Water in the atmosphere- Acid rain
Ions in pure water
H2O
autoionization
neutralization
H+ + OH-
][
]][[
2 OH
OHH
K e q
??
?
214
2
10
]][[
][
M
OHH
OHK e qK
w
?
??
?
?
?
pH value of pure water
p O HpHpK
OHHK
OHHK
w
w
w
??
????
?
??
??
]l o g []l o g [l o g
]][[
In pure water,autoionization is the only source of
ions,therefore:
7
10][][ 7
?
?? ???
pH
MOHH
A pH of 7 defines neutrality,pH<7 means acidic and
pH>7 is basic,
What is the pH of natural rain water?
MCOH
x
COH
p
COH
OHK
OHCO
COH
K
COHOHgCO
CO
eq
eq
9.4
32
6
325.1
32
2
22
32
3222
10][
10370
][
10
][
][
]][[
][
)(
2
?
?
?
?
?
?
?
??
pH of natural rain water is
determined by acidic and
basic species that are
naturally present in the
atmosphere,
Equilibrium
constant
CO2 partial pressure
in unit of atm
Unit,M
CO2,370 ppm
What is the pH of natural rain water?
(Continued)
7.5
10][
1010][][
][
][
][
]][[
)10(
7.5
9.44.6
32
2
32
2
32
3
4.6
332
?
?
??
?
?
???
??
???
?
??
???
pH
H
xCOHKH
COH
H
K
COH
H C OH
K
KH C OHCOH
a
a
a
a
Rainwater is naturally acidic because its equilibrium with
carbon dioxide.
][][ 3 ?? ? H C OH
Acid rain
? Rainwater has a pH of 5.7 if CO2 is the only species
that affects its acidity.
? When additional acidic species are present at
appreciable levels as a result of man-made activities,
pH of rain water becomes lower than 5.7.? Acid rain.
? H2SO4 and HNO3 are the major contributors to acid
rain.
pH of acid rain
H2SO4 and HNO3 are the major contributors to acid rain.
Sources for H2SO4 and HNO3 in the air
? Both substances are formed in the air
– Precursor to H2SO4,SO2
– Precursor to HNO3,NO2
? Concentrations of the precursors SO2 and
NO2 are greatly increased by man-made
activities,especially fossil fuel combustion.
Role of NH3 in acid rain
? Ammonia dissolved in rainwater scavenges H+:
– NH3 (aq) + H+ = NH4+
? Ammonia input lowers the acidity in rain.
Ion Rural New York Southwest Minnesota
(meq/l) (meq/l)
H+(pH) 46 (4.34) 0.5 (6.31)
SO42- 45 46
NO3- 25 24
HCO3- 0.1 10
NH4+ 8.3 38
The larger input of NH3 in MN is responsible for the lower
rain acidity than in NY.
Production of NH3
? Animal waste,
? ammonification of humus followed by
emission from soils
? losses of NH3-based fertilizers from soils
? industrial emissions.
Acid Rain,Cross-boundary Pollution
A large portion of SO2 and NO2 produced in one
country is exported to others by prevailing
surface winds,
– Canada-U.S.A,More than half the acid deposition in
heavily populated southern Canada originates from
seven central and upper midwestern states-Ohio,
Indiana,PA,IL,Missouri,WV,and TN,where coal
and oil-burning power and industrial plants are
concentrated,
– Asian-Pacific
Effects of acid rain
? Acidification of surface water (lakes,rivers,etc),and
subsequent damage to aquatic ecosystems.
– kills aquatic plants,fish and microorganisms in lakes and
streams by releasing ions of Al,Pb,Hg and Cd from soils
and sediments.
? Damage to forests and vegetation
– Weakens or kills trees,especially conifers at high
elevations;
– Makes trees more susceptible to diseases,insects,drought,
and fungi and mosses that thrive under acidic conditions;
– Stunts growth of crops such as tomatoes,soybeans,
spinach,carrots,broccoli and cotton
Acid rain has scarred the pine forest at Clingman’s Dove in the
Smoky Mountain
Effects of acid rain (Continued)
? Damage of materials and structures
– building materials,statues,metals,cars,
– CaCO3 + H2SO4--> CaSO4 + CO2 + H2O
– CaSO4 occupies more volume than CaCO3 and is more
soluble than CaCO3.
? Harm to human beings
– irritation to eyes,inflammation of lung tissue,respiratory
illness,etc.
? Degradation of regional visibility
Study questions
1,Why is natural rainwater acidic,with a pH
value of 5.7?
2,What are the major pollutants that can alter
the natural rain water pH?
3,Statues made of lime stone have been
observed to lose their original fine features,
Explain the reason behind this phenomenon.
