Chem Air

Question 1

What is the composition of air?

Answer 1

Nitrogen 78% 
Oxygen 21%
CO2 0.03%
Water vapour 0-5%
Noble gases >1%

Question 2

What does the fractional distillation of liquid air aim to get

Answer 2

Nitrogen and oxygen

Question 3

Steps of fractional distillation of air (2)

Answer 3

1. Air is cooled and compressed into a liquid
2. It is then soersted into its constituents via fractional distillation, lowest bp distills first (N2)
   Boiling points:
   - nitrogen: -196
   - argon: -186
   - oxygen: -183

Question 4

Finding % of oxygen in air (copper)

Answer 4

Known amt of air is passed back and forth over heated copper -> copper II oxide, o2 decrease -> air in syringe decr

Calc:
Vol of o2= initial vol-final vol
%=vol of o2/initial vol

Question 5

Definition of air pollution

Answer 5

Air pollution is the condition in which air contains a high concentration of certain chemicals that may harm living things or damage non-living things

Question 6

3 common air pollutants

Answer 6

1 carbon monoxide CO
2 oxides of nitrogen NOx: NO, NO2
3 sulfur dioxide SO2

Question 7

Sources of carbon monoxide

Answer 7

• incomplete combustion of carboncontaining fuels

- incomplete combustion of petrol in car engines

Question 8

How are oxides of nitrogen produced 2

Answer 8

1. Car engines or factories
   Temp is very high,
   N2 + O2 in air = 2NO
   More oxygen: 2NO + O2 = 2NO2
2. Lightning strikes
   Heat energy released by lightning

Question 9

How do oxides of nitrogen form acid rain

Answer 9

Oxides of N and oxygen and water
4NO2 + O2 + H2O -> 4HNO3
Acid rain

Question 10

How is Sulfur dioxide produced 2

Answer 10

1. Combustion of sulfurcontaining fossil fuels (major source)
   Eg. Coal, crude oil, natural gas -> sulfur as impurities (higher in coal)
   S + O2 =heat= SO2
2. Volcanic eruptions

Question 11

How does sulfur dioxide result in acid rain

Answer 11

Sulfur dioxide and oxygen in air dissolves in rainwater

2SO2 + O2 + 2H2O = 2H2SO4

Question 12

What are some other air pollutants 4

Answer 12

• unburnt hydrocarbons
• methane CH4
• lead Pb
• ozone O3

Question 13

How are unburnt hydrocarbons and lead produced

Answer 13

Unburnt hydrocarbons and lead : car exhaust and chemical plants

Question 14

How is methan producedb

Answer 14

• Bacteria decay of dead plant and dead animal matter, decay of rubbish
• a greenhouse gas -> polar ice caps melt: flooding & drastic weather changes

Question 15

How is ozone produced

Answer 15

NO2 and unburnt hydrocarbons in presence of sunlight

At low altitudes it causes pollution problems, breathing difficulties, and photochemical smog

Question 16

Effect of carbon monoxide on environment

Answer 16

Binds strongly with haemoglobin to form carboxyhaemoglobin, which is very stable and hard to reverse
Cannot transport O2 to the rest of the body -> headaches fatigue breathing difficukties and death

Question 17

Effects of oxides of nitrogen and sulfur dioxide on the environment (acid rain)

Answer 17

Acid rain -> they dissolve in rainwater 
Sulfur dioxide with oxygen and water to sulfuric acid
2SO2 + O2 = 2SO3 
SO3 + H2O =H2SO4 
Nitrogen dioxide to nitric acid 
4NO2 + 2H2O + O2 = 4HNO3

Question 18

Effects of Acid rain

Answer 18

pH of 4 or less

• Metal bridges and stone buildings are corroded
• Reduce pH of natural water bodies, destroy fish and plants
• Leaches impt nutrients from soil, destroys plants and crops. Plant growth stunted
• Irritate eyes, breathing difficulties, inflammation of lungs

