Chem Air Flashcards
What is the composition of air?
Nitrogen 78% Oxygen 21% CO2 0.03% Water vapour 0-5% Noble gases >1%
What does the fractional distillation of liquid air aim to get
Nitrogen and oxygen
Steps of fractional distillation of air (2)
- Air is cooled and compressed into a liquid
- It is then soersted into its constituents via fractional distillation, lowest bp distills first (N2)
Boiling points:
- nitrogen: -196
- argon: -186
- oxygen: -183
Finding % of oxygen in air (copper)
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
Definition of air pollution
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
3 common air pollutants
1 carbon monoxide CO
2 oxides of nitrogen NOx: NO, NO2
3 sulfur dioxide SO2
Sources of carbon monoxide
- incomplete combustion of carboncontaining fuels
- incomplete combustion of petrol in car engines
How are oxides of nitrogen produced 2
- Car engines or factories
Temp is very high,
N2 + O2 in air = 2NO
More oxygen: 2NO + O2 = 2NO2 - Lightning strikes
Heat energy released by lightning
How do oxides of nitrogen form acid rain
Oxides of N and oxygen and water
4NO2 + O2 + H2O -> 4HNO3
Acid rain
How is Sulfur dioxide produced 2
- Combustion of sulfurcontaining fossil fuels (major source)
Eg. Coal, crude oil, natural gas -> sulfur as impurities (higher in coal)
S + O2 =heat= SO2 - Volcanic eruptions
How does sulfur dioxide result in acid rain
Sulfur dioxide and oxygen in air dissolves in rainwater
2SO2 + O2 + 2H2O = 2H2SO4
What are some other air pollutants 4
- unburnt hydrocarbons
- methane CH4
- lead Pb
- ozone O3
How are unburnt hydrocarbons and lead produced
Unburnt hydrocarbons and lead : car exhaust and chemical plants
How is methan producedb
- Bacteria decay of dead plant and dead animal matter, decay of rubbish
- a greenhouse gas -> polar ice caps melt: flooding & drastic weather changes
How is ozone produced
NO2 and unburnt hydrocarbons in presence of sunlight
At low altitudes it causes pollution problems, breathing difficulties, and photochemical smog
Effect of carbon monoxide on environment
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
Effects of oxides of nitrogen and sulfur dioxide on the environment (acid rain)
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
Effects of Acid rain
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
Impacts of unburnt hydrocarbons
Causes cancer (carcinogenic) Reacts with nitrogen oxides to form ozone at low altitudes
Impacts of methane on environment
CH4
Greenhouse gas
Impacts of ozone on environment
(At low altitudes)
Forms photochemical smog - irritates eyes lungs, breathing difficulties
Damages crops (less O2)
Increase of 1 in pH =
10fold in acidity
How to reduce effects of acid rain 3
1 Liming - Powdered linestone CaCO3 : neutralise (temp and ex)
2 catalytic converters (vehicles)
3 flue gas desulfurisation (BGD plant)
Catalytic converters
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
Flue gas desulfurisation
- Remove sulfur from fossil fiels before burning (ex, difficult)
- 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)
Depletion of Ozone layer O3
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
What is causing the depletion of ozone in the stratosphere?
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
Solution for ozone depletion
Ban use of CfCs but stuffs still there for very long
Control of air pollution singapore
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
Reducing air pollution by motor vehicles 3
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
Greenhouse effect
Rate of removal of atmospheric CO2 must be balanced by the rate of return of CO2 to atmosphere
Carbon cycle
Greenhouse effect- return carbon 3
1 respiration: glucose -> CO2 + water
2 combustion of most fuels -> CO2 + water
3 decay and bacterial decomp -> breakdown of carbon compounds in them
Greenhouse effect remove CO2 2
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
Greenhouse gases
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
Global warming
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
Consequences of global warming 4
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
