Transcript Slide 1

PowerPoint to accompany
Chapter 20
Environmental
Chemistry
Atmosphere

Temperature varies
greatly with altitude.

However, there is not
a linear relationship
between altitude and
temperature.
Figure 20.1 (a)
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Atmosphere

Although the relationship
between altitude and
pressure is not linear,
pressure does decrease
with an increase in
altitude.
Figure 20.1 (b)
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Composition of the
Atmosphere


Because of the great variation in atmospheric
conditions, the composition of gases in the
atmosphere is not uniform.
Lighter gases tend to rise to the top.
Table 20.1
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Outer Atmosphere

The Sun emits a wide range of wavelengths of
radiation.

Remember that light in the ultraviolet region has
enough energy to break chemical bonds.
Figure 20.2
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Photodissociation

When these bonds break, they do so
homolytically.

Oxygen in the upper atmosphere
absorbs much of this radiation before it
reaches the lower atmosphere.
.. ..
O=O
.. ..
+ h  2
..
O
.. :
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Photoionisation
Table 20.2

Shorter wavelength radiation causes electrons to
be knocked out of molecules in the upper
atmosphere; very little of this radiation reaches
the Earth’s surface.

The presence of these ions makes long-range
radio communication possible.
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Ozone

Ozone absorbs much of the radiation
between 240 and 310 nm.

It is a result of the reaction of molecular
oxygen with the oxygen atoms produced
in the upper atmosphere by
photodissociation.
O + O2  O3
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Ozone Depletion

In 1974, Rowland and Molina discovered that
chlorine from chlorofluorocarbons (CFCs) may
be depleting the supply of ozone in the upper
atmosphere by reacting with it.

CFCs were used for years as aerosol propellants
and refrigerants.

They are not water soluble (so they do not get
washed out of the atmosphere by rain) and are
quite unreactive (so they are not degraded
naturally).
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Chlorofluorocarbons

The C—Cl bond is easily broken though
when the molecule absorbs radiation
with a wavelength between 190 and 225
nm.

The chlorine atoms formed react with
ozone.
Cl + O3  ClO + O2
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Chlorofluorocarbons

In spite of the fact that the use of CFCs
is now banned in over 100 countries,
ozone depletion will continue for some
time because of the tremendously
unreactive nature of CFCs.
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Troposphere

Although the troposphere is made up almost
entirely of nitrogen and oxygen, other gases
present in relatively small amounts still have a
profound effect on the troposphere.
Table 20.3
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Sulfur

Sulfur dioxide is a by-product of the
burning of coal or oil and upon oxidation
to SO3, reacts with moisture in the air to
form sulfuric acid.
SO3(g) + H2O(l)  H2SO4(aq)

It is primarily responsible for acid rain.

High acidity in rainfall causes corrosion
in building materials.
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Sulfur

SO2 can be removed by injecting powdered
limestone which is converted to calcium oxide.

The CaO reacts with SO2 to form a precipitate of
calcium sulfite.
Figure 20.4
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Carbon Monoxide

Carbon monoxide
binds preferentially to
the iron in red blood
cells.

Exposure to significant
amounts of CO can
lower O2 levels to the
point that loss of
consciousness and
death can result.
Figure 20.5
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Carbon Monoxide

Products that can
produce carbon
monoxide must contain
warning labels.

Carbon monoxide is
colourless and
odourless.
Figure 20.6
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Nitrogen Oxides and
Photochemical Smog

What we recognise
as smog, that
brownish gas that
hangs above large
cities, is primarily
nitrogen dioxide, NO2.

It is the result of the
oxidation of nitric
oxide, NO, a
component of car
exhaust.
Figure 20.7
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Nitrogen Oxides and
Photochemical Smog

These nitrogen oxides are just some
components of photochemical smog.

Ozone, carbon monoxide, and hydrocarbons
also contribute to air pollution that causes severe
respiratory problems in many people.

As a result, government emission standards for
automobile exhaust have become continually
more stringent.
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Water Vapour and Carbon
Dioxide

Gases in the atmosphere form an insulating
blanket that causes the Earth’s thermal
consistency.

Two of the most important such gases are
carbon dioxide and water vapour.
Figure 20.8
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Water Vapour and Carbon
Dioxide

This blanketing effect is
known as the “greenhouse
effect.”

Water vapour, with its high
specific heat, is a major
factor in this moderating
effect.

Figure 20.9
But increasing levels of
CO2 in the atmosphere may
be causing an unnatural
increase in atmospheric
temperatures.
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
The World Ocean

The vast ocean contains many important
compounds and minerals.

However, the ocean is only a commercial
source of sodium chloride, bromine, and
magnesium.
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Desalination


“Water, water
everywhere, and not
a drop to drink.”
Seawater has too
high a concentration
of NaCl for human
consumption.
It can be desalinated
through reverse
osmosis.
Figure 20.12
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Reverse Osmosis

Water naturally flows through a semipermeable
membrane from regions of higher water
concentration to regions of lower water
concentration.

If pressure is applied, the water can be forced
through a membrane in the opposite direction,
concentrating the pure water.
Figure 20.12
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Dissolved Oxygen and Water
Quality

Biodegradable is the term used
to refer to organic material that
bacteria are able to oxidise.
However, excessive quantities
of this material leads to oxygen
depletion.

Nitrogen and phosphorus from
fertilisers and detergents are
plant nutrients that contribute
to water pollution by stimulating
excessive growth which leads
to increased dead and
decaying matter and oxygen
depletion, a process called
eutrophication.
Figure 20.14
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Treatment of Water Supplies

Water goes through several filtration
steps.

CaO and Al2(SO4)3 are added to aid in
the removal of very small particles.
Figure 20.15
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Treatment of Water Supplies

The water is aerated to increase the amount of
dissolved oxygen and promote oxidation of
organic impurities.

Ozone or chlorine is used to disinfect the water
before it is sent out to consumers.
Figure 20.15
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
The Challenges of Water
Purification

We have become increasingly aware over the past
decades that modern processes are not always
compatible with maintaining a sustainable environment.

For example, when purifying water through
chlorination, trihalomethanes (suspected carcinogens)
are formed.

HClO(aq) and HBrO(aq) (formed from Cl2(g), H2O(l) and
Br ) will oxidise organics to CHCl3, CHCl2Br, etc.

However, the risks of cancer from these materials in
treated water are very low compared with the risks of
cholera, typhus and gastrointestinal disorders from
untreated water.
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia