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GCSE · Chemistry

C9 Chemistry of the Atmosphere

AQA 8461/8462/8463 · Calculator allowed · about 85 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

The composition of the Earth's atmosphere has changed enormously since the planet formed about 4.6 billion years ago.

(a)Which of these is closest to the percentage of nitrogen gas in the Earth's atmosphere today?(1)

A) 21%
B) 78%
C) 95%
D) 0.04%

(b)Which of these is closest to the percentage of oxygen gas in the Earth's atmosphere today?(1)

A) 78%
B) 21%
C) 60%
D) 4%

(c)Which process released most of the gases that made up the Earth's very early atmosphere, about 4.6 billion years ago?(1)

A) Photosynthesis by algae
B) Volcanic activity
C) Human industry
D) Evaporation from oceans

(Total for Question 1 is 3 marks)

For roughly the first billion years of Earth's history, the atmosphere was very different from today's.

(a)Describe the composition of the Earth's atmosphere during its first billion years.(2)

(b)Give two reasons why scientists cannot be completely certain about the exact composition of the Earth's early atmosphere.(2)

(Total for Question 2 is 4 marks)

Over hundreds of millions of years, much of the carbon dioxide in the early atmosphere was removed and locked away.

(a)Explain how the formation of the oceans helped to reduce the amount of carbon dioxide in the early atmosphere.(3)

(b)Describe how carbon dissolved in the oceans became locked away in sedimentary rocks and fossil fuels over millions of years.(3)

(Total for Question 3 is 6 marks)

The table gives estimated percentages of carbon dioxide and oxygen in the Earth's atmosphere at different times in its history.

Time (billion years ago): 4.6	3.5	2.5	1.0	present day (0)
Carbon dioxide (%): 95	80	40	5	0.04
Oxygen (%): 0	0	5	15	21

(The remainder of the atmosphere was made up mainly of nitrogen and other gases.)

(a)Calculate the percentage decrease in atmospheric carbon dioxide concentration between 3.5 billion years ago and 1.0 billion years ago.(2)

(b)Suggest why the concentration of oxygen in the atmosphere began to increase noticeably after about 2.5 billion years ago.(2)

(c)Write a word equation for photosynthesis, the process responsible for this increase in oxygen.(2)

(Total for Question 4 is 6 marks)

Certain gases in the atmosphere are described as 'greenhouse gases' because of the role they play in keeping the Earth warm enough to support life.

(a)Name three gases that contribute to the greenhouse effect.(3)

(b)Explain, in terms of energy transfer, how greenhouse gases help to maintain temperatures on Earth that are suitable for life.(4)

(Total for Question 5 is 7 marks)

Scientists have recorded the concentration of carbon dioxide in the atmosphere continuously since 1950, alongside global average surface temperature.

(a)Describe the trend shown by a graph of atmospheric carbon dioxide concentration plotted against time from 1950 to the present day.(2)

(b)A rise in atmospheric carbon dioxide concentration correlates with a rise in global average temperature over the same period. Evaluate why this correlation alone does not prove that carbon dioxide causes the temperature rise.(3)

(Total for Question 6 is 5 marks)

Human activities that release greenhouse gases contribute to a person's or organisation's 'carbon footprint'.

(a)Define the term 'carbon footprint'.(1)

(b)A family's car releases 0.24 kg of carbon dioxide for every kilometre travelled. Calculate the total mass of carbon dioxide released for a return car journey of 45 km.(3)

(Total for Question 7 is 4 marks)

Governments, organisations and individuals can all take action to reduce carbon dioxide emissions.

(a)Give three ways in which an individual could reduce their personal carbon footprint.(3)

(b)Describe the process of carbon capture and storage (CCS) and explain how it helps to reduce the amount of carbon dioxide entering the atmosphere.(3)

(Total for Question 8 is 6 marks)

Required practical style question. A student investigates the products formed when ethanol (C2H5OH) is burned completely. A spirit burner containing ethanol is lit under a boiling tube, and a cold, dry glass funnel is held just above the flame. The funnel is connected by a delivery tube to a second boiling tube containing 5 cm3 of limewater, so that combustion gases pass through it.

