21 — maintaining air quality

Question 1

Volume composition of gases in dry air

Answer 1

Nitrogen: appx 78%
O2: appx 21%
CO2: appx 0.04%
Noble gases (mainly argon): appx 0.96%

Question 2

Common pollutants

Answer 2

CO
nitrogen oxides (NO, NO2)
Sulfur dioxide
Methane
Unburnt hydrocarbons
Ozone

Question 3

Carbon monoxide property, sources and harmful effects (PSH)

Answer 3

P: a toxic, colourless and odourless gas

S: incomplete combustion of carbon-based fuels such as petrol in car engines

Harmful effects:
CO is toxic and binds irreversibly with haemoglobin in RBCs and lowers the ability to transport O2 to the rest of the body, may result in death

Question 4

Nitrogen oxides property, sources and harmful effects (PSH)

Answer 4

P:
NO -> colourless, odourless
NO2 -> red-brown, pungent smell

S:
1. Lightning activity
2. Internal combustion engines of vehicles (O2 and N2 reacts at high tempts)

H:
1. SO2 and nitrogen oxides react w oxygen in air to form acidic compounds, which dissolve in rain water, forming acid rain

Question 5

Sulfur dioxide property, sources and harmful effects (PSH)

Answer 5

P: colourless gas w pungent smell

S:
1. Volcanic eruptions
2. Combustion of fossil fuels

H:
1. Causes respiratory difficulties
2. SO2 and nitrogen oxides react w oxygen in air to form acidic compounds, which dissolve in rain water, forming acid rain

Question 6

Methane property, sources and harmful effects (PSH)

Answer 6

P: highly flammable colourless and odourless gas

S:
1. Anaerobic bacteria decay of organic substances
2. Waste gases from cattle

H:
1. CH4 is a major greenhouse gas that leads to global warming

Question 7

Unburnt hydrocarbons property, sources and harmful effects (PSH)

Answer 7

P: Colourless and odourless gas; may be pungent due to fuel additives

S: vehicle combustion engines

H:
1. It causes eye and respiratory tract irritation
2. It reacts w nitrogen oxides in the presence of sunlight to form photochemical smog which appears as brown haze. Formation of smog also produces O2, SO2 and NO2

Question 8

Ozone property, sources and harmful effects (PSH)

Answer 8

P: pale blue gas w pungent smell

S:
1. Lightning activity
2. Reactions betw O2 and sunlight in the upper atmosphere
3. Reactions betw Unburnt hydrocarbons and nitrogen oxides in the presence of sunlight in the lower atmosphere

H:
1. Causes eye and respiratory tract irritation, leading to respiratory difficulties
2. When inhaled, causes chest pains and headaches
3. Ozone slows down photosynthesis in plants, which can dmg crops.

Question 9

Solutions to problems arising from air pollutants

Answer 9

1. Catalytic converters
2. Flue gas desulfurisation

Question 10

Redox reactions in catalytic converters to remove combustion pollutants

Answer 10

Catalytic converters contain a coating of catalysts made up of platinum, palladium and rhodium that speed up the conversion of harmful substances in the vehicle exhaust into less harmful substances. The catalysts are arranged in a honeycomb structure that animist the surface area for gases to interact with

Gases that leave the engine contains: CO2, CO, N2, NO2, NO, O2, CxHy (Unburnt hydrocarbons) and H2O (g)

Preferred pollution control as original pollutants from engine r more harmful than CO2

Question 11

Redox reactions in catalytic converters

Answer 11

Removal:
1. CO is oxidised to CO2
2CO (g) + O2 (g) ->. 2CO2 (g)

2. Nitrogen oxides r reduced to nitrogen
   2NO (g) + 2CO (g) -> N2(g) + CO2(g)
   2NO2(g). -> N2 (g) + 2O2(g)
3. Unburnt hydrocarbons r oxidised to CO2 and H2O
   2C8H18 (g) + 25O2 (g) -> 16CO2(g) + 18H2O (g)

Question 12

Flue gas desulfirisation

Answer 12

Fossil fuels have significant Sulfur content. Combustion of fuels produce SO2, known as flue gas.

