Oxford Revise AQA GCSE Chemistry | Chapter C18 answers

Question

Answers

Extra information

Mark

AO / Specification reference

01.1

points plotted correctly

line of best fit drawn

1

1

AO2

AO3

4.9.3.1

01.2

average concentration of carbon dioxide in the atmosphere increases with time

1

AO3

01.3

burning more fossil fuels

releases more carbon dioxide into the atmosphere/carbon dioxide that was trapped in the fossils

deforestation

less trees to remove carbon dioxide from the atmosphere

accept other sensible answers that specifically relate to carbon dioxide in the atmosphere

1

1

1

1

AO1

4.9.2.2

02.1

oxides of nitrogen

1

AO1

4.9.3.1

02.2

incomplete combustion

‘incomplete’ must be present to gain mark

1

4.9.3.1

02.3

C₄H₁₀ + 4½O₂ → 4CO + 5H₂O

or

2C₄H₁₀ + 9O₂ → 8CO + 10H₂O

1

AO2

4.9.3.1

02.4

oxides of nitrogen – breathing problems

carbon monoxide – poisoning of humans

particulates – global dimming

1

1

1

AO1

4.9.3.2

02.5

sulfur dioxide

1

AO1

4.9.3.2

03.1

advantages:

• reduction in combustion of fossil fuels so less carbon dioxide released
• provide new jobs
• alternatives can be sustainable

disadvantages:

• some alternatives to fossil fuels still produce carbon dioxide
• alternatives to fossil fuels not always as reliable
• alternatives can be expensive
• jobs from fossil fuel industry could be lost
• not all governments may be able to afford to invest in alternatives to fossil fuels

accept other sensible answers

one mark per correct answer up to a maximum of four marks

to receive full marks, at least one advantage and one disadvantage must be provided

4

AO3

03.2

advantages:

• reduces deforestation
• some farming/cattle farming can produce greenhouse gases

disadvantages:

• prevents population from farming/producing enough food/making money
• unfair to South American countries

accept other sensible answers

one mark per correct answer up to a maximum of three marks

to receive full marks, at least one advantage and one disadvantage must be provided

3

AO3

03.3

advantages:

• reduction in greenhouses gases released
• reduction in pollutants released

disadvantages:

• some forms of alternative transports (e.g. trains and buses) still release greenhouse gases
• relies on good public transport/government investment in transport
• lots of people rely on cars/not always possible to travel by public transport

accept other sensible answers

one mark per correct answer up to a maximum of four marks

to receive full marks, at least one advantage and one disadvantage must be provided

4

AO3

04.1

Level 3: The descriptions of the comparisons are detailed and accurate.

5-6

AO1

AO2

4.9.1.1

Level 2: The descriptions of the comparisons are correct, although lacks detail.

3-4

Level 1: The descriptions of the comparisons lacks clarity and coherence.

1-2

No relevant content.

0

Indicative content

• Mars’ atmosphere is mainly CO₂
• but the percentage of CO₂ in Earth’s atmosphere is only about 0.04%
• both atmospheres include nitrogen and argon
• but the percentage of nitrogen in Earth’s atmosphere is much greater than that on Mars (around 80% on Earth, about 2% on Mars)
• percentage of argon in both atmospheres is similar, at around 1%
• both atmospheres include oxygen
• but the percentage of oxygen in Earth’s atmosphere is much greater than that on Mars (around 20% on Earth, less than 1% on Mars)

04.2

1

AO2

04.3

cannot observe directly

accept other suitable reasons

1

1

AO3

4.9.1.2

04.4

greenhouse gases (carbon dioxide, methane, and water vapour) present in atmosphere

percentage of the atmosphere made of carbon dioxide is greater on Mars than on Earth

but Mars’ atmosphere is less dense therefore less radiation from the Sun is absorbed by the atmosphere

reduced greenhouse effect

1

1

1

1

AO3

4.9.2.1

04.5

sublimation

1

AO1

4.2.2.1

05.1

2 O atoms with 1 ring each

one O atom has 6 crosses, the other 6 dots

O atoms share 1 pair of crosses and 1 pair of dots

1

AO1

4.2.2.1

05.2

little oxygen in atmosphere

algae and plants evolved

carried out photosynthesis

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

as algae and plants increased, so did the percentage of oxygen in the atmosphere

levelled response

1

1

1

2

1

AO1

4.9.1.3

05.3

trees carry out photosynthesis

carbon dioxide converted to other products

therefore, reduce volume of greenhouse gases in atmosphere

1

1

1

AO1

4.9.1.4

05.4

acid rain damages plant life/trees

therefore, less plants carrying out photosynthesis and removing carbon dioxide from the atmosphere

1

1

AO3

4.9.2.2

06.1

greenhouse gases in the atmosphere maintain temperatures in Earth high enough to support life/absorb and re-emit infrared radiation

1

AO1

4.9.2.1

06.2

methane/water vapour

1

AO1

4.9.2.2

06.3

burning fossil fuels

deforestation

accept other correct answers

1

1

AO1

4.9.2.2

06.4

rising sea levels

more extreme weather events

species extinctions

accept any three correct effects

1

1

1

AO1

4.9.2.3

07.1

120 × 100 = 12 000 g

12 000 g = 12 kg

1

1

AO2

4.9.2.4

07.2

1

AO1

4.9.2.4

07.3

mass of carbon dioxide = 1050 × 120 = 126 000 g or 126 kg

22 people for a smaller mass of CO₂ per person

1

1

1

AO2

4.9.2.4

07.4

cars are more convenient

accept any sensible answer

1

AO3

4.9.2.4

08.1

0.68 °C

1

AO2

08.2

2015, 2016, 2017, 2018

all four required for the mark

1

AO2

08.3

2001

1

AO2

08.4

global annual mean surface temperature increases with time

1

AO3

08.5

increase in greenhouse gases in the atmosphere due to:

• burning fossil fuels leading to the release in carbon dioxide
• cattle farming releases methane
• deforestation so less carbon dioxide removed from the atmosphere
• decomposition of landfill releases methane

one mark for each correct answer, up to a maximum of two marks

2

AO1

4.9.2.2

08.6

student is correct for the years 2016 to 2018

but since 2000, the overall trend is up

the time period from 2016 to 2018 is not long enough to draw a firm conclusion

1

1

1

AO3

4.9.2.2

09.1

to allow people to reduce their carbon footprints

accept other suitable answers

1

AO3

4.9.2.4

09.2

• most vegetarian foods produce less carbon dioxide emissions than meat
• so vegetarian diet likely to have lower carbon dioxide emissions
• however, if a person swapped chicken for cheese, they could increase carbon dioxide emissions

1

1

1

AO3

4.9.2.4

09.3

8 kg for beef + 3 kg for cheese

= 11 kg

1

1

AO2

4.9.2.4

09.4

cattle farming produces methane

1

AO3

4.9.2.4

10.1

no direct observations (because so long ago)

1

AO1

4.9.1.2

10.2

Level 3: The descriptions of the explanations are detailed and accurate. The reasons given are clear and coherent.

5-6

AO1

4.9.1.2

4.9.1.3

4.9.1.4

Level 2: The descriptions of the explanations are correct, although lacks detail. Reasons are given for some, although these may not be clearly explained.

3-4

Level 1: The descriptions of the explanations and reasons lacks clarity and coherence.

1-2

No relevant content.

0

Indicative content

carbon dioxide:

• percentage of carbon dioxide has decreased
• water vapour from volcanoes condensed to form oceans
• carbon dioxide dissolved in the oceans
• removed during formation of fossil fuels
• removed during formation of sedimentary rocks
• removed during photosynthesis

oxygen:

• percentage of oxygen increased
• algae and plants first produced oxygen by photosynthesis
• about 2.7 million years ago
• as more algae and plants grew, the percentage of oxygen in the atmosphere increased

10.3

methane

carbon dioxide

accept other correct answers

1

1

AO1

4.9.2.2

10.4

global climate change

accept an effect of global climate change (e.g., rising sea levels, more extreme weather, changes in rainfall, changes to ecosystems, polar ice caps melting)

1

AO1

4.9.2.2

11.1

shorter wave radiation emitted from the Sun passes through the atmosphere

emitted by the Earth as longer wave radiation

greenhouse gases in the atmosphere trap some of the longer wave radiation

trapping the energy and warming the Earth

1

1

1

1

AO1

4.9.2.1

11.2

produces sulfur dioxides that cause acid rain

acid rain damages plants

plants carry out photosynthesis, which removes carbon dioxide from the atmosphere

1

1

1

AO2

4.9.3.1

11.3

human activity leads to increase in carbon dioxide and methane in the atmosphere

as greenhouse gases, they increase the average temperature of the Earth

therefore, this will in turn cause more water vapour to be held by the atmosphere

as water vapour is also a greenhouse gas, this will further enhance the greenhouse effect

leading to a further increase in the average temperature of the Earth/global climate change

1

1

1

1

1

AO2

4.9.2.2

12.1

dissolve a sample of each compound in water

mix with sodium hydroxide solution

aluminium and calcium compounds will form white precipitate.

add more sodium hydroxide and aluminium precipitate will dissolve

iron(II) compound will form green precipitate

1

1

1

1

1

AO1

4.8.3.2

12.2

dissolve sample of iron compound in water

add barium chloride and dilute hydrochloric acid

sulfates will form white precipitate/barium sulfate

1

1

1

AO1

4.8.3.5

12.3

FeSO₄ + 2NaOH → Fe(OH)₂ + Na₂SO₄

2

AO2

4.8.3.2

12.4

A: calcium iodide

C: aluminium chloride

1

1

AO2

4.8.3.4

13.1

energy/enthalpy

ignore units

1

AO1

4.6.1.4

13.2

A

1

AO2

4.5.1.2

13.3

endothermic

because energy of products greater/higher than energy of reactants

1

1

AO2

4.5.1.2

13.4

thermal decomposition/citric acid and sodium hydrogencarbonate/photosynthesis

1

AO1

4.5.1.2

14.1

2 C atoms are drawn with 2 shells, first shell has 2 dots 2 shell has 6 dots and 2 crosses

4 H atoms are drawn with 1 shell which has 1 dot and 1 cross

each H atom shares 1 dot and 1 cross with a C atom, with each C atom sharing with 2 H atoms

C atoms share 4 dots

3

AO2

4.2.1.4

4.7.2.1

14.2

two pairs of electrons are shared in a C=C bond compared to one pair of shared electrons in C−C

1

AO2

4.7.2.1

14.3

in reactions with ethene, the C=C double bond becomes a C-C single bond

C=C double bound is weaker/requires less energy to break than C-C single bond (642 – 348 = 294)

1

1

AO3

4.7.2.2