Figure (to be drawn): Simple labelled set-up (no image asset, described in the stem): spirit burner with ethanol beneath a boiling tube; a cold, dry glass funnel held over the flame; delivery tube leading to a second boiling tube containing 5 cm3 limewater.

(a)Name the test used to detect carbon dioxide gas and describe the observation if carbon dioxide is present.(2)

(b)A colourless liquid collects on the cold funnel. Describe a chemical test the student could use to show that this liquid contains water.(2)

(c)Complete the balanced symbol equation for the complete combustion of ethanol: C2H5OH + 3O2 -> ___ + ___(2)

(d)The student's 2.3 g sample of ethanol should theoretically produce 2.7 g of water on complete combustion. The student actually collected 1.8 g of water. Calculate the percentage yield of water.(3)

(e)Suggest two reasons, other than experimental error, why the percentage yield of water was less than 100%.(2)

(f)Evaluate this method, suggesting one improvement that would increase the reliability of the mass of water collected.(2)

(g)Explain why the glass funnel must be cold and dry before the experiment begins.(2)

(Total for Question 9 is 15 marks)

Ice cores, tree rings and historical temperature records all provide evidence about how the Earth's climate has changed over time. Evaluate the evidence that human activities are the main cause of the recent increase in global average temperature. In your answer, you should refer to: historical atmospheric data, the difference between correlation and causation, and the limitations of computer climate models.

(Total for Question 10 is 6 marks)

Burning fossil fuels releases several pollutants in addition to carbon dioxide.

(a)Explain why carbon monoxide, produced by incomplete combustion, is toxic to humans.(2)

(b)Fossil fuels often contain sulfur impurities. Explain how burning these fuels leads to acid rain. Include a balanced symbol equation for the formation of sulfur dioxide from sulfur.(4)

(c)State two problems caused by acid rain.(2)

(Total for Question 11 is 8 marks)

Nitrogen oxides are also released when fuels are burned in vehicle engines.

(a)Explain why nitrogen oxides form inside a car engine but do not form when the same fuel burns in the open air.(2)

(b)Give the balanced symbol equation for the formation of nitrogen monoxide from nitrogen and oxygen.(1)

(c)State one environmental or health problem, other than acid rain, caused by nitrogen oxide pollution.(1)

(Total for Question 12 is 4 marks)

Solid particles, called particulates, are also released when fuels are burned, particularly when combustion is incomplete.

(a)Define the term 'particulates' as used to describe air pollution from combustion.(1)

(b)Explain how particulates in the atmosphere can lead to an effect known as global dimming.(3)

(Total for Question 13 is 4 marks)

Biofuels, made from plant material, are sometimes described as 'carbon neutral'.

(a)Explain why biofuels are sometimes described as carbon neutral.(3)

(b)Give one limitation of describing biofuels as fully 'carbon neutral'.(2)

(Total for Question 14 is 5 marks)

Scientists use computer models to predict how the Earth's climate will change in the future.

(a)State two natural factors, other than human greenhouse gas emissions, that can affect global average temperature.(2)

(b)Higher tier only. Explain why predictions made by computer climate models carry some uncertainty.(3)

(Total for Question 15 is 5 marks)

Higher tier only. Methane burns in oxygen according to the equation: CH4 + 2O2 -> CO2 + 2H2O. Calculate the mass of carbon dioxide produced when 8 kg of methane is completely combusted. (Relative formula masses: CH4 = 16, CO2 = 44)

(Total for Question 16 is 4 marks)

Mark scheme · C9 Chemistry of the Atmosphere

Question 1

(a) B1 B) 78%
(a) Answer: B) 78%
(b) B1 B) 21%
(b) Answer: B) 21%
(c) B1 B) Volcanic activity
(c) Answer: B) Volcanic activity

