For O level students An overview of air chemistry

1. ENVIRONMENTAL CHEMISTRY
Muhammad Areeb Nafey uddin Siddiqui
Muhammad Aleem Ansari
Haadi Uddin Ahmed
Muhammad Hassaan Fawad

2. PERCENTAGE COMPOSITION OF AIR
Nitrogen-78%
Oxygen-21%
Noble Gases-0.97%
Carbon dioxide0.03%

3. VERIFYING COMPOSITION OF AIR
N2 + O2 + 2Cu
heat
2CuO + N2
•where nitrogen remains unreacted.

4. VERIFYING COMPOSITION OF AIR:
PROCEDURE
100 cm3 of dry air (air is dried by passing over
anhydrous calcium chloride) filled in a graduated
gas syringe
 This air is passed back-and-forth over heated
copper using two syringes, attached on each side
of a hard glass (silica) tube (containing copper)
 On culmination of the experiment, 79 cm3 of dry gas
remains, indicating that 21 cm3 has been used by
copper
 On analysis, the remaining gas is found to be
mainly nitrogen and pink copper metal turns to
black copper (II) oxide


5. LIQUEFACTION OF AIR
Air is mainly comprised to two diatomic
gases, namely nitrogen, N2, and oxygen O2
 By principle, the liquefaction point of air should lie
between those of pure N2 (77K) and pure O2
(90.6K)
 The liquefaction process begins at 81.6K (9K below
the liquefaction point of O2) and completes at 79K
(2K above the liquefaction point of N2), at one
atmospheric pressure
 Industrially, however, 200 atm. is used, so
aforementioned conditions do not necessarily
apply


6. LIQUEFACTION OF AIR

7. LIQUEFACTION OF AIR—PROCESS

8. FRACTIONAL DISTILLATION OF LIQUID AIR
Pale blue liquid air passed
in a fractionating column
heat
Nitrogen starts to boil off
first, at 77K
87K
Argon boils off, at 87K
then
Oxygen boils off, at 90K

9. BOILING POINTS OF COMPONENTS OF AIR
Gas
Boiling Point/K
Xenon
165
Krypton
121
Oxygen
90
Argon
87
Nitrogen
77
Neon
27
Helium
4

10. CARBON CYCLE—DIAGRAMMATIC

11. CARBON CYCLE
Earth’s crust contains carbon compounds
(carbonates, fuels)
 Atmosphere contains carbon in form of carbon
dioxide, mainly released by respiration:
C6H12O6 + 6O2
6CO2 + 6H2O (ΔH = -ve)
 Also released when fuels combust:
C + O2
CO2
 CO2 used by plants to manufacture sugars, in
photosynthesis:
6CO2 + 6H2O
C6H12O6 + 6O2 (ΔH = +ve)
 Decomposition and fossilization return carbon
compounds of living things to soil


12. PRIMARY POLLUTANTS OF AIR
Carbon monoxide
 Methane
 Nitrogen oxides
 Ozone
 Sulfur dioxide
 Unburnt hydrocarbons


13. CARBON MONOXIDE
Naturally produced by photochemical reactions in
the troposphere (5×1012 kg/year), during
breakdown of haemoglobin and in fires
 Also produced due to incomplete combustion of
hydrocarbons
 Greenhouse gas
 Toxic gas, which is the main source of air poisoning
in most countries


headache, nausea, vomiting, dizziness, fatigue
 disorientation, visual disturbance, syncope and seizures

14. METHANE
Produced naturally in rice paddies, decomposition
of biological matter, digestion, coalmines, sea beds
(methane hydrates)
 Main constituent of natural gas
 If CH4 > O2 in blood, displacement can occur (but
rarely), leading to slight emotional, psychological
distress, and fatigue
 Non-carcinogenic and generally not harmful to
health
 Contributes in ozone depletion
 Displaces air, i.e., acts as an asphyxiant:
CH4 + 2O2
CO2 + 2H2O
2CH4 + 3O2
2CO + 4H2O
CH4 + O2
C + 2H2O


15. NITROGEN OXIDES
Collectively known as NOx
 Naturally produced during lightning bolts:

Also produced during combustion of fuels in
automobiles (especially high-speed vehicles) and in
electric power plants
 Leads to increased smog, acid rain and water
quality deterioration
 Significant as an irritant of mucus membranes