Ions in pure water
H2O
autoionization
neutralization
H+ + OH-
][
]][[
2 OH
OHH
K e q
??
?
214
2
10
]][[
][
M
OHH
OHK e qK
w
?
??
?
?
?
pH value of pure water
p O HpHpK
OHHK
OHHK
w
w
w
??
????
?
??
??
]l o g []l o g [l o g
]][[
In pure water,autoionization is the only source of
ions,therefore:
7
10][][ 7
?
?? ???
pH
MOHH
A pH of 7 defines neutrality,pH<7 means acidic and
pH>7 is basic,
What is the pH of natural rain water?
MCOH
x
COH
p
COH
OHK
OHCO
COH
K
COHOHgCO
CO
eq
eq
9.4
32
6
325.1
32
2
22
32
3222
10][
10370
][
10
][
][
]][[
][
)(
2
?
?
?
?
?
?
?
??
pH of natural rain water is
determined by acidic and
basic species that are
naturally present in the
atmosphere,
Equilibrium
constant
CO2 partial pressure
in unit of atm
Unit,M
CO2,370 ppm
What is the pH of natural rain water?
(Continued)
7.5
10][
1010][][
][
][
][
]][[
)10(
7.5
9.44.6
32
2
32
2
32
3
4.6
332
?
?
??
?
?
???
??
???
?
??
???
pH
H
xCOHKH
COH
H
K
COH
H C OH
K
KH C OHCOH
a
a
a
a
Rainwater is naturally acidic because its equilibrium with
carbon dioxide.
][][ 3 ?? ? H C OH
Acid rain
? Rainwater has a pH of 5.7 if CO2 is the only species
that affects its acidity.
? When additional acidic species are present at
appreciable levels as a result of man-made activities,
pH of rain water becomes lower than 5.7.? Acid rain.
? H2SO4 and HNO3 are the major contributors to acid
rain.
pH of acid rain
H2SO4 and HNO3 are the major contributors to acid rain.
Sources for H2SO4 and HNO3 in the air
? Both substances are formed in the air
– Precursor to H2SO4,SO2
– Precursor to HNO3,NO2
? Concentrations of the precursors SO2 and
NO2 are greatly increased by man-made
activities,especially fossil fuel combustion.
Role of NH3 in acid rain
? Ammonia dissolved in rainwater scavenges H+:
– NH3 (aq) + H+ = NH4+
? Ammonia input lowers the acidity in rain.
Ion Rural New York Southwest Minnesota
(meq/l) (meq/l)
H+(pH) 46 (4.34) 0.5 (6.31)
SO42- 45 46
NO3- 25 24
HCO3- 0.1 10
NH4+ 8.3 38
The larger input of NH3 in MN is responsible for the lower
rain acidity than in NY.
Production of NH3
? Animal waste,
? ammonification of humus followed by
emission from soils
? losses of NH3-based fertilizers from soils
? industrial emissions.
Acid Rain,Cross-boundary Pollution
A large portion of SO2 and NO2 produced in one
country is exported to others by prevailing
surface winds,
– Canada-U.S.A,More than half the acid deposition in
heavily populated southern Canada originates from
seven central and upper midwestern states-Ohio,
Indiana,PA,IL,Missouri,WV,and TN,where coal
and oil-burning power and industrial plants are
concentrated,
– Asian-Pacific
Effects of acid rain
? Acidification of surface water (lakes,rivers,etc),and
subsequent damage to aquatic ecosystems.
– kills aquatic plants,fish and microorganisms in lakes and
streams by releasing ions of Al,Pb,Hg and Cd from soils
and sediments.
? Damage to forests and vegetation
– Weakens or kills trees,especially conifers at high
elevations;
– Makes trees more susceptible to diseases,insects,drought,
and fungi and mosses that thrive under acidic conditions;
– Stunts growth of crops such as tomatoes,soybeans,
spinach,carrots,broccoli and cotton
Acid rain has scarred the pine forest at Clingman’s Dove in the
Smoky Mountain
Effects of acid rain (Continued)
? Damage of materials and structures
– building materials,statues,metals,cars,
– CaCO3 + H2SO4--> CaSO4 + CO2 + H2O
– CaSO4 occupies more volume than CaCO3 and is more
soluble than CaCO3.
? Harm to human beings
– irritation to eyes,inflammation of lung tissue,respiratory
illness,etc.
? Degradation of regional visibility
Study questions
1,Why is natural rainwater acidic,with a pH
value of 5.7?
2,What are the major pollutants that can alter
the natural rain water pH?
3,Statues made of lime stone have been
observed to lose their original fine features,
Explain the reason behind this phenomenon.