Question 2

(a) B1 mostly carbon dioxide (oe)
(a) B1 little or no oxygen present, with some water vapour and nitrogen (oe, any one of these gases named)
(a) Answer: The early atmosphere was mostly carbon dioxide, with little or no oxygen, and some water vapour and nitrogen.
(b) B1 the events happened billions of years ago, so there were no direct measurements or observers at the time (oe)
(b) B1 evidence has to be worked out indirectly, e.g. from volcanic gases or from rock/mineral evidence, which is limited and open to interpretation (oe)
(b) Answer: Any two from: the atmosphere existed so long ago that no direct measurements exist; evidence must be inferred indirectly (e.g. from volcanic gases or ancient rocks), which is incomplete and open to interpretation.

Question 3

(a) B1 water vapour in the atmosphere cooled and condensed to form the oceans (oe)
(a) B1 carbon dioxide gas dissolved into the ocean water (oe)
(a) B1 this reduced the concentration/proportion of carbon dioxide in the atmosphere
(a) Answer: Water vapour condensed to form the oceans, and carbon dioxide from the atmosphere dissolved into the ocean water, reducing the amount of carbon dioxide in the atmosphere.
(b) B1 marine organisms used dissolved carbon dioxide (and calcium) to form carbonate shells and skeletons (oe)
(b) B1 when these organisms died, their remains/shells sank and accumulated on the sea floor
(b) B1 over millions of years, these deposits were compressed to form sedimentary rock such as limestone, or, where oxygen was absent, were transformed into fossil fuels (oe)
(b) Answer: Sea organisms used dissolved carbon dioxide to build carbonate shells and skeletons; when they died, these sank and built up on the seabed, and over millions of years were compressed into sedimentary rock (e.g. limestone) or, without oxygen, into fossil fuels.

Question 4

(a) M1 (80 - 5) / 80 x 100 seen, or equivalent method
(a) A1 93.75% (accept awrt 94%) cao
(a) Answer: 93.75% (approximately 94%)
(b) B1 photosynthesising organisms, such as algae (and later plants), evolved (oe)
(b) B1 these organisms released oxygen as a product of photosynthesis, which built up in the atmosphere (oe)
(b) Answer: Photosynthesising organisms such as algae evolved and released oxygen as a waste product of photosynthesis, which gradually built up in the atmosphere.
(c) B1 carbon dioxide + water on the reactants side (oe)
(c) B1 glucose + oxygen on the products side (oe)
(c) Answer: carbon dioxide + water -> glucose + oxygen

Question 5

(a) B1 carbon dioxide
(a) B1 methane
(a) B1 water vapour (accept nitrous oxide or CFCs)
(a) Answer: Carbon dioxide, methane and water vapour (nitrous oxide and CFCs also accepted).
(b) B1 short-wavelength radiation from the Sun passes through the atmosphere and reaches/warms the Earth's surface (oe)
(b) B1 the warmed surface re-radiates energy as longer-wavelength (infrared) radiation (oe)
(b) B1 greenhouse gases absorb this infrared radiation, rather than letting it all escape directly into space (oe)
(b) B1 the absorbed energy is re-radiated in all directions, including back towards the Earth's surface, warming the lower atmosphere (oe)
(b) Answer: Short-wavelength solar radiation passes through the atmosphere and warms the Earth's surface. The surface re-radiates this as longer-wavelength infrared radiation, which greenhouse gases absorb instead of it escaping to space. The gases re-radiate this energy in all directions, including back to the surface, keeping the lower atmosphere warm.

Question 6

(a) B1 carbon dioxide concentration has risen/increased throughout the period (oe)
(a) B1 the rate of increase has itself become greater in more recent decades (oe, accept 'increasing at an increasing rate')
(a) Answer: The graph shows a continuous rise in carbon dioxide concentration from 1950 to the present day, with the rate of increase becoming steeper in more recent decades.
(b) B1 a correlation only shows that two variables change together/at the same time (oe)
(b) B1 it does not show which variable, if either, is causing the change in the other, or whether both are caused by a third factor (oe)
(b) B1 scientists need additional evidence, e.g. testing the physical mechanism by which carbon dioxide absorbs infrared radiation, or ruling out other explanations, before concluding causation (oe)
(b) Answer: A correlation only shows that two variables change together, not that one causes the other; the change could be coincidental or caused by a third factor. Scientists need further evidence, such as demonstrating the physical mechanism of CO2 absorbing infrared radiation, before concluding causation.

Question 7

(a) B1 the total amount of carbon dioxide (and other greenhouse gases) released into the atmosphere, e.g. over the life cycle of a product, service or activity (oe)
(a) Answer: The total amount of greenhouse gases (mainly carbon dioxide) released into the atmosphere as a result of an individual's, organisation's or product's activities.
(b) M1 45 x 2 = 90 km (recognising a return journey is double the one-way distance)
(b) M1 90 x 0.24 (dependent on first mark)
(b) A1 21.6 kg (cao, allow awrt 21.6 kg)
(b) Answer: 21.6 kg

Question 8

(a) B1 any one from: using public transport, walking or cycling instead of car travel
(a) B1 any one from: using renewable energy sources at home, or improving home insulation to reduce energy use
(a) B1 any one from: eating less meat/reducing food miles, flying less, or recycling more (any three distinct valid points from the list, max 3)
(a) Answer: Any three from: using public transport/walking/cycling instead of driving; using renewable energy or improving home insulation; eating less meat or reducing food miles; flying less; recycling more.
(b) B1 carbon dioxide produced by power stations/industrial processes is captured/separated from other waste gases (oe)
(b) B1 the captured carbon dioxide is transported, e.g. by pipeline (oe)
(b) B1 it is injected into and stored in porous rock or depleted oil/gas reservoirs (often deep underground or under the seabed), preventing it entering the atmosphere (oe)
(b) Answer: Carbon dioxide from power stations or industrial processes is captured before it is released, transported (e.g. by pipeline), and injected into porous rock or depleted oil/gas reservoirs for long-term storage, preventing it entering the atmosphere.

Question 9

(a) B1 bubble the gas through limewater
(a) B1 the limewater turns cloudy/milky
(a) Answer: Bubble the gas through limewater; if carbon dioxide is present, the limewater turns cloudy (milky).
(b) B1 add the liquid to white anhydrous copper sulfate (oe, cobalt chloride paper also accepted)
(b) B1 the anhydrous copper sulfate turns blue (oe, cobalt chloride paper turns from blue to pink) if water is present
(b) Answer: Add the liquid to white anhydrous copper sulfate; if water is present it turns blue (or use cobalt chloride paper, which turns from blue to pink).
(c) M1 products identified as carbon dioxide and water
(c) A1 2CO2 + 3H2O, fully balanced cao
(c) Answer: C2H5OH + 3O2 -> 2CO2 + 3H2O
(d) M1 percentage yield = actual yield / theoretical yield x 100 identified
(d) M1 1.8 / 2.7 x 100 (dependent on first mark)
(d) A1 66.7% (accept awrt 66.7% or 67%) cao
(d) Answer: 66.7%
(e) B1 any one from: incomplete combustion occurred, producing soot/carbon monoxide instead of full conversion to CO2 and water (oe)
(e) B1 any one from: some water escaped as vapour without condensing on the funnel, or heat/gas was lost to the surroundings (oe, max 2 for two distinct valid reasons)
(e) Answer: Any two from: incomplete combustion occurred (producing some soot/carbon monoxide rather than full conversion); some water vapour escaped without condensing on the funnel; heat or gas was lost to the surroundings.
(f) B1 a valid improvement identified, e.g. repeat the experiment (with the same mass of ethanol) and calculate a mean mass of water collected, or use a larger/more effective condensing surface (oe)
(f) B1 linked justification, e.g. this would reduce the effect of any one anomalous result, or would condense a greater proportion of the water vapour produced (oe)
(f) Answer: Repeat the experiment and calculate a mean mass of water collected, to reduce the effect of any anomalous result; or use a larger/colder condensing surface to condense a greater proportion of the water vapour produced.
(g) B1 cold, so that water vapour produced by combustion condenses on the funnel and can be collected as a liquid (oe)
(g) B1 dry, so that no water is already present on the funnel that would give a false/misleading result (oe)
(g) Answer: The funnel must be cold so that water vapour from combustion condenses on it and can be collected as liquid water; it must be dry so there is no water already present that would give a false result.

