1. 1
   An oil refinery heats a sample of the long-chain alkane decane (C10H22) with a hot catalyst, cracking it to produce a mixture of two smaller hydrocarbon molecules: octane (C8H18) and ethene (C2H4).

   (a)

   Which statement correctly describes what type of hydrocarbons octane and ethene are?

   [1 mark]

   • AOctane is a saturated alkane; ethene is an unsaturated alkene
   • BBoth octane and ethene are unsaturated alkenes
   • CBoth octane and ethene are saturated alkanes
   • DOctane is an unsaturated alkene; ethene is a saturated alkane

   (b)

   Why is cracking carried out on long-chain hydrocarbons such as decane?

   [1 mark]

   • ATo remove sulfur impurities from the hydrocarbon before it is used as a fuel
   • BTo break down larger, less useful saturated hydrocarbons into smaller, more useful molecules, including unsaturated ones, since crude oil naturally contains more long-chain molecules than are in demand
   • CTo convert hydrocarbons directly into carbon dioxide and water for safe disposal
   • DTo increase the boiling point of the hydrocarbon fractions produced by distillation

   (c)

   Write a balanced symbol equation for the cracking of decane (C10H22) to produce octane (C8H18) and ethene (C2H4), and identify which of the two products is described as unsaturated.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An atmospheric scientist compares the Moon, which has no significant atmosphere and experiences huge temperature swings from about 120 degrees Celsius in sunlight to about -130 degrees Celsius in darkness, with Earth, whose average surface temperature stays much more stable throughout day and night because of gases present in its atmosphere.

   (a)

   Which gases in Earth's atmosphere are mainly responsible for keeping its surface temperature more stable than the Moon's, by absorbing and re-releasing heat radiated from the surface?

   [1 mark]

   • ANitrogen and oxygen, the two most abundant gases in the atmosphere
   • BArgon and the other noble gases
   • CCarbon dioxide, methane and water vapour
   • DOzone alone, with no meaningful contribution from any other gas

   (b)

   Which statement correctly describes how these gases keep Earth's surface warmer and more stable than it would otherwise be?

   [1 mark]

   • AThese gases reflect sunlight away from Earth before it reaches the surface, keeping the surface cool
   • BThese gases physically trap air molecules near the surface, stopping heat from moving at all
   • CThese gases react chemically with surface rocks, releasing heat as a product of the reaction
   • DThese gases absorb heat energy radiated from the Earth's surface and release this energy in all directions, including back towards the surface, which is known as the greenhouse effect

   (c)

   Explain why the Moon's surface temperature swings by roughly 250 degrees Celsius between day and night, while Earth's does not, in terms of the presence or absence of a suitable atmosphere.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A diesel generator on a construction site is checked by an engineer, who finds that when its air intake filter becomes clogged with dust, the engine produces a smoky black exhaust and the generator's power output drops, compared with when the filter is clean.

   (a)

   Write a balanced symbol equation for the complete combustion of a hydrocarbon fuel such as diesel, represented simply as C12H26, and explain what is meant by the term 'complete combustion'.

   [3 marks]

   (b)

   Explain why the clogged air filter causes incomplete combustion in the generator's engine, name the two extra products that can form when a hydrocarbon fuel burns with an insufficient supply of oxygen, and explain why one of these is particularly dangerous for people working near the generator.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A shipping company is comparing burning heavy fuel oil, which naturally contains sulfur impurities, with burning natural gas (mostly methane, with very little sulfur), to power its cargo ships, and is considering the longer-term effect of its choice of fuel on the atmosphere and the climate.

   (a)

   Explain how burning heavy fuel oil containing sulfur impurities can lead to acid rain, including the gas formed and how it affects rainwater, and explain, using the greenhouse effect, how switching to burning natural gas instead could still contribute to climate change even though it contains far fewer sulfur impurities.

   [6 marks]

   (b)

   Evaluate the advantages and disadvantages of the shipping company switching from heavy fuel oil to natural gas, considering acid rain, contribution to climate change, and one other practical factor of your choice.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A fuel depot manager compares two fuels stored in separate tanks: petrol, a thin, watery liquid that ignites very easily even at room temperature, and bitumen, a thick, sticky, almost solid substance that must be heated before it will flow or ignite.

   (a)

   Which statement correctly explains why petrol and bitumen have such different viscosities and ease of ignition, in terms of the size of their hydrocarbon molecules?

