Ch 18 PPT.ppt

(1)

Chemistry of the Environment

Atmosphere

• Temperature varies greatly with altitude. • However, there is

not a linear

relationship between altitude and

(2)

Atmosphere

Although the

relationship between altitude and

pressure is not linear, pressure

does decrease with an increase in

(3)

Composition of the Atmosphere

• Because of the great

variation in atmospheric conditions, the

composition of gases in the atmosphere is not uniform.

(4)

Composition of the Atmosphere

• Near the Earth’s

surface, about 99% of the atmosphere is

composed of nitrogen and oxygen.

(5)

Outer Atmosphere

• The Sun emits a wide range of

wavelengths of radiation.

• Remember that light in the

ultraviolet region

(6)

Radiation

The

atmosphere is the first line of defense against radiation from the Sun.

Processes which absorb radiation

(7)

Photodissociation

• Oxygen in the upper atmosphere

absorbs much of this radiation before it

reaches the lower atmosphere:

(8)

Photoionization

• Shorter wavelength radiation causes electrons to be knocked out of molecules in the upper

(9)

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.

(10)

Ozone Depletion

(11)

Chlorofluorocarbons

• CFCs were used for years as aerosol

propellants and refrigerants.

(12)

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:

(13)

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

(14)

Troposphere

(15)

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.

(16)

Sulfur

• High acidity in rainfall

causes corrosion in building materials.

• Marble and limestone

(17)

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

(18)

Carbon Monoxide

• Products that can produce carbon

monoxide must contain warning labels.

• Carbon monoxide is

(19)

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

(20)

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

(21)

Photochemical Smog

• These nitrogen oxides are just some

components of

photochemical smog. • Ozone, carbon

monoxide, and

hydrocarbons also contribute to air

(22)

Photochemical Smog

As a result,

government emission standards for

automobile exhaust have become

(23)

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

(24)

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.

(25)

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

(26)

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

(27)

Water Purification

• Clean, safe fresh water supplies are of the

utmost importance to society.

(28)

Water Purification

• Water goes through several filtration steps.

• CaO and Al₂(SO₄)₃ are added to aid in the

(29)

Water Purification

• The water is aerated to increase the amount of dissolved oxygen and promote oxidation of organic impurities.

(30)

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.

(31)

Green Chemistry Principles

1. Rather than worry about waste

disposal, it is better to avoid creating

waste in the first place.

2. In addition to generating as little waste

as possible, try to make waste that is

nontoxic.

(32)

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.

(33)

Solvents

(34)

Chlorination of Water

• Chlorination kills waterborne bacteria that cause cholera, typhus, and gastrointestinal disorders like giardia.

• Formation of trihalomethanes: CHCl₃, CHCl₂Br, etc.

• Cl₂  ClO-  THM’s

(35)

Fluoridination of water

• Fluoridination of water: keeps tooth

enamel from demineralizing.

– Currently benefits far outweigh risks from fluorosis.

– Produces lower incidences of cavities esp. in lower income communities which use

(36)

Nuclear Reactors

(37)

Nuclear Reactors

• The reaction is kept in check by the use of control rods.

(38)

Radiation Doses

• Symptoms of acute radiation (within one day): • 0 – 0.25 Sv (0 – 250 mSv): None

• 0.25 – 1 Sv: Some people feel nausea and loss of appetite; bone marrow, lymph nodes, spleen damaged.

• 1 – 3 Sv: Mild to severe nausea, loss of appetite, infection; more severe bone marrow, lymph node, spleen damage; recovery

probable, not assured.

• 3 – 6 Sv: Severe nausea, loss of appetite; hemorrhaging,

infection, diarrhea, peeling of skin, sterility; death if untreated. • 6 – 10 Sv : Above symptoms plus central nervous system

(39)

Radiation Dose

• US measures in rem or mrem. • 100 rem = 1 Sv

• Average dose=0.3 microSv/hr in US • Outside Tokyo: 2-4 microSv/hr

• Chernobyl: 10-30 Sv/hr

• The average American has a 42% risk of developing (not dying from) some kind of cancer in his or her

lifetime. If one of us gets hit with a 300 rem (3 Sv) dose of radiation—a high enough dose that we'd

(40)

Nonmetals

Except for hydrogen, the

(41)

Periodic Trends

(42)

Periodic Trends

(43)

Electron-Sea Model

• Metals can be thought of as cations

suspended in “sea” of valence electrons.

• Attractions hold

(44)

Molecular Orbital Model

These trends can be explained by energy

bands created by large number of molecular orbitals formed as

(45)

Molecular Orbital Model

• As with nonmetals, bond order apexes in center of row, then decreases.

• Thus, attractions (and melting point, etc.) apex in center of transition

(46)

Physical Properties of

Transition Metals

(47)

Electron Configurations and

Oxidation States

• Transition metals often have more than one

common oxidation state.

– Most have +2 state due to loss of s electrons. – Oxidation numbers

greater than 2 are due to the loss of d

(48)

Electron Configurations and

Oxidation States

Many form compounds that have colors.

Mn2+, Fe2+,

Co2+, Ni2+,