Question 10

Level 1 (1-2): Simple, isolated statements are made about historical data and/or human causes of climate change, with little or no linkage between them. No reasoned conclusion is reached.
Level 2 (3-4): Some relevant evidence linking human activity to rising temperatures is described, with some awareness that correlation does not always mean causation and/or that climate models have limitations. Linkage between points is only partly developed.
Level 3 (5-6): A detailed, logically structured evaluation is given. Historical data, the correlation/causation distinction and the limitations of climate models are all used to reach a well-reasoned conclusion about the strength of the evidence for human-caused warming.
Indicative content:
- Ice core and other historical records show that atmospheric carbon dioxide concentration has risen sharply since the industrial revolution, alongside a rise in global average temperature.
- This is a strong correlation, but correlation alone does not prove causation; other factors, such as natural variation in solar output or volcanic activity, could in principle also explain some temperature change.
- However, isotopic analysis of the extra carbon in the atmosphere shows it has a chemical signature matching fossil fuels, supporting the conclusion that human combustion of fossil fuels is the source of the additional carbon dioxide.
- The rate of recent warming is much faster than warming seen in past natural climate cycles (e.g. the end of past ice ages), which is difficult to explain by natural causes alone.
- Computer climate models that exclude human greenhouse gas emissions fail to reproduce the observed rise in temperature, whereas models that include human emissions match the observed data much more closely, supporting a causal link.
- Climate models do have limitations: they rely on simplifying assumptions, use incomplete historical data, and cannot perfectly account for every natural variable (e.g. volcanic eruptions or ocean current changes), so their predictions carry some uncertainty.
- Despite this uncertainty, the overall weight of evidence (historical data, isotopic evidence and model comparisons) leads the great majority of climate scientists to conclude that human activity is the main cause of recent warming.

Question 11

(a) B1 carbon monoxide binds to haemoglobin in red blood cells, in place of oxygen (oe)
(a) B1 this reduces the amount of oxygen that can be carried around the body/to cells, which can cause suffocation or death (oe)
(a) Answer: Carbon monoxide binds to haemoglobin in red blood cells instead of oxygen, reducing the amount of oxygen transported around the body, which can lead to suffocation or death.
(b) B1 S + O2 -> SO2 (correctly balanced equation)
(b) B1 sulfur impurities in the fuel react with oxygen during combustion, releasing sulfur dioxide gas (oe)
(b) B1 sulfur dioxide dissolves in atmospheric water droplets/rainwater (oe)
(b) B1 reacting to form (dilute) sulfurous/sulfuric acid, which falls to the ground as acid rain (oe)
(b) Answer: S + O2 -> SO2. Sulfur impurities in the fuel burn to form sulfur dioxide gas, which dissolves in rainwater/atmospheric water droplets and reacts to form dilute sulfurous or sulfuric acid, which falls as acid rain.
(c) B1 any one from: damages/kills trees and plants; acidifies lakes and rivers, harming or killing aquatic life; corrodes/erodes buildings and statues, especially those made of limestone or marble (any two distinct points, max 2)
(c) B1 second distinct valid point from the list above
(c) Answer: Any two from: damages trees and plants; acidifies lakes and rivers, harming aquatic life; corrodes buildings and statues, particularly limestone or marble structures.

