C1c - Clean air

Question 1

What is the proportions of the main gases in air(3)

Answer 1

21% oxygen

78% nitrogen

0.035% carbon dioxide

Question 2

What is the theory of the evolution of the atmosphere based on

Answer 2

the composition of gases vented by present day volcanic activity

Question 3

Describe one possible theory for how the present day

atmosphere evolved over millions of years(8)

Answer 3

Volcanoes kept erupting, releasing gases from the earth. This ‘degassing’ released CO2, water vapour and ammonia

Water vapour condensed to form oceans

Carbon dioxide dissolved in the ocean waters

Ammonia reacted with oxygen to form nitrogen gas in the atmosphere

Percentage of nitrogen slowly increased, and since it was unreactive, little nitrogen was removed

Over time, organisms which could photosynthesis evolved
-these organisms converted carbon dioxide and water into oxygen

Percentage of oxygen increased, and the percentage of carbon dioxide decreased until today’s levels were reached

Question 4

Describe the carbon cycle(3)

Answer 4

CO2 is converted into O2 through respiration and forms carbon compounds in plants

These compounds are passed to animals through feeding, and to fossil fuels when the organisms die and is buried

Respiration, combustion of fossil fuels and decay of plants and animals all uses up oxygen and releases carbon dioxide into the atmosphere

Question 5

Evaluate the effects of deforestation on the composition of air(3)

Answer 5

trees cut down in large numbers for human use (building/crops)

trees burnt (combustion) to clear land quickly, releasing CO2

Less trees means less CO2 removed by photosynthesis, so more CO2 in the atmosphere

Question 6

Evaluate the effects of increased population on the composition of air(3)

Answer 6

+respiration, +CO2

+total demand for energy for lighting, heating, cooking, transport, etc
-+combustion of fossil fuels, +CO2

Question 7

Describe the effects of oxides of nitrogen(2)

Answer 7

react with other atmospheric pollutants in sunlight to form a photochemical smog, causes breathing difficulties

reacts with water vapour to produce nitric acid which forms acid rain

Question 8

Describe the effects of sulfur dioxide

Answer 8

reacts with water vapour to form sulfuric acid which forms acid rain

Question 9

Why is it important that atmospheric pollution is controlled? (2)

Answer 9

to reduce damage to human health (atmospheric pollution can cause respiratory problems)

to reduce damage to the environment (acid rain)

Question 10

How are oxides of nitrogen formed

Answer 10

high temperature and pressure inside engine allows nitrogen and oxygen to react and produce oxides of nitrogen

Question 11

Catalytic converter balanced symbol equation

Answer 11

2CO + 2NO → N2 + 2CO2

Question 12

What does a catalytic converter do

Answer 12

converts pollutants (CO, NOx) from car exhaust gases into less dangerous gases (CO2, N2)