtained from its compounds, for example by displacement using scrap iron or by electrolysis. The main advantage is that both methods can get copper from low-grade ores, and even from old mine waste, which would not be worth extracting by traditional methods, so they help to conserve scarce high-grade ores. They also avoid digging up, moving and dumping huge amounts of rock, so they cause less damage to the landscape and need less energy than traditional mining and smelting. However, both methods are slow, because plants take months to grow and bacteria work slowly, and phytomining needs a large area of land. The leachate from bioleaching may be toxic and could pollute rivers if it leaks. Overall, they are worthwhile for low-grade ores, but are too slow to replace traditional mining completely.

Where marks slip

Pupils often mix up the two methods: phytomining uses plants and bioleaching uses bacteria. An evaluation also needs disadvantages and a conclusion, not only advantages.

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