Maintaining Air Quality

Question 1

What is composition of air

Answer 1

78% nitrogen, 21% oxygen, 1% noble gases - mainly argon, 0.03% carbon dioxide

Question 2

How to obtain components of air

Answer 2

Fractional distillation
Air is cooled to obtain water vapour and carbon dioxide. Remaining gases in air are compressed at 150 atm in compressor with huge pumps. Compressed air is allowed to expand rapidly and cools, liquefying the air. Liquid air is distilled in fractionating column, heater is used to boil it. Nitrogen has lowest boiling point and is collected at top, followed by argon, oxygen. Krypton and xenon must be further distilled to separate them

Question 3

Why is air cooled first before fractional distillation

Answer 3

To remove carbon dioxide and water vapour to prevent them from blocking pipes when they solidify during cooling and liquefaction of air

Question 4

Define air pollution

Answer 4

A condition in which air contains a high concentration of chemicals that may harm living things or damage non-living things

Question 5

What are the sources of carbon monoxide

Answer 5

Incomplete combustion of carbon-containing petrol

Question 6

What are harmful effects of carbon monoxide

Answer 6

In presence of carbon monoxide, carbon monoxide binds with haemoglobin in blood more readily compared to oxygen gas. The process is irreversible. Carbon monoxide prevents uptake of oxygen gas by organs. Is highly toxic and can lead to brain damage and death

Question 7

How to treat carbon monoxide

Answer 7

Carbon monoxide pollution can be reduced by fitting motor vehicles with catalytic converters. Catalytic converters oxidises harmful carbon monoxide into harmless carbon dioxide

Question 8

What are sources of sulfur dioxide

Answer 8

Combustion of fossil fuels such as coal and petroleum that contain sulfur as impurities
Volcanic eruptions

Question 9

What are health and environmental effects of sulfur dioxide

Answer 9

Causes eye irritations and breathing difficulties
High levels will lead to inflammation of the lungs
Gives rise to acid rain with pH of about 4 and below
(Sulfur (in source) burns in air to form sulfur dioxide. Sulfur dioxide in air reacts with water to form sulfurous acid H2SO3, which slowly oxidised in air to form sulfuric acid)

Question 10

What are harmful effects of acid rain

Answer 10

Corrodes limestone buildings and marble statues by reacting with carbonates. Corrodes metal structures such as steel bridges. Damages trees and vegetation. Nutrients such as K+ and Ca+ from soil needed by trees for good growth are dissolved by acidic rain and washed away. Destroys aquatic life by killing fish in freshwater lakes and streams.

Question 11

How to treat/prevent sulfur dioxide pollution

Answer 11

Remove sulfur impurities from fossil fuels before they are burnt.
Treat acidic sulfur dioxide gas from waste gases formed before they are released into air. Waste gases known as flue gases are treated with wet mixture of calcium carbonate. Equations:
SO2(g) +CaCO3(s) -> CaSO3(s) + CO2(g)
2CaSO3(s) + O2(g) -> 2CaSO4(s)

Question 12

What are sources of oxides of nitrogen

Answer 12

Internal combustion engines of motor vehicles when nitrogen and oxygen from air react at high temperature. Occurs naturally from lightning activity. During thunderstorms, heat released by lightning causes nitrogen and oxygen in air to react to form nitrogen oxides(first form nitrogen monoxide then nitrogen dioxide)

Question 13

What are harmful effects of nitrogen dioxide

Answer 13

Causes eye irritations and breathing difficulties
High concentration leads to inflammation of lungs
Gives rise to acid rain
Nitrogen dioxide reacts with oxygen and water vapour in air to form nitric acid

Question 14

How to treat or prevent pollution due to oxides of nitrogen

Answer 14

Can be greatly reduced by fitting motor vehicles with catalytic converters. in converter, oxides of nitrogen are reduced to harmless nitrogen gas

Question 15

Combustion of hydrocarbons in engine with excess oxygen

Answer 15

Produces carbon dioxide and water and releases heat

Question 16

Combustion of hydrocarbons in engine with limited oxygen

Answer 16

Carbon particles in the form of soot and carbon monoxide are produced (incomplete combustion)

Question 17

How do cars reduce gas pollution using exhaust system

Answer 17

Catalytic converters are attached to motor vehicle exhaust systems with platinum and rhodium as catalysts

Question 18

What are the reactions that occur in catalytic converter

Answer 18

Carbon monoxide is oxidised to form CO2
Oxides of nitrogen are reduced with carbon monoxide to form N2 and CO2
Unburnt hydrocarbons are oxidised to form CO2 and H2O

Question 19

What are some measures(other than catalytic converter) to reduce air pollution

Answer 19

Use new materials like lightweight alloys to make car bodies so less fuel is needed to power lighter car bodies
Use clean fuels such as hydrogen as the products of combustion are harmless(water in case of H2)
Use electric cars as battery-powered cars reduce exhaust gas emissions

Question 20

Describe global warming

Answer 20

Atmospheric gases trap heat from sun, preventing loss by radiation to outer space, produces warming effect called greenhouse effect. Process is important in keeping earth’s surface at comfortable temperature. Some pollutants are trapping excessive amount of heat in atmosphere, producing slow increase in temperature, increase in temperature is global warming

Question 21

Why are greenhouse gases increasing in volume

Answer 21

Rise in carbon dioxide is due to increase in use and burning of fossil fuels. Rise in methane is believed to be mainly due to bacterial decay of vegetation due to human activities such as destruction of forest and increased farming of rice field

Question 22

What are consequences of global warming

Answer 22

Melting of polar ice caps causes ocean levels to rise and flooding of low-lying land
More extreme weather events. More rainfall in some areas and spread of deserts/droughts in other areas. This will cause decrease in food crops, leading to possible famine.

Question 23

What is the carbon cycle

Answer 23

The mechanism that maintains the amount of carbon dioxide in the atmosphere
(Rate of removal of carbon dioxide = rate of return of carbon dioxide to maintain constant amount of atmospheric carbon dioxide)

Question 24

How is carbon dioxide produced

Answer 24

Respiration. All living things respire and carbohydrates in food are converted to carbon dioxide and water vapour
Combustion of fossil fuels
Bacteria decay - when plants and animals die, bodies are broken down by bacteria

Question 25

How is carbon dioxide remove from atmosphere

Answer 25

Photosynthesis by plants, carbon dioxide and water are converted into glucose and oxygen in presence of sunlight.
Ocean uptake - Large reservoirs or ‘sinks’ for carbon dioxide. Much of dissolved carbon dioxide in oceans is used by plants in photosynthesis or converted to calcium carbonate in form of shells and skeletons of marine organisms.

Question 26

Function of ozone layer

Answer 26

Protects Earth’s surface from excessive harmful ultraviolet rays from the sun

Question 27

What are CFCs

Answer 27

Compounds containing chlorine, fluorine & carbon
Sources: Aerosol propellants and coolants fluids for refrigerators and air-conditioners
Compounds are gases at room conditions and easily made into liquid at small pressure. CFCs are not broken down in ground-level atmosphere and over some years their molecules rise up and diffuse high into atmosphere, where CFC molecules are decomposed by ultraviolet light from sun into reactive chlorine atoms

Question 28

How do CFCs contribute to destruction of ozone layer

Answer 28

Reactive chlorine atom formed will react with ozone molecule to form chlorine monoxide and oxygen gas, destroying ozone molecule. Chlorine monoxide formed can react with reactive oxygen atom(formed when UV breaks down oxygen molecule into single oxygen atoms), regenerating chlorine atom. Cycle will repeated continuously with one chlorine atom destroying thousands of ozone molecules

Question 29

Effects of destroying ozone layer

Answer 29

Enables excessive UV light to reach earth’s surface
Exposure to excessive UV radiation causes skin cancer, eye disease such as cataract and damages food crops