*- can remove a significant proportion of SO2 from the flue gas before it is released into the atmosphere. In wet scrubbing, calcium carbonate slurry (limestone + water) can remove SO2 from flue gas, reducing the effect of acid rain.

*- Challenge:
1.Set-up requires large amount of space and can be quite costly to run.
2. Using low sulfur fuels will go a long way in reducing amt of Sulfur dioxide in atmosphere -> Solution: Removing excess sulfur from fossil fuels by treating it w H2 gas, producing hydrogen sulfate (H2S) as by-product

CaCO3 is basic and reacts w SO2 which is acidic

Question 13

Redox reactions in flue gas desulfurisation

Answer 13

1. Calcium carbonate reacts w SO2 to form calcium sulfate and CO2
   CaCO3 (s) + SO2 (g) -> CaSO3 (s) + CO2 (g)
2. Calcium sulfite is further oxidised to form calcium sulfate
   2CaCO3 (s_ + O2 (g) -> 2CaSO4 (s)
3. Calcium sulfate can then be hydrated to form hydrated calcium sulfate aka gypsum
   CaSO4 (s) + 2H2O (l) -> 2CaSO4.2H2O (s)

Question 14

Acid rain

Answer 14

pH around 4.0; Formed when acidic pollutants eg sulfur dioxide and nitrogen dioxide dissolve in rainwater

1. Sulfur dioxide dissolves in water to form sulfurous acid
   SO2 (g) + H2O (l) -> H2SO3 (aq)
   In presence of oxygen in air, sulfurous acid is slowly oxidised to nitric acid
2. In presence of O2 and H2O, nitrogen dioxide is converted to nitric acid
   4NO2 (g) + 2H2O (l) + O2 (g) -> 4HNO3 (aq)

Question 15

Effects of acid rain

Answer 15

1. Leaches essential nutrients like Mg and Ca from the soil and causes trees/plants to wither and die
2. Lowers pH of soil/water bodies, which may be too acidic for many plant species/aquatic life to survive, hence killing them
3. Corrodes buildings and structures made from limestone, marble and metals

Question 16

Benefits of ozone

Answer 16

Pollutant at ground level, beneficial at stratosphere.

1. Absorb UV radiation, thus reducing amt of UV radiation that reaches the Earth’s surface
   - Ozone has a pale blue colour + pungent smell.
   - O2 molecules interact w UV radiation from sun to form ozone molecules. They break up to reform oxygen when they absorb UV radiation.

Question 17

How chlorofluorocarbons affect ozone layer

Answer 17

Chlorofluorocarbons (CFCs) are found in aerosol propellants, refrigerants and certain kinds of plastics. They contain fluorine, carbon and chlorine atoms. They r v stable and remain in atmosphere for long periods.

When CFCs rise up the stratosphere, they interact w UV radiation to produce chlorine atoms that react w ozone, destroying the ozone layer. If ozone depletion continues, more harmful UV radiation will reach the earth causing skin cancer.

Question 18

Carbon cycle

Answer 18

Carbon cycle describes a set of processes that regulates the amount of carbon dioxide in the atmosphere. The carbon cycle describes how carbon-containing compounds r converted from 1 form to another. It involves land, water, lakes and atmospheres.

Question 19

Main processes that produce CO2 in carbon cycle

Answer 19

1. Respiration
   Energy is released during respiration thus process is exothermic. Respiration converts glucose in food we eat into CO2 and H2O

C6H12O6 + 6O2 -> 6CO2 + 6H2O

2. Combustion
   An exothermic reaction occurs when fossil fuels r burnt in the presence of oxygen to release energy. Carbon dioxide and water vapour r byproducts
3. Decomposition
   Aerobic decomposition (in presence of O2) releases CO2 in the atmosphere

Question 20

Main processes in carbon cycle which removes CO2

Answer 20

1. Photosynthesis
   Plants help to remove CO2 from the atmosphere thru photosynthesis. Energy is absorbed during photosynthesis in the endothermic reaction
   6CO2 + 6H2O -> C6H12O6 + 6O2
2. Ocean uptake
   Oceans and other large bodies of water absorb CO2. Dissolved CO2 is used by marine plants to photosynthesise and convert to carbonic acid and calcium carbonate that makes up the shells of marine organisms. When organisms die, they accumulate on seabed.

