Cook
IB Option E Chemistry
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The effect of human activity on the
environment.
How does it impact:
Air
 Water
 Soil
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3 Key areas of study:
 Atmospheric Pollutants
 Discarded waste in landfills
 Greenhouse gases
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Air is a mixture of the following elements and
percentages:
Gas
% Composition
Nitrogen (N2)
78
Oxygen (O2)
21
Argon (Ar)
1
Water Vapor
1-4
Carbon Dioxide (CO2)
0.04
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Is a substance that has a harmful effect on the
environment and is present in concentrations
greater than it natural levels.
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Effects depend on
 TOXICITY
 Length of time they remain in the enviroment
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Air pollution is classified as Primary and
Secondary
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Primary=emitted directly into the atmosphere
Secondary=produced from primary pollutants
chemical changes.
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CO2
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Produced from the combustion of fossil fuels
CO
Smog
SO2
NO
VOC’s (hydrocarbons)
Now its time to discuss the natural and
anthropogenic sources.
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CO
Toxic to humans because if affects the uptake of oxygen in blood
Its absorbed by the lungs and binds to hemoglobin which prevents
oxygen from binding
 Hb + CO COHb
 Hemoglobin + Carbon monxide= Carboxyhemoglobin
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This prevent oxygen from being transported
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This colorless and odorless compound can cause dizziness and
death at high concentrations
Sources: Anthropogenic =incomplete combustion of fossil
fuels and forest fires
2C + O2  2CO
CO pollution occurs in urban areas with heavy traffic
CO is formed by natural sources during atomspheric oxidation of
methane gas.
 Methane comes from
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Reducing the amount of CO can be done doing
the following:
Lean Burn engines
 Catalytic converter:
 Thermal Exhaust reactor:
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Follows low air/fuel ratios -(14:15 by mass) is
needed for complete combustion
Max power is achieved with mixture richer in
fuel, with lower air/fuel ratio around 12.5 by
mass, but this makes more CO.
Engines misfire with leaner (lower ratios)
Lean burn engines have ratios 18 or higher
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Control Exhaust emissions
Hot gases are mixed with air and passed over a
platinum based catalyst.
Oxidation catalyst are used in lean burn
engines to convert CO to CO2.
3 way catalyst work in conventional engines.
They oxidize CO to CO2 and hydrocarbons to
water and CO2
Review equations on pages 675 HL and 368 SL
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Thermal Exhust Reactors
Take advantage of heat of the exhaust gases and
makes CO react with more air to produce CO2
 Review Figure 16.2
 Know reactions for each CO method of control, both
HL and SL.
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catalyst is a substance that causes or accelerates
a chemical reaction without itself being
affected. Catalysts participate in the reactions,
but are neither reactants nor products of the
reaction they catalyze.
There are two different types of catalyst at
work, a reduction catalyst and an oxidation
catalyst. Both types consist of a ceramic
structure coated with a metal catalyst, usually
platinum, rhodium and/or palladium.
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When an NO or NO2 molecule contacts the
catalyst, the catalyst rips the nitrogen atom out
of the molecule and holds on to it, freeing the
oxygen in the form of O2. The nitrogen atoms
bond with other nitrogen atoms that are also
stuck to the catalyst, forming N2. For example:
2NO => N2 + O2 or 2NO2 => N2 + 2O2
2NO => N2 + O2 or 2NO2 => N2 + 2O2
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The known nitrogen oxides are:
NO (produced from natural decomposition/lightning)
 NO2 (most toxic)
 N2O
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These react with hydrocarbons to form
photochemical smog, nitric acid and contribute to
acid rain.
Motor vehicles are the main source (fig 16.3)
Only under conditions of high temperatures
(15000C in automobile engines), nitrogen and
oxygen in the air react to form NO.
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NO (Most pollutant)
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Produced naturally for decomposition of nitrogen
containing compounds
 Nitrogen Fixing Bacteria and Lightning
 Review reactions of Nitrogen and the nitrogen cycle
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N2O
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Major source is bacteria decomposition
Reacts with hydrocarbons to form photochemical
smog and also forms HNO3 making acid rain
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Lean Burn Engines
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A rich mixture with a high fuel content produces
low Nox, but high CO. Lean burn engines which use
air:fuel ratios : 18:1 can be used to reduce emissions
of both NOx and CO.
Three way catalytic converters
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They oxidize CO to CO2
 2CO + O2  2CO2
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There are 2 types:
 SO2 and SO3
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SO2 is the most dangerous, that can harm
people, plants and materials (buildings)
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Natural sources: Volcanos and rotting veggies
Secondary Pollutant
Review Reaction
Anthropogenic sources: Fossil Fuels (coal)
Review all reactions
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Pre Combustion:
The best way is to remove sulfur before or after combustion.
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Sulfur can be removed by crushing the coal and washing with
water. Sulfide sinks to bottom and separates from clean coal.
 Review Reaction
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Post Combustion
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Alkaline scrubbing Figure 16.4
 A alkaline mixture is sprayed downward unto exhaust gas. The
mixture contains CaO (lime) reacts with SO2 and forms calcium sulfate
which is deposited in landfill.
 Fluidized Combustion
 Coal is mixed with powered limestone on a metal plate as air passes
through the mixture which makes particles float above a plate making a
mixture behave like a fluid. The heat produced from combustion of coal
causes the CaCO3 to break up into CaO and CO2 the SO2 is removed as it
combust with coal.
 See Reaction
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Solid particles of dust, carbon or liquid droplets of mist or
fog.
Have small diameter: 0.001-10micrometers
Very polar and attracted to water and form aerosols.
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Gaseous suspension of very small particles of liquid
Examples:
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Soot (from incomplete combustion of hydrocarbons and coal
burning factories)
Dust
Sulfur from volcanoes
Pollen, bacterial and fungal spores
Arsenic from insecticides
Asbestos
 Material containing silicate crystals which is used to insulate building.
These are released in the air when buildings are demolished.
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Mercury (Fungicides, making of paper and pulp.
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Gravitational Settling by rain and snow
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They can be prevented from entering atmosphere by
Treating industrial emissions using the following
physical methods.
-Flitration
-Centifugal separation
-Settling tanks
-Scrubbing
-Electrostatic precipitation
Review these methods for quiz on weds
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These are organic air pollutants
Methane
Chloroethane
Aromatic hydrocarbons (from incomplete combustion of
coal/wood)
Benzene
VOC’s also released into air from solvents and paints
Hydrocarbons from secondary pollutants
Halogen organic compounds (CFC’S)
Photochemical Smog
Methane is released in large amounts by cows. It is produced by
bacterial anaerobic decomposition of organic material in the water
and soil. Unsaturated hydrocarbons (with double bonds), called
trepenes are given out by plants.
Anthropogenic sources include: Unburned Petroleum products;
Gasoline emitted from car exhaust. Basicaly everything from fossil
fuels
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Using Oxidation Catalytic converters
Using Thermal Exhaust Reactors
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Review all reactions and methods of control
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Two types of Smog
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Photochemical Smog:
 From nitrogen oxides which oxidizes in dry sunshine
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Pea Soup Smog
 Carbon Particulates and SO2
 From reducing