Aqueous Equilibria

1. Chemistry
of the
Environment
Chapter 18
Chemistry of the
Environment
Chemistry, The Central Science, 10th edition
Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten
John D. Bookstaver
St. Charles Community College
St. Peters, MO
© 2006, Prentice Hall, Inc.

2. Chemistry
of the
Environment
Atmosphere
• Temperature varies
greatly with altitude.
• However, there is
not a linear
relationship between
altitude and
temperature.

3. Chemistry
of the
Environment
Atmosphere
Although the
relationship between
altitude and
pressure is not
linear, pressure
does decrease with
an increase in
altitude.

4. Chemistry
of the
Environment
Radiation
The atmosphere is
the first line of
defense against
radiation from the
Sun.

5. Chemistry
of the
Environment
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.

6. Chemistry
of the
Environment
Composition of the Atmosphere
• Near the Earth’s
surface, about 99% of
the atmosphere is
composed of nitrogen
and oxygen.
• Oxygen has a much
lower bond enthalpy
than nitrogen, and is
therefore more reactive.

7. Chemistry
of the
Environment
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.

8. Chemistry
of the
Environment
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:
O2 + hν → 2 O

9. Chemistry
of the
Environment
Photoionization
• 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.

10. Chemistry
of the
Environment
Ozone
• Ozone absorbs much of the radiation
between 240 and 310 nm.
• It forms from reaction of molecular oxygen
with the oxygen atoms produced in the upper
atmosphere by photodissociation.
O + O2 → O3

11. Chemistry
of the
Environment
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.

12. Chemistry
of the
Environment
Chlorofluorocarbons
• 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).

13. Chemistry
of the
Environment
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

14. Chemistry
of the
Environment
Chlorofluorocarbons
In spite of the fact that the use of CFCs
in now banned in over 100 countries,
ozone depletion will continue for some
time because of the tremendously
unreactive nature of CFCs.

15. Chemistry
of the
Environment
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.

16. Chemistry
of the
Environment
Sulfur
• Sulfur dioxide is a by-product
of the burning of coal or oil.
• It reacts with moisture in the
air to form sulfuric acid.
• It is primarily responsible for
acid rain.

17. Chemistry
of the
Environment
Sulfur
• High acidity in rainfall
causes corrosion in building
materials.
• Marble and limestone
(calcium carbonate) react
with the acid; structures
made from them erode.

18. Chemistry
of the
Environment
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.

19. Chemistry
of the
Environment
Carbon Monoxide
• Carbon monoxide
binds preferentially to
the iron in red blood
cells.
• Exposure to significant
amount of CO can
lower O2 levels to the
point that loss of
consciousness and
death can result.

20. Chemistry
of the
Environment
Carbon Monoxide
• Products that can
produce carbon
monoxide must contain
warning labels.
• Carbon monoxide is
colorless and odorless,
so detectors are a good
idea.

21. Chemistry
of the
Environment
Nitrogen Oxides
• What we recognize as
smog, that brownish
gas that hangs above
large cities like Los
Angeles, is primarily
nitrogen dioxide, NO2.
• It forms from the
oxidation of nitric oxide,
NO, a component of
car exhaust.

22. Chemistry
of the
Environment
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.

23. Chemistry
of the
Environment
Photochemical Smog
As a result,
government emission
standards for
automobile exhaust
have become
continually more
stringent.

24. Chemistry
of the
Environment
Water Vapor 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
vapor.

25. Chemistry
of the
Environment
Water Vapor and Carbon Dioxide
• This blanketing effect is
known as the “greenhouse
effect.”
• Water vapor, with its high
specific heat, is a major
factor in this moderating
effect.
• But increasing levels of
CO2 in the atmosphere
may be causing an
unnatural increase in
atmospheric
temperatures.

26. Chemistry
of the
Environment
Oceans
• The vast ocean
contains many
important compounds
and minerals.
• However, the ocean is
only a commercial
source of sodium
chloride, bromine, and
magnesium.

27. Chemistry
of the
Environment
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.

28. Chemistry
of the
Environment
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.

29. Chemistry
of the
Environment
Water Purification
• Clean, safe fresh water
supplies are of the
utmost importance to
society.
• There are many steps
involved in purifying
water for a municipal
water supply.

30. Chemistry
of the
Environment
Water Purification
• Water goes through
several filtration steps.
• CaO and Al2(SO4)3 are
added to aid in the
removal of very small
particles.

31. Chemistry
of the
Environment
Water Purification
• 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.

32. Chemistry
of the
Environment
Green Chemistry
• We have become increasingly aware
over the past 30 to 40 years that modern
processes are not always compatible with
maintaining a sustainable environment.
• Promoting chemical processes that are
environmentally friendly is part of the
good stewardship chemists should
exhibit.

33. Chemistry
of the
Environment
Green Chemistry Principles
1. Rather than worry about waste
disposal, it is better to avoid creating
waste in the first place.
2. Try to generate as little waste as
possible, and try to make waste that is
nontoxic.
3. Be energy conscious in designing
syntheses.

34. Chemistry
of the
Environment
Green Chemistry Principles
4. Catalysts that allow the use of safe
chemicals should be employed when
possible.
5. Try to use renewable feedstocks as
raw materials.
6. Try to reduce the amount of solvent
used, and try to use environmentally
friendly solvents.

35. Chemistry
of the
Environment
Solvents
Solvents such as supercritical water and CO2
are great “green” alternatives.

36. Chemistry
of the
Environment
Reagents
• Phosgene, COCl2, is
commonly used as a
starting material for
plastic polymers.
• Phosgene is a highly
toxic substance, and
the by-products of
many of its reactions
are undesirable.

37. Chemistry
of the
Environment
Reagents
A superior
alternative might be
dimethyl carbonate.