Question 19

Impacts of unburnt hydrocarbons

Answer 19

Causes cancer (carcinogenic) 
Reacts with nitrogen oxides to form ozone at low altitudes

Question 20

Impacts of methane on environment

Answer 20

CH4

Greenhouse gas

Question 21

Impacts of ozone on environment

Answer 21

(At low altitudes)
Forms photochemical smog - irritates eyes lungs, breathing difficulties
Damages crops (less O2)

Question 22

Increase of 1 in pH =

Answer 22

10fold in acidity

Question 23

How to reduce effects of acid rain 3

Answer 23

1 Liming - Powdered linestone CaCO3 : neutralise (temp and ex)
2 catalytic converters (vehicles)
3 flue gas desulfurisation (BGD plant)

Question 24

Catalytic converters

Answer 24

Catalysts: platinum and rhodium

Redox reactions
1 carbon monoxide oxidised carbon dioxide
2 oxides of nitrogen reduced nitrogen
3 unburnt hydrocarbons oxidised carbon dioxide and steam

Question 25

Flue gas desulfurisation

Answer 25

1. Remove sulfur from fossil fiels before burning (ex, difficult) 2. Remove sulfur dioxide from waste gases (flue gases) -> desulfurisation (cheaper) Flue gas reacts with an aqueous suspension of moist limestone (calcium carbonate) or moist lime (calcium oxide) = solid calcium sulfite + CO2 gas Calcium sulfite oxidised calcium sulfate (by atmospheric O2)

Question 26

Depletion of Ozone layer O3

Answer 26

Photochemical reaction between O2 and O in atmosphere Advantage: at high altitudes (stratosphere), a shield, filters harmful ultraviolet radiation from sun UV rad -> skin cancer, genetic muration, eye damage, harm marine life

Question 27

What is causing the depletion of ozone in the stratosphere?

Answer 27

Chlorofluorocarbons CFCs 1 carbon 2 fluorine 3 chlorine Are very stable, remain in atmos for very long, slowly diffuse and react with ozone, destroying layer -> more UV

Question 28

Solution for ozone depletion

Answer 28

Ban use of CfCs but stuffs still there for very long

Question 29

Control of air pollution singapore

Answer 29

1 no open fires for disposal of domestic and industrial watse 2 introducing unleaded petrol and phasing out leaded petrol 3 reducing allowed lvl of sulfur in diesel 4 catalytic converters in petrol vehicles

Question 30

Reducing air pollution by motor vehicles 3

Answer 30

1 New materials like lightweight alloys to make car bodies -> lighter = less fuel 2 alternative clean fuels (methanol, hydrongen) -> products of combustion of these are harmless 3 dev of electric vehicles -> reduce exhaust

Question 31

Greenhouse effect

Answer 31

Rate of removal of atmospheric CO2 must be balanced by the rate of return of CO2 to atmosphere Carbon cycle

Question 32

Greenhouse effect- return carbon 3

Answer 32

1 respiration: glucose -> CO2 + water 2 combustion of most fuels -> CO2 + water 3 decay and bacterial decomp -> breakdown of carbon compounds in them

Question 33

Greenhouse effect remove CO2 2

Answer 33

1 photosynthesis: CO2 + water -> glucose + O2 2 ocean uptake: dissolved CO2 used by plants and organisms. Most converted to calcium carbonaye (limsetone) : shells and skeletons -> linsteone

Question 34

Greenhouse gases

Answer 34

Gases that trap radiation -> absorbs radiation, less amt of heat energy into space CH4 and Nitrous oxide -> stronger infrared absorbers than CO2 Water vapour as well

Question 35

Global warming

Answer 35

The incr in temp due to build up of grenhouse gases Human acticities -> burning of fossil fuels, large scale cutting down forests -> rapid build up of gases More return than removal

Question 36

Consequences of global warming 4

Answer 36

1 more unusual weather conditions 2 less crop yield (vegetation->deserts) 3 melting of ice -> ocean lvl rise, flood low lying areas 4 Rapid evap of water: CO2 from water in oceans to atmos