Question 12

(a) B1 inside the cylinder, combustion produces a much higher temperature and pressure than in the open air (oe)
(a) B1 this provides enough energy for nitrogen and oxygen from the air to react together, which does not happen at normal (lower) temperatures found in open-air burning (oe)
(a) Answer: The high temperature and pressure inside the engine cylinder provide enough energy for nitrogen and oxygen from the air to react together, which does not happen at the lower temperatures reached when fuel burns in the open air.
(b) B1 N2 + O2 -> 2NO cao
(b) Answer: N2 + O2 -> 2NO
(c) B1 contributes to photochemical smog (oe), or causes/worsens respiratory problems (oe)
(c) Answer: Contributes to photochemical smog, or causes/worsens respiratory problems in humans.

Question 13

(a) B1 tiny solid particles (e.g. soot/unburned carbon) released into the air, mainly from incomplete combustion (oe)
(a) Answer: Tiny solid particles, such as soot, released into the air, mainly as a result of incomplete combustion.
(b) B1 particulates in the atmosphere reflect some sunlight back into space, reducing the amount reaching the Earth's surface (oe)
(b) B1 particulates can also act as nuclei around which water droplets form, increasing cloud cover, which further blocks sunlight (oe)
(b) B1 the overall effect is a reduction in the amount of sunlight reaching the surface, known as global dimming (oe)
(b) Answer: Particulates reflect sunlight back into space and can encourage extra cloud formation by acting as nuclei for water droplets; both effects reduce the amount of sunlight reaching the Earth's surface, an effect known as global dimming.

Question 14

(a) B1 as the biofuel crop grows, it absorbs carbon dioxide from the atmosphere through photosynthesis (oe)
(a) B1 this absorbed carbon dioxide roughly balances/is approximately equal to the carbon dioxide released when the biofuel is later burned (oe)
(a) B1 so there is little or no net increase in atmospheric carbon dioxide over the fuel's life cycle (oe)
(a) Answer: Biofuel crops absorb carbon dioxide from the atmosphere as they grow, which roughly balances the carbon dioxide released when the fuel is burned, so there is little or no net increase in atmospheric carbon dioxide overall.
(b) B1 growing, harvesting, processing and transporting the biofuel crop itself releases carbon dioxide, e.g. from fossil-fuelled machinery, fertiliser production or transport (oe)
(b) B1 these additional emissions are not accounted for by the simple 'carbon neutral' balance, so biofuels are not truly/fully carbon neutral in practice (oe, alternative valid point: land-use change, e.g. clearing forest to grow biofuel crops, releases stored carbon)
(b) Answer: Growing, processing and transporting biofuel crops itself releases carbon dioxide (e.g. from machinery, fertiliser production or transport, or from land-use change such as deforestation), which is not accounted for by the simple carbon-neutral balance, so biofuels are not truly carbon neutral in practice.

Question 15

(a) B1 volcanic eruptions, which release ash/aerosols that can reflect sunlight and cool the climate (oe)
(a) B1 variation in the Sun's output/solar radiation reaching the Earth (oe)
(a) Answer: Volcanic eruptions (releasing ash and aerosols that reflect sunlight) and variation in the Sun's output/solar radiation reaching Earth.
(b) B1 models rely on assumptions and simplifications of an extremely complex climate system (oe)
(b) B1 models are based on historical data that may be incomplete or limited, especially over very long timescales (oe)
(b) B1 models cannot fully predict feedback effects or future human behaviour/emissions choices, which affect how accurate long-term predictions can be (oe, any three distinct valid points, max 3)
(b) Answer: Climate models rely on simplifying assumptions about a very complex system, are based on historical data that may be incomplete, and cannot fully predict feedback effects or future human choices about emissions, so their long-term predictions carry uncertainty.

Question 16

M1 convert 8 kg to 8000 g and find moles of methane: 8000 / 16 = 500 mol
M1 use the 1:1 mole ratio of CH4 to CO2 in the equation to give 500 mol CO2 (dependent on first mark; ft their moles of methane if the ratio is applied correctly)
M1 mass of CO2 = 500 x 44 = 22000 g (dependent on second mark)
A1 22 kg (cao, allow awrt 22 kg; ft their moles of CO2 if method otherwise correct)
Answer: 22 kg

Chemistry of the Atmosphere - Worksheets, Questions and Revision