16. OZONE
Found naturally in stratosphere & troposphere
 Formed by photochemical reactions between
volatile organic compounds and nitrogen oxides
 Associated with increased mortality, especially in
warm season
 Affect plant mechanisms
 Affects health by:


decrements in lung function (like aggravating astma)
 chest-related problems (coughing, tightness, burning)
 decreasing phagocytic activity of alveolar macrophages

17. SULFUR DIOXIDE
73% of SO2 is released through fossil fuel
combustion
 20% of SO2 is released through other industrial
processes (like smelting of ores)
 Volcanic eruptions lead to increased emissions
 Leads to respiratory problems, like asthma
 Reacts with water vapour to form sulphurous acid:
SO2 (g) + H2O (g)
H2SO3 (l)
This causes acid rain, that result in decomposition
of important stonework & poisoning


18. UNBURNT HYDROCARBONS
Formed by low-temperature combustion of fossil
fuels, and from fuel ‘avoiding’ the flame zones in
combustion engines
 Evaporation of petroleum also leads increased
emissions
 Hydrocarbons like benzene are carcinogenic and
prevent normal cell metamorphosis
 React with UV light and combine with other
pollutants, especially NOx to form photochemical
smog


19. GREENHOUSE EFFECT

20. EFFECTS OF GREENHOUSE GASES
CH4 and CO2 are the main greenhouse gases.
 They maintain warmth on the earth that makes life
possible on the plant.
 Excess release of these gases causes them to be
trapped in the atmosphere, thus they help the
atmosphere retain more heat.
 This leads to a phenomena called ‘global
warming’, consequently leading to climate change.
 Will lead to melting of ice caps and widespread
flooding.
 Desertification and loss of biodiversity may occur.


21. THE OZONE LAYER
30,000 metres above the mean altitude of the earth;
lies in the stratosphere
 Very warm, as absorbs UV light
 Stops clouds & water vapour from escaping
 Ozone depletion occurs due to CFCs (very stable):
Cl + O3
ClO + O2
ClO + O
Cl + O2

O 3+ O 2
2O2 (overall)
 This is an autocatalysed reaction (chlorine)
 Ozone hole aver Antarctica
 Increased UV rays reach earth—skin cancers

22. REMEDIES FOR AIR POLLUTION
Flue gas desulphurisation stops SO2 emissions:
SO2 + CaCO3 → CaSO3 + CO2
 Use of catalytic converters to render CO and NOx
harmless:
2NO + 2CO → 2CO2 + N2
2NO2 + 4CO → 4CO2 + N2
 Using low-temperature combustion engines with
catalytic converters reduces NOx and unburnt
hydrocarbons
 Alternatives to CFCs be introduced
 Strict implementation of Montreal and Kyoto
Protocols be ensured


23. BIBLIOGRAPHY
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Chemistry—A Course for O-Level by Christopher N.
Prescott
http://hyperphysics.phyastr.gsu.edu/hbase/thermo/liqair.html
GCSE Biology by D.G. Mackean
http://en.wikipedia.org/wiki/Carbon_monoxide
http://www.ccohs.ca/oshanswers/chemicals/chem_profil
es/methane.html
http://en.wikipedia.org/wiki/Methane
http://chemwiki.ucdavis.edu/Physical_Chemistry/Acids_
and_Bases/Case_Studies/Acid_Rain/Sources_of_Nitrog
en_Oxides
http://www.epa.gov/iaq/no2.html
http://www.a2gov.org/government/publicservices/system
s_planning/Environment/soe07/cleanair/Pages/nox.aspx
http://www.epa.gov/apti/ozonehealth/population.html
http://www.epa.gov/region07/air/quality/o3health.htm

24. BIBLIOGRAPHY
http://www.epa.gov/airquality/sulfurdioxide/
 http://www.epa.gov/airquality/sulfurdioxide/health.ht
ml
 http://prezi.com/sp-kbyuw0v4v/methane-andunburnt-hydrocarbons-consequences-andresolutions/
 http://en.wikipedia.org/wiki/Unburned_hydrocarbon
 http://papers.sae.org/2009-01-2729/
 http://www.edfenergy.com/energyfuture/images/sch
ematic/greenhouse-effect.jpg
 Environmental Management—A Core Text for O
Level and IGCSE by John Pallister
 http://www.xtremepapers.com/revision/gcse/chemis
try/air_and_water.php