Question 21

Greenhouse gases and their major sources

Answer 21

methane is a stronger GHG than CO2

Sources of GHG:
CO2:
1. Combustion of fossil fuels in power plants, industries and vehicles
2. Deforestation

Methane:
1. Waste gas from cattle
2. Leakage from methane reservoirs under the arctic tundra and from oceanic methane ice.

Question 22

Global warming

Answer 22

Global warming is the increase in the average temperature of the Earth’s surface due to the increasing amount of greenhouse gases in the atmosphere.

Question 23

Climate change phenomenas

Answer 23

1. Desertification of fertile land
2. More frequent and severe heat waves
3. Increase in frequency and intensity of extreme weather
4. Ocean warming and acidification
5. Glacial retreat and melting of polar ice caps

Question 24

Desertification of fertile land Effects

Answer 24

1. Change in rainfall pattern results in desertification in areas receiving too little rain, or flooding in areas receiving too much rain
2. Leads to lower crop Imelda and thus the amt of food that can be reproduced globally would decrease

Question 25

More frequent and severe heat waves Effect

Answer 25

1. Some parts of the world become too hot for humans to live in. High tempts can be fatal for frail nd elderly
2. Higher global tempts lead to wildfires which could destroy whole ecosystem

Question 26

Increase in frequency and intensity of extreme weather effect

Answer 26

1. Tropical storms occur more
2. Property is destroyed and lives may be lost
3. Cyclonic storms can permanently decrease the fertility of farmland near the coast due to saltwater deposition

Question 27

Ocean warming and acidification Effect

Answer 27

1. Coral reefs r bleached, marine biodiversity decreases w habitats lost
2. Commercially-impt fish populations depleted
3. Acidified waters dissolve shells of crustaceans

Question 28

Glacial retreat and melting of polar ice caps

Answer 28

1. Glacier-fed river levels would change
2. Sea levels would rise and permanently flood coastal areas
3. Large amt of fresh water disrupt ocean currents which distribute heat around the globe and stabilise global climate. Such disruption would amplify effects of climate change

Question 29

Explain why planting more trees is not a long term solution to the increase in amount of CO2 [2]

Answer 29

Trees take years to grow thus absorption of CO2 thru photosynthesis is much slower than the release of CO2 to the atmosphere from exhaust fumes of motor vehicles.

Question 30

Suggest why helium cannot be recovered if it is released into the atmosphere [1]

Answer 30

Helium has a relatively low density thus it can easily rise up to the atmosphere. Since it is extremely low in concentration when released into the atmosphere, it is impossible to be recovered.

Question 31

Characteristics of SO2

Answer 31

It is an acidic oxide
It is a pollutant which leads to the erosion of buildings
It is released from volcanoes
It is an Oxidising agent which changes purple acidified KMnO4 solution to colourless.

Question 32

Explain why it is important for CO to be collected and burnt [2]

Answer 32

CO is a poisonous gas which must be burned so that non-toxic CO2 can be formed and released.

Question 33

Equation to form nitric acid from NO2

Answer 33

4 NO2 + 2H2O + O2 —> 4HNO3

Question 34

The DEF tank can cause an explosion when too hot. Explain why [1]

Answer 34

When urea reacts with water, 2 gases r produced. At high temperatures, gaseous particles will gain a lot of energy and cause pressure in tank to increase, causing an explosion.

Question 35

Benefits of using xxx to treat exhaust gases

Answer 35

Convert oxides of nitrogen to nitrogen gas and water which r non-polluting

Ammonia which is highly soluble in water and may leech into water bodies causing an increase in the pH of water, is removed.