   [1 mark]

   • APetrol molecules are large, with strong intermolecular forces, making petrol viscous and hard to ignite; bitumen molecules are small, with weak forces, making bitumen runny and easy to ignite
   • BPetrol and bitumen are made from completely different chemical elements, which explains the difference in their properties
   • CThe viscosity and ease of ignition of a fuel depend only on its colour, not on the size of its molecules
   • DPetrol molecules are small, with weaker intermolecular forces between molecules, giving petrol a low viscosity and making it easy to ignite; bitumen molecules are large, with much stronger intermolecular forces, giving bitumen a high viscosity and making it hard to ignite

   (b)

   Petrol and bitumen are both described as being mostly members of the same homologous series. Which statement best describes what this means?

   [1 mark]

   • AThey must have identical molecular formulae, with exactly the same number of carbon atoms
   • BThey are elements, not compounds, and so belong to the same family in the periodic table
   • CThey are both mostly composed of alkanes, compounds with the same general formula, which differ from neighbouring members by CH2 in molecular formula and show a gradual variation in physical properties such as boiling point
   • DThe term simply means that both fuels are found within crude oil, with no link to their molecular formulae

   (c)

   State the general formula for the alkane homologous series, and use it to predict the molecular formula of the alkane with 20 carbon atoms, close to the size of molecules typically found in bitumen.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   An environmental scientist studies data showing that the number of cattle farmed worldwide has increased greatly over the last 50 years, alongside a rise in the concentration of methane in the atmosphere over the same period, and a gradual rise in average global temperatures.

   (a)

   Cattle produce methane gas as part of their digestion. Which statement correctly describes the possible link between this and climate change?

   [1 mark]

   • AMethane produced by cattle has no effect on the atmosphere at all, since it is a natural process
   • BIncreased cattle farming could be contributing to rising atmospheric methane, which is a greenhouse gas, potentially contributing to global warming/climate change
   • CMethane produced by cattle immediately breaks down into nitrogen and oxygen, gases already present in the atmosphere
   • DMethane produced by cattle only affects local air quality near the farm and has no link to global climate

   (b)

   Which of the following statements about interpreting this data is correct?

   [1 mark]

   • AA correlation between rising cattle numbers, methane concentration and temperature does not, by itself, prove that livestock farming causes climate change, since other factors (such as fossil fuel use) are also changing over the same period
   • BThe data proves conclusively that livestock farming is the only cause of climate change
   • CSince methane and temperature both rose together, the methane increase must actually be decreasing the temperature
   • DA correlation seen over time always proves that one factor directly causes the other, with no other explanation possible

   (c)

   Suggest one way, other than reducing livestock numbers, that the effects of increased atmospheric methane on climate could be mitigated, and give one reason why any mitigation approach needs to consider its scale and risk.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A geology student examines rock samples believed to be around 2 billion years old, and finds banded iron formations, layers of iron oxide that scientists believe formed when dissolved iron in ancient oceans reacted with oxygen that was just beginning to build up in the water and atmosphere, released by early photosynthetic organisms.

   (a)

   Explain, referring to photosynthesis, how the amount of oxygen in Earth's atmosphere is thought to have gradually increased from an early atmosphere containing little or no oxygen, and describe the chemical test used to confirm the presence of oxygen gas.

   [3 marks]

   (b)

   Explain how the formation of banded iron formations, as described, provides evidence to support the idea that oxygen levels in the ancient oceans and atmosphere increased due to early photosynthetic life, and suggest one limitation of using rock evidence like this to draw conclusions about the ancient atmosphere.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   An island nation that currently generates most of its electricity by burning imported coal and diesel is evaluating switching a large share of its power generation to burning locally produced biogas (mostly methane, made by fermenting agricultural waste), while also monitoring rising sea levels and changing weather patterns linked to climate change.

   (a)

   Explain why burning fossil fuels such as coal and diesel over a long period has contributed to a change in the composition of the Earth's atmosphere compared with its composition a few hundred years ago, and explain, using the greenhouse effect, how this change is linked to the changing weather patterns and rising sea levels the island is monitoring.

   [6 marks]

   (b)

   Evaluate whether switching from burning coal and diesel to burning locally produced biogas (methane) would help the island reduce its impact on climate change, considering where the carbon dioxide released by each fuel originally came from, and considering any other advantages or disadvantages of using biogas instead of imported fossil fuels.

   [6 marks]

   Total for question 8: 12 